(en)Methods and compositions are provided to increase the activity/level of an RKD polypeptide or an active variant or fragment thereof in an unreduced ovule plant cell that is outside of the embryo sac. In specific embodiments, such modulation of activity/level of the RKD polypeptide promotes an egg cell-like state in an unreduced ovule plant cell that is outside of the embryo sac. Such methods and compositions can employ an expression construct comprising a RKD polypeptide or active variant or fragment thereof operably linked to an ovule tissue-preferred promoter, in particular an ovule tissue-preferred promoter that is active in at least one non-gametophyte tissue in a plant ovule and is active in an unreduced cell that is outside of the embryo sac.

1.ApplicationNumber: US-201213445447-A
1.PublishNumber: US-2013180010-A1
2.Date Publish: 20130711
3.Inventor: CHAMBERLIN MARK A.
LAWIT SHAI J.

4.Inventor Harmonized: CHAMBERLIN MARK A(US)
LAWIT SHAI J(US)

5.Country: US
6.Claims:
(en)Methods and compositions are provided to increase the activity/level of an RKD polypeptide or an active variant or fragment thereof in an unreduced ovule plant cell that is outside of the embryo sac. In specific embodiments, such modulation of activity/level of the RKD polypeptide promotes an egg cell-like state in an unreduced ovule plant cell that is outside of the embryo sac. Such methods and compositions can employ an expression construct comprising a RKD polypeptide or active variant or fragment thereof operably linked to an ovule tissue-preferred promoter, in particular an ovule tissue-preferred promoter that is active in at least one non-gametophyte tissue in a plant ovule and is active in an unreduced cell that is outside of the embryo sac.

7.Description:
(en)CROSS-REFERENCE
This utility application claims the benefit U.S. Provisional Application No. 61/583,649, filed Jan. 6, 2012, which is incorporated herein by reference.


FIELD OF THE DISCLOSURE
The present disclosure relates to the field of plant molecular biology, more particularly to regulated gene expression in plants from ovule tissue-preferred promoters expressed in unreduced, somatic tissues of the ovule.
BACKGROUND OF THE DISCLOSURE
Apomixis refers to asexual reproduction leading to the production of seeds without fertilization, leading to offspring genetically identical to the mother plant (Koltunow, et al., (1995) Plant Physiol. 108:1345-1352; Ravi, et al., (2008) Nature 451:1121-1124). It is a reproductive process that bypasses female meiosis and syngamy to produce embryos identical to the maternal parent. Apomixis increases the opportunity for developing superior gene combinations and facilitates the rapid incorporation of desirable traits. Apomixis not only provides reproductive assurance, but also avoids a loss of heterozygosity in the offspring because the egg cell maintains the parental genotype. Apomixis therefore avoids the effects of loss of vigor due to inbreeding and may additionally confer some advantages because of the heterosis affects.
At the species level, apomixis occurs in less than 1% of the species. Apomixis occurs in many wild species and in a few agronomically important species such as citrus and mango, but not in any of the major cereal crops (Eckhardt, (2003) The Plant Cell 15:1449-1501). One form of apomixis is adventitious embryony, where embryos are formed directly out of somatic tissues within the ovules outside an embryo sac. Adventitious embryony usually occurs in parallel to normal sexual reproduction. Because it offers the promise of the fixation and indefinite propagation of a desired genotype, there is a great deal of interest in engineering this ability to produce clonal seeds into crops, especially cereals (Spillane, et al., (2001) Nat. Biotechnol. 22:687-691).
A molecular approach to engineer apomixis in commercial plant lines is highly desirable. Regulation of gene transcription plays a substantial role in expression of seed-specific developmental programs. Therefore, the regulation of the molecular switch during early ovule development, at the point of divergence between sexual reproductive pathways and apomictic processes, is a point at which apomictic-like traits can be controlled.
Expression of heterologous egg-specific DNA sequences in a plant host is dependent upon the presence of operably linked regulatory elements that are functional within the plant host at the correct time and the correct place. Choice of the promoter sequence will determine when and where within the organism the heterologous DNA sequence is expressed. Adventitious embryony requires expression of a DNA sequence in particular tissues or organs of a plant that are in a particular growth or developmental phase. Such a DNA sequence may be used to promote or inhibit plant growth processes, thereby affecting the growth rate or architecture of the plant. Often limiting the expression of developmental specific genes to relevant tissues during embryogenesis is required for viable offspring.
Isolation and characterization of somatic ovule-tissue preferred transcriptional regulators, that can serve as regulators of expression of genes in the apomictic pathway early in seed development, are needed for impacting various traits in plants and the development of synthetic adventitious embryony.
BRIEF SUMMARY OF THE DISCLOSURE
Methods and compositions are provided to increase the activity/level of a RKD polypeptide or an active variant or fragment thereof in an unreduced ovule plant cell that is outside of the embryo sac. In specific embodiments, such modulation of activity/level of the RKD polypeptide promotes an egg cell-like state in an unreduced ovule plant cell that is located outside of the embryo sac. Such methods and compositions can employ an expression construct comprising a RKD polypeptide or active variant or fragment thereof operably linked to an ovule tissue-preferred promoter, in particular, an ovule tissue-preferred promoter that is active in at least one non-gametophytic tissue in a plant ovule and is active in an unreduced cell that is outside of the embryo sac.



BRIEF DESCRIPTION OF THE DRAWINGS
This patent or application file contains at least one drawing figure executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
FIG. 1(A-D) demonstrates the expression pattern of a heterologous gene (GUS) operably linked of the Arabidopsis NUC1 promoter of the disclosure, and the modified NUC1 (ALT1) promoter disclosure in ovules. (A) is a reference schematic of of an Arabidopsis ovule with a mature embryo sac, showing the egg (red), 2 synergids (green), central cell (blue) and the 3 antipodals (yellow). Expression at the (B) megagametophyte, (C) egg and (D) globular embryo stages. The expression pattern is visible in micropylar tip of inner integuments, spreads chalazally through the inner integuments surrounding the micropylar half of embryo sac. Expression transitions from the micropylar inner integuments to the chalazal integuments during the globular embryo stage (D) and at the heart-shaped embryo stage expression was observed only in integuments opposite the chalazal end (not shown). FIGS. 1B-D are differential interference contrast (DIC) images of cleared Arabidopsis ovules showing blue GUS-staining.
FIG. 2 demonstrates the expression pattern of a heterologous gene (DS-RED) operably linked to the promoter AT-CYP86C1 (PHP43541) in ovules at (A) the egg stage, (B) torpedo embryo stage and (C) the late globular embryo stage. The expression pattern is visible in micropylar tip of inner integuments (A), spreads chalazally through the endothelium to surround the base of the embryo sac, also spreads into the micropylar end of outer integuments (B) and then continues to spread chalazally through the entire endothelial layer (C). FIGS. 2A-C are DIC images (blue-green tinted) of Arabidopsis ovules overlayed with a DS-RED fluorescence images.
FIGS. 3 and 4 demonstrate the expression pattern of a heterologous gene (DS-RED) operably linked to the promoter AT-CYP86C1 (PHP43541) in ovules at the egg stage. At the mature embryo sac stage (Egg stage) AT-CYP86C1 pro:Ds-Red expression is localized to the inner integuments surrounding and opposite the micropylar end of the embryo sac. FIG. 3 is a stereoscope image of Arabidopsis ovules using mixed fluorescence (DS-RED) and bright-field optics. FIG. 4 is a DIC image (blue-green tinted) of an Arabidopsis ovule overlayed with a DS-RED fluorescence image.
FIG. 5 demonstrates the expression pattern of a heterologous gene (DS-RED) operably linked to the promoter AT-CYP86C1 (PHP43541) in an ovule at the egg/zygote stage. At or following fertilization AT-CYP86C1 pro:Ds-Red expression is still localized to the inner integuments surrounding and opposite the micropylar end of the embryo sac. Expression extends chalazally in the endothelium layer beginning on the abaxial side (left) of the ovule. FIG. 5 is a DIC image (blue-green tinted) of an Arabidopsis ovule overlayed with a DS-RED fluorescence image.
FIGS. 6(A and B) DIC and fluorescence images demonstrate the expression pattern of a heterologous gene (DS-RED) operably linked to the promoter AT-CYP86C1 (PHP43541) in an ovule at the zygote stage. AT-CYP86C1 pro:Ds-Red expression remains strongly localized to the inner integuments surrounding and opposite the micropylar end of the embryo sac (B). Expression extends chalazally in the endothelium layer beginning on the abaxial side of the ovule. Also expression can be seen in the outer integuments opposite the micropylar end of the embryo sac. FIG. 6A is a DIC image of a single Arabidopsis ovule. FIG. 6B is the same DIC image (blue-tinted) and overlayed with a DS-RED fluorescence image.
FIGS. 7 and 8 ( 7 A-C and 8 A-C) demonstrates the expression pattern of a heterologous gene (RED) operably linked to the promoter AT-CYP86C1 (PHP43541) in an ovule at the torpedo stage. AT-CYP86C1 pro:DS-Red expression remains strongly localized to the inner integuments surrounding and opposite the micropylar end of the embryo sac. Expression in the outer integuments opposite the micropylar end of the embryo sac becomes more widespread and stronger. Expression continues to extend chalazally in the endothelium layer. FIG. 7A is a DIC image of an Arabidopsis ovule overlayed with a DS-RED fluorescence image; 7 B is DS-RED fluorescence and blue autofluorescence from the ovule; 7 C is a DIC image of an ovule (blue tinted) overlayed with a DS-RED fluorescence image. FIG. 8A is a DIC image of an ovule overlayed with a DS-RED fluorescence image; 8 B is DS-RED fluorescence and blue autofluorescence from the ovule; 8 C is a DIC image of an ovule (blue tinted) overlayed with a DS-RED fluorescence image.
FIGS. 9(A and B) demonstrates the expression pattern of a heterologous gene (DS-RED) operably linked to the promoter AT-CYP86C1 (PHP43541) in 2 different ovules at the late globular embryo stage. Expression is strong in the integuments opposite the micropylar end of the embryo sac. Expression can now be observed in the more chalazal portion of the endothelial cells. FIGS. 9A and B are fluorescent images showing DS-RED fluorescence expression and blue autofluorescence from the ovule.
FIGS. 10(A , B and C) demonstrates the expression pattern of a heterologous gene (DS-RED) operably linked to the promoter AT-CYP86C1 (PHP43541) in an ovule at the late globular embryo stage. FIG. 10A is a DIC image of an Arabidopsis ovule overlayed with a DS-RED fluorescence image; 10 B is DS-RED fluorescence and blue autofluorescence from the ovule; 10 C is a DIC image of an ovule (blue tinted) overlayed with a DS-RED fluorescence image.
FIG. 11(A-D) demonstrates the expression pattern of a heterologous gene (ZS-Green) operably linked to the promoter AT-PPM (putative pectin methylesterase, PHP48047) in ovules at the zygote stage. Two different patterns of expression were observed for the AT-PPM promoter: In the first pattern, (A and B), micropylar inner and outer integuments only, but not epidermal outer integument. In the second pattern (C and D), similar to pattern 1 plus expression throughout the inner integument surrounding the entire embryo sac, chalazal nucellus not included. FIGS. 11A and C are DIC images of an Arabidopsis ovule overlayed with a ZS-GREEN fluorescence images; 11 B and D are ZS-GREEN fluorescence and blue autofluorescence from the ovule.
FIG. 12(A-D) demonstrates the expression pattern of a heterologous gene (GUS) operably linked to the promoter AT-SLV3 (PHP43852) in Arabidopsis ovules at the megagametophyte (A and B) and zygote stages (C and D). The promoter AT SVL3 (AT3G20520) demonstrates expression early during megagametogenesis (A and B), at the four-nucleate megagametophyte stage expression is initially strong in the micropylar inner and outer integuments, spreading throughout the integuments of the entire ovule. By the zygote stage (C and D), the strength of expression has increased in the integumentary tissues. Also, the endosperm and embryo now show weak expression. Expression is absent in the funiculus. FIGS. 12A and C are color DIC images of cleared Arabidopsis ovules showing blue GUS staining. FIGS. 12B and D are the same ovules taken with bright-field optics in grayscale. Embryo sac=es.
FIG. 13(A-C) demonstrates the expression pattern of a heterologous gene (ZS-Green) operably linked to the promoter AT-EXT (endo-xyloglucan transferase, PHP 48049) in ovules at the egg/zygote stage. Expression is observed in the inner integuments and innermost layer of outer integument surrounding the micropylar end of the embryo sac (A and B), similar to NUC1. Occasionally, a single cell (innermost layer of outer integument) shows strong expression (C). FIG. 13A is a DIC image of an Arabidopsis ovule overlayed with a ZS-GREEN fluorescence image; 13 B and C are ZS-GREEN fluorescence and blue autofluorescence from the ovule.
FIGS. 14(A and B) demonstrates the expression pattern AT-NUC1pro::AT-RKD2-AT-DD45pro::DsRed (php50089) in an ovule. Reference example of normal embryo (red) development visualized via the AT-DD45-DsRed egg/early embryo reporter. FIG. 14A is a two-color fluorescence image of an Arabidopsis ovule, DsRed-positive globular embryo and blue autofluorescence from the ovule. FIG. 14B is a DIC image of the same ovule overlayed with a DS-Red fluorescence image of FIG. 14A .
FIG. 15 demonstrates the expression pattern AT-NUC1pro::AT-RKD2-AT-DD45pro::DsRed (php50089) in an ovule. At least one cell (red) in the outer integuments, outside of the embryo sac, shows an egg cell-like state expressing AT-DD45-DsRed. FIG. 15 is a two-color fluorescence image of an Arabidopsis ovule, AT-DD45-DsRed-positive egg-like cell and blue autofluorescence from the ovule.
FIG. 16 demonstrates the expression pattern AT-NUC1pro::AT-RKD2-AT-DD45pro::DsRed (php50089) in an ovule. Two or more cells at the micropylar base of the inner integument shows an egg cell-like state expressing AT-DD45-DsRed. FIG. 16A is a two-color fluorescence image of an Arabidopsis ovule, AT-DD45-DsRed-positive egg-like cell and blue autofluorescence from the ovule. FIG. 16B is a DIC image of the same ovule overlayed with a DS-Red fluorescence image of FIG. 16A .
FIG. 17 demonstrates the expression pattern AT-NUC1pro::AT-RKD2-AT-DD45pro::DsRed (php50089) in an ovule. Three enlarged cells of the inner integument show an embryo-like state expressing AT-DD45-DsRed. FIG. 17A is a two-color fluorescence image of an Arabidopsis ovule, AT-DD45-DsRed-positive egg-like cells and blue autofluorescence from the ovule.
FIG. 18 demonstrates the expression pattern AT-NUC1pro::AT-RKD2-AT-DD45pro::DsRed (php50089) in an ovule. Zygotic embryo within the embryo sac plus a single cell (arrow) expressing the egg marker (AT-DD45-DsRed) arising from an inner integumentary cell at the micropylar end of the ovule. FIG. 18 is a two-color fluorescence image of an Arabidopsis ovule, AT-DD45-DsRed-positive egg-like cell and blue autofluorescence from the ovule.
FIGS. 19(A and B) demonstrates the expression pattern AT-NUC1pro::AT-RKD2-AT-DD45pro::DsRed (php50089) in an Arabidopsis ovule. An early globular embryo-like structure shown developing outside of the embryo sac expressing AT-DD45-DsRed. FIG. 19A is a two-color fluorescence image, AT-DD45-DsRed-positive embryo and blue autofluorescence from the ovule. FIG. 19B is a DIC image of the same ovule overlayed with a DS-Red fluorescence image of FIG. 19A .
FIGS. 20(A and B) demonstrates the expression pattern AT-NUC1pro::AT-RKD2-AT-DD45pro::DsRed (php50089) in an Arabidopsis ovule. Zygotic embryo within the embryo sac plus an embryo-like group of cells (arrow) expressing the egg marker (AT-DD45-DsRed) arising from an inner integumentary cell at the micropylar end of the ovule. FIG. 20A is a two-color fluorescence image, AT-DD45-DsRed-positive zygotic embryo plus egg-like cells (arrow) and blue autofluorescence from the ovule. FIG. 20B is a DIC image of the same ovule overlayed with a DS-Red fluorescence image of FIG. 20A .
FIG. 21 demonstrates the expression pattern AT-NUC1pro::AT-RKD2-AT-DD45pro::DsRed (php50089) in an ovule. Globular-shaped embryo arising from the inner integuments and developing outside of the embryo sac. FIG. 21 is a three-color fluorescence image, AT-DD45-DsRed-positive embryo outside the embryo sac (arrow), grooen autofluorescence from the endothecial layer (innermost layer of the inner integument) and blue autofluorescence from the ovule.
FIG. 22 demonstrates the expression pattern AT-NUC1pro::AT-RKD2-AT-DD45pro::DsRed (php50089) in an Arabidopsis ovule. Young embryo-like body lying in an atypical position within the embryo sac, at the midway point, not at the normal micropylar end of the embryo sac. FIG. 22 is a two-color fluorescence image, AT-DD45-DsRed-positive embryo-like body and blue autofluorescence from the ovule.
FIG. 23 demonstrates the expression pattern AT-NUC1pro::AT-RKD2-AT-DD45pro::DsRed (php50089) in an ovule. Embryo-like body (red) arising from the integuments and developing outside of the embryo sac. FIG. 23 is a two-color fluorescence image, AT-DD45-DsRed-positive embryo-like body and blue autofluorescence from the ovule.
FIG. 24 demonstrates the expression pattern AT-CYP86C1PRO::AT-RKD2 AT-DD45::Ds-Red (PHP50088) in the integumentary cells of an ovule. Numerous cells of the inner and outer integuments show an egg cell-like state expressing the AT-DD45-DsRed egg cell-like identity marker. FIG. 24 is an image showing DS-RED fluorescence and blue autofluorescence from the Arabidopsis ovule.
FIG. 25 demonstrates the expression pattern AT-CYP86C1PRO::AT-RKD2 AT-DD45::Ds-Red (PHP50088). Two different planes of focus (left upper plane and right lower plane) within a single ovule showing embryogenic-like expression in outer and inner integumentary cells induced by RKD2 and fluorescently marked by AT-DD45-DsRed. FIGS. 25A and B are images showing DS-RED fluorescence and blue autofluorescence from the Arabidopsis ovule.
FIG. 26 demonstrates the expression pattern AT-CYP86C1PRO::AT-RKD2 AT-DD45::Ds-Red (PHP50088) in an ovule. Single inner integument cell at micropylar end showing egg/zygote-like identity, AT-DD45-DsRed. Inset is higher magnification of said single cell with AT-DD45::DsRed expression. FIG. 26A is an image showing the DS-RED fluorescence and blue autofluorescence from the ovule, 26 B is a DIC image of an ovule overlayed with a DS-RED fluorescence image.
FIG. 27 demonstrates the expression pattern AT-CYP86C1PRO::AT-RKD2 AT-DD45::Ds-Red (PHP50088) in an ovule with a single inner integumentary cell just outside of the embryo sac expressing the AT-DD45-DsRed marker. FIG. 27 is an image showing the DS-RED fluorescence and blue autofluorescence from the ovule.
FIG. 28(A-C) demonstrates the expression pattern AT-CYP86C1PRO::AT-RKD2 AT-DD45::Ds-Red(PHP50088) in a single ovule. Three to four adjacent integument cells all expressing the AT-DD45-DsRed marker. Middle cell of the group (arrow) has developed into a zygote-like structure that appears to have formed from the inner layer of the outer integument near the micropylar end of the ovule. This egg/zygote-like cell is densely cytoplasmic with a single large vacuole, and is morphologically similar to a normal egg cell or zygote, but outside the embryo sac. FIG. 28A is a DIC image of an ovule overlayed with a DS-RED fluorescence image; 28 B is DS-RED fluorescence and blue autofluorescence from the ovule. FIG. 28C is a higher magnification image of the AT-DD45-DsRed expressing cells showing the enlarged and densely cytoplamic egg/zygote-like cell.
FIG. 29 demonstrates the expression pattern AT-CYP86C1PRO::AT-RKD2 AT-DD45::Ds-Red (PHP50088) in an Arabidopsis ovule. Zygotic embryo (arrow) and two smaller bodies (arrowheads) centrally positioned within in the embryo sac, all expressing the egg/zygote cell-like marker AT-DD45-DsRed. FIG. 29 is a DS-RED fluorescence and blue ovular autofluorescence image.



DETAILED DESCRIPTION
The present disclosures now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the disclosures are shown. Indeed, these disclosures may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
Many modifications and other embodiments of the disclosures set forth herein will come to mind to one skilled in the art to which these disclosures pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the disclosures are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
I. Overview
Methods and compositions are provided which promote an egg cell-like state in an unreduced ovule plant cell that is outside of the embryo sac. As used herein, an “egg cell-like state” refers to an alteration in the phenotype of a non-egg cell such that it developed at least one or more characteristics found within an egg cell.
Egg cell-like state can be characterized by the development of an “egg cell-like transcriptional state” in an unreduced ovule plant cell. As used herein, an “egg cell-like transcriptional state” comprises any alteration of the gene expression profile of the unreduced ovule plant cell, such that the level of gene expression of least one or more genes of said unreduced ovule plant cell is altered and is reflective of the gene expression state found within an egg cell of the plant. Various methods can be used to assay for such a transition to an egg cell-like state. For example, egg cell-preferred promoters can be operably linked to a marker. Such a reporter construct would be inactive in the unreduced ovule plant cell found outside the embryo sac, but the reporter construct would become active upon the formation of the egg cell-like state. Egg cell-preferred promoters which can be used to detect an egg cell-like transcriptional state include, for example, the Arabidopsis thaliana RKD1 transcription factor promoter (AT-RKD1 PRO; SEQ ID NO: 21); the Arabidopsis thaliana RKD2 transcription factor promoter (AT-RKD2 PRO; SEQ ID NO: 22); down regulated in dif1 (determinant infertile1)1 promoter (AT-DD45 PRO; SEQ ID NO: 10); and the EASE promoter (egg apparatus preferred enhancer promoter; SEQ ID NO: 19). See, also, Yang, et al., (2005) Plant Physiology 139:1421-1432. See also, U.S. Provisional Application Ser. No. ______, entitled Ovule Specific Promoters and Methods of Their Use, filed concurrently herewith and herein incorporated by reference in its entirety. When employing such egg cell-preferred promoters operably linked to an appropriate marker one can assay for an egg-like transcriptional state by assaying for expression of the marker in unreduced cells outside of the embryo sac. In this manner, an egg cell-like state can be assayed for in tissues of the plant ovule including any tissues and substructures suitable for adventitious embryony.
Additional female gametophyte-specific marker genes that can be monitored to assay for an egg cell-like state include any female gametophyte-preferred expressed genes, such as, AT1G18770 (MYB98), AT1G26795 (Self incompatibility protein-related), AT2G20070, at4g25530 (homeobox protein, fwa) and at5g40260 (nodulin mtN3 family protein). See, for example, Koszegi, et al., (2011) Plant Journal 67:280-291, which herein incorporated by reference.
In another embodiment, an egg cell-like state may be indicated through the development of a cellular morphological state like that of an egg, notably the polar distribution of dense cytoplasm occupying much of the cell volume with a nucleus located at the densely cytoplasmic apical end of the cell opposite a large vacuole which occupies a medial to basal position within the cell. One embodiment would include an Arabidopsis cell similar to the natural egg cell size of approximately 26 μm tall×15 μm wide. Such morphological embodiments are supplementary to molecular determinants and would not be diagnostic of an egg cell-like state independent from other determinants.
In still other embodiments, an egg cell-like state can be characterized and assayed for the development of embryo-like structures in tissues and substructures outside of the embryo sac, including the formation of such structures in any tissues and substructures suitable for adventitious embryony. An embryo-like state can be characterized by a contiguous grouping of cells displaying the morphological developmental states of an embryo. Morphological characteristics of an embryo-like state may include typically vacuolated cells becoming densely cytoplasmic or isodiametric cells becoming elongate and egg- or zygote-shaped. Other cytological features suggestive of an egg-like state may include changes in polarity of the cell, the “apex” becoming broad while the “base” becomes attenuated and tapered. Other features may include the majority of the cell's cytoplasm occupying an apical position while a large vacuole occupies a medial to basal position within the cell. The nucleus of this egg-like cell would occupy an apical position within the cell. In the example of Arabidopsis, the morphological states would be an egg, zygote, proembryo, globular, or heart-shaped embryo, torpedo, walking stick and curled cotyledon. Development of a suspensor or cotyledon(s) would be another morphological embodiment. Such structures may also express molecular markers such as the expression of AT-DD45 up to the early globular stage. Later globular stage through maturity, the embryo-like structures may express a KTI3 reporter or other embryo specific marker expression.
In specific embodiments, the “egg cell-like state” can progress into the creation of adventitious embryony or partial embryony. Such methods and compositions are discussed in further detail elsewhere herein. In adventitious embryony (sporophytic apomixis), an embryo is formed directly out of the somatic tissue within the ovule that is outside of the embryo sac. In other words, the embryo is not from a gametophyte, but rather is formed, for example, from the nucellus and/or integument tissue. In incomplete embryony, embryo development is incomplete. In some embodiments this may indicate a lack of a suspensor. In other embodiments this may indicate an arrest in embryo development prior to maturation. In yet other embodiments, this may indicate a lack of a globular head, cotyledon or other embryo organ.








TABLE 1






POLYNUCLEOTIDE/




POLYPEPTIDE

SEQ ID.
NAME
DESCRIPTION
(PN/PP)



SEQ ID NO: 1
AT-NUC1 PRO
OVULE TISSUE-
PN


(AT4G21620)
PREFERRED



PROMOTER

SEQ ID NO: 2
ALT-AT-NUC1
OVULE TISSUE-
PN


PRO
PREFERRED


(AT4G21620)
PROMOTER

SEQ ID NO: 3
AT-CYP86C1
OVULE TISSUE-
PN


(AT1G24540)
PREFERRED



PROMOTER

SEQ ID NO: 4
ALT-AT-
OVULE TISSUE-
PN


CYP86C1
PREFERRED



PROMOTER

SEQ ID NO: 5
AT-PPM1 PRO
OVULE TISSUE-
PN


AT5G49180
PREFERRED



PROMOTER

SEQ ID NO: 6
AT-EXT PRO
OVULE TISSUE-
PN


AT3G48580
PREFERRED



PROMOTER

SEQ ID NO: 7
AT-GILT1 PRO
OVULE TISSUE-
PN


AT4G12890
PREFERRED



PROMOTER

SEQ ID NO: 8
AT-TT2 PRO
OVULE TISSUE-
PN


AT5G35550
PREFERRED



PROMOTER

SEQ ID NO: 9
AT-SVL3 PRO
OVULE TISSUE-
PN



PREFERRED



PROMOTER

SEQ ID NO: 10
AT-DD45 PRO
EGG CELL-PREFERRED
PN



PROMOTER

SEQ ID NO: 11
ATRKD1
CDNA OF RKD
PN


FULL LENGTH
POLYPEPTIDE


CDNA

SEQ ID NO: 12
ATRKD1
RKD POLYPEPTIDE
PP


AMINO ACID


NM_101737.1

SEQ ID NO: 13
ATRKD2
CDNA OF RKD
PN


(AT1G74480)
POLYPEPTIDE


FULL LENGTH


CDNA


NM_106108

SEQ ID NO: 14
ATRKD2
RKD POLYPEPTIDE
PP


(AT1G74480)


AMINO ACID

SEQ ID NO: 15
ATRKD3
CDNA OF RKD
PN


(AT5G66990)
POLYPEPTIDE


FULL LENGTH


CDNA


NM_126099

SEQ ID NO: 16
ATRKD3
RKD POLYPEPTIDE
PP


(AT5G66990)


AMINO ACID


NP_201500.1

SEQ ID NO: 17
ATRKD4
CDNA OF RKD
PN


(AT5G53040)
POLYPEPTIDE


FULL LENGTH


CDNA

SEQ ID NO: 18
ATRKD4
RKD POLYPEPTIDE
PP


(AT5G53040)


AMINO ACID


NP_200116.1

SEQ ID NO: 19
EASE PRO
EGG CELL-PREFERRED
PN



PROMOTER

SEQ ID NO: 20
AT-DD2 PRO
EGG CELL-PREFERRED
PN



PROMOTER

SEQ ID NO: 21
AT-RKD1 PRO
EGG CELL-PREFERRED
PN

SEQ ID NO: 22
AT-RKD2 PRO
EGG CELL-PREFERRED
PN

SEQ ID NO: 23
BA-BARNASE-
DNA ENCODING
PN


INT
CYTOTOXIC



POLYPEPTIDE

SEQ ID NO: 24
DAM
DNA ENCODING
PN


METHYLASE
CYTOTOXIC



POLYPEPTIDE

SEQ ID NO: 25
DMETH N-TERM
OLIGONUCLEOTIDE
PN

SEQ ID NO: 26
INTE-N
OLIGONUCLEOTIDE
PN

SEQ ID NO: 27
INTE-C
OLIGONUCLEOTIDE
PN

SEQ ID NO: 28
DMETH C-TERM
OLIGONUCLEOTIDE
PN

SEQ ID NO: 29
ADP
DNA ENCODING
PN


RIBOSYLASE
CTYOTOXIC



POLYPEPTIDE

SEQ ID NO: 30
FEM2
EMBRYO SAC-
PN



PREFERRED



PROMOTER

SEQ ID NO: 31
ATRKD5
CDNA OF RKD
PN


AT4G35590; DNA;
POLYPEPTIDE



ARABIDOPSIS




THALIANA


SEQ ID NO: 32
AT-
RKD POLYPEPTIDE
PP


RKD5; PRT; ARABIDOPSIS



THALIANA


SEQ ID NO: 33
AT1G24540
OVULE TISSUE-
PN


AT-CP450-1 PRO
PREFERRED



PROMOTER

SEQ ID NO: 34
ZMDD45PRO;
PROMOTER
PN


DNA; ZEA MAYS

SEQ ID NO: 35
PCO659480
OLIGONUCLEOTIDE
PN


5PRIMELONG;


DNA; ZEA MAYS

SEQ ID NO: 36
PCO659480
OLIGONUCLEOTIDE
PN


3PRIMELONG;


DNA; ZEA MAYS

SEQ ID NO: 37
ZSGREEN5PRIME;
OLIGONUCLEOTIDE
PN


DNA;


ZOANTHUS SP

SEQ ID NO: 38
ZSGREEN3PRIME;
OLIGONUCLEOTIDE
PN


DNA;


ZOANTHUS SP

SEQ ID NO: 39
CYAN1 5PRIME;
OLIGONUCLEOTIDE
PN


DNA; ANEMONIA



MAJANO


SEQ ID NO: 40
CYAN1 3PRIME;
OLIGONUCLEOTIDE
PN


DNA; ANEMONIA



MAJANO


SEQ ID NO: 41
AT-DD1 PRO;
PROMOTER
PN


DNA;



ARABIDOPSIS




THALIANA


SEQ ID NO: 42
AT-DD31 PRO;
PROMOTER
PN


DNA;



ARABIDOPSIS




THALIANA


SEQ ID NO: 43
AT-DD65 PRO;
PROMOTER
PN


DNA;



ARABIDOPSIS




THALIANA


SEQ ID NO: 44

SORGHUM

PROMOTER-OVULE
PN


BICOLOR OVULE


SPECIFIC


PROMOTER 1


(SB10G008120.1)

SEQ ID NO: 45
PROMOTER
PROMOTER-OVULE
PN


RICE OVULE


CANDIDATE 1


(OS02G-51090)

SEQ ID NO: 46
AT-RKD2 PRO
PROMOTER WITH
PN


(AT1G74480)
PROPOSED TETOP



SITES. OPTION 1

SEQ ID NO: 47
AT-RKD2 PRO
PROMOTER WITH
PN


(AT1G74480)
PROPOSED TETOP



SITES. OPTION 2

SEQ ID NO: 48
AT-RKD2 PRO
PROMOTER WITH
PN


(AT1G74480)
PROPOSED TETOP



SITES. OPTION 3

SEQ ID NO: 49
BA-BASTAR;
CYTOTOXIC COGNATE
PN


DNA; BACILLUS
REPRESSOR



AMYLOLIQUEFACIENS


SEQ ID NO: 50
AT-RKD3 PRO;
PROMOTER
PN


DNA;



ARABIDOPSIS




THALIANA


SEQ ID NO: 51
AT-RKD4 PRO;
PROMOTER
PN


DNA;



ARABIDOPSIS




THALIANA


SEQ ID NO: 52
AT-RKD5 PRO;
PROMOTER
PN


DNA;



ARABIDOPSIS




THALIANA


SEQ ID NO: 53
AT-LAT52LP1
PROMOTER
PN


PRO; DNA;



ARABIDOPSIS




THALIANA


SEQ ID NO: 54
AT-LAT52LP2
PROMOTER
PN


PRO; DNA;



ARABIDOPSIS




THALIANA


SEQ ID NO: 55
AT-PPG1 PRO;
PROMOTER
PN


DNA;



ARABIDOPSIS




THALIANA


SEQ ID NO: 56
AT-PPG2 PRO;
PROMOTER
PN


DNA;



ARABIDOPSIS




THALIANA
































































































































































































II. Sequences Encoding RKD Polypeptides
Methods and compositions are provided which promote an egg cell-like state in an unreduced ovule plant cell that is outside of the embryo sac. The egg cell-like state is produced in the unreduced ovule plant cell by increasing the expression of at least one RKD polypeptide in an unreduced ovule plant cell that is not in the embryo sac.
As used herein, “RKD” or “RWP-RK Domain-containing” polypeptide refers to a class of proteins that function as regulators of egg cell related gene expression programs and comprises a RWP-RK domain. RKD proteins are functionally analogous to the basic motif of bZIP transcription factors. The structures of various RKD polypeptides are known, and the RKD genes have been identified in a variety of plants including Selaginella sp., Vitis vinifera, Populus sp., Oryza sativa, Zea mays and Hordum vulgare . For example, the RKD family of Arabidopsis comprises at least five members: AtRKD1 (Atg18790), AtRKD2 (At1g74480), AtRKD3 (At5g66990), AtRKD4 (At5g53040) and AtRKD5 (At4g35590). See, FIG. 1 which provides an alignment of known RKD polypeptides from Arabidopsis and wheat. Various methods and compositions are provided which employ polynucleotides and polypeptides having RKD activity. Such RKD polypeptides include those set forth in any one of SEQ ID NO: 12, 14, 16, 18 and 32 and biologically active variants and fragments thereof. Further provided are the polynucleotides (SEQ ID NO: 11, 13, 15, 17 and 31) encoding these various polypeptides and active variant and fragments thereof.
As used herein, “RKD activity” comprises a polypeptide that regulates egg cell gene expression. As used herein, a polypeptide having “RKD activity” comprises an RKD polypeptide or an active variant or fragment thereof that retains sufficient RKD activity such that (i) said polypeptide has transcriptional regulatory activity; (ii) said polypeptide when expressed at sufficient levels in an unreduced ovule plant cell alters the transcriptional state to an egg cell-like transcriptional state and/or (iii) said polypeptide when expressed in a host plant cell increases expression of a marker gene operably linked to an egg cell promoter including, for example, an egg cell-preferred promoter comprising At1g60530, At3g63320, At1g66610, or AT1g53930 or other egg cell-preferred promoters disclosed elsewhere herein. Methods to assay for such activity are known. See, for example, Koszegi, et al., (2011) Plant Journal Accelerated article, doi: 101111/j.1365-313x.2011.04592.x, which herein incorporated by reference. Non-limiting examples of female gametophyte-specific marker genes which are expressed in an egg cell-like transcriptional state include, but are not limited to, female gametophyte specific expressed genes AT1G18770 (MYB98), AT1G26795 (Self incompatibility protein-related), AT2G20070 (unknown), at4g25530 (homoebox protein, fwa) and at5g40260 (nodulin mtN3 family protein). See, Koszegi, et al., (2011) Plant Journal Accelerated article, doi:101111/j.1365-313x.2011.04592.x.
As used herein, an “isolated” or “purified” polynucleotide or polypeptide, or biologically active portion thereof, is substantially or essentially free from components that normally accompany or interact with the polynucleotide or polypeptide as found in its naturally occurring environment. Thus, an isolated or purified polynucleotide or polypeptide is substantially free of other cellular material or culture medium when produced by recombinant techniques, or substantially free of chemical precursors or other chemicals when chemically synthesized. Optimally, an “isolated” polynucleotide is free of sequences (optimally protein encoding sequences) that naturally flank the polynucleotide (i.e., sequences located at the 5′ and 3′ ends of the polynucleotide) in the genomic DNA of the organism from which the polynucleotide is derived. For example, in various embodiments, the isolated polynucleotide can contain less than about 5 kb, 4 kb, 3 kb, 2 kb, 1 kb, 0.5 kb, or 0.1 kb of nucleotide sequence that naturally flank the polynucleotide in genomic DNA of the cell from which the polynucleotide is derived. A polypeptide that is substantially free of cellular material includes preparations of polypeptides having less than about 30%, 20%, 10%, 5%, or 1% (by dry weight) of contaminating protein. When the polypeptide of the disclosure or biologically active portion thereof is recombinantly produced, optimally culture medium represents less than about 30%, 20%, 10%, 5%, or 1% (by dry weight) of chemical precursors or non-protein-of-interest chemicals.
As used herein, polynucleotide or polypeptide is “recombinant” when it is artificial or engineered or derived from an artificial or engineered protein or nucleic acid. For example, a polynucleotide that is inserted into a vector or any other heterologous location, e.g., in a genome of a recombinant organism, such that it is not associated with nucleotide sequences that normally flank the polynucleotide as it is found in nature is a recombinant polynucleotide. A polypeptide expressed in vitro or in vivo from a recombinant polynucleotide is an example of a recombinant polypeptide. Likewise, a polynucleotide sequence that does not appear in nature, for example, a variant of a naturally occurring gene is recombinant.
A “control” or “control plant” or “control plant cell” provides a reference point for measuring changes in phenotype of the subject plant or plant cell and may be any suitable plant or plant cell. A control plant or plant cell may comprise, for example: (a) a wild-type or native plant or cell, i.e., of the same genotype as the starting material for the genetic alteration which resulted in the subject plant or cell; (b) a plant or plant cell of the same genotype as the starting material but which has been transformed with a null construct (i.e., with a construct which has no known effect on the trait of interest, such as a construct comprising a marker gene); (c) a plant or plant cell which is a non-transformed segregant among progeny of a subject plant or plant cell; (d) a plant or plant cell which is genetically identical to the subject plant or plant cell but which is not exposed to the same treatment (e.g., herbicide treatment) as the subject plant or plant cell or (e) the subject plant or plant cell itself, under conditions in which the gene of interest is not expressed.
A. Active Fragments and Variants of RKD Sequences
As discussed above, methods and compositions are provided which employ polynucleotides and polypeptides having RKD activity. Fragments and variants of RKD polynucleotides and polypeptides are also encompassed. By “fragment” is intended a portion of the polynucleotide or a portion of the amino acid sequence and hence protein encoded thereby. Fragments of a polynucleotide may encode protein fragments that retain RKD activity. Thus, fragments of a nucleotide sequence may range from at least about 20 nucleotides, about 50 nucleotides, about 100 nucleotides and up to the full-length polynucleotide encoding the RKD polypeptides.
A fragment of an RKD polynucleotide that encodes a biologically active portion of an RKD protein will encode at least 50, 75, 100, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400, 410, 415, 420, 425, 430, 435 or 440 contiguous amino acids or up to the total number of amino acids present in a full-length RKD polypeptide.
Thus, a fragment of an RKD polynucleotide may encode a biologically active portion of an RKD polypeptide. A biologically active portion of an RKD polypeptide can be prepared by isolating a portion of one of the RKD polynucleotides, expressing the encoded portion of the RKD polypeptides (e.g., by recombinant expression in vitro) and assessing the activity of the RKD portion of the RKD protein. Polynucleotides that are fragments of an RKD nucleotide sequence comprise at least 16, 20, 50, 75, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 800, 900, 1,000, 1,100, 1,200, 1,300 or 1,400 contiguous nucleotides or up to the number of nucleotides present in a full-length RKD polynucleotide disclosed herein.
“Variant” protein is intended to mean a protein derived from the protein by deletion (i.e., truncation at the 5′ and/or 3′ end) and/or a deletion or addition of one or more amino acids at one or more internal sites in the native protein and/or substitution of one or more amino acids at one or more sites in the native protein. Variant proteins encompassed are biologically active, that is they continue to possess the desired biological activity of the native protein, that is, have RKD activity. Such variants may result from, for example, genetic polymorphism or from human manipulation.
“Variants” is intended to mean substantially similar sequences. For polynucleotides, a variant comprises a polynucleotide having a deletion (i.e., truncations) at the 5′ and/or 3′ end and/or a deletion and/or addition of one or more nucleotides at one or more internal sites within the native polynucleotide and/or a substitution of one or more nucleotides at one or more sites in the native polynucleotide. As used herein, a “native” polynucleotide or polypeptide comprises a naturally occurring nucleotide sequence or amino acid sequence, respectively. For polynucleotides, conservative variants include those sequences that, because of the degeneracy of the genetic code, encode the amino acid sequence of one of the RKD polypeptides. Naturally occurring variants such as these can be identified with the use of well-known molecular biology techniques, as, for example, with polymerase chain reaction (PCR) and hybridization techniques as outlined below. Variant polynucleotides also include synthetically derived polynucleotides, such as those generated, for example, by using site-directed mutagenesis or gene synthesis but which still encode an RKD polypeptide.
Biologically active variants of an RKD polypeptide (and the polynucleotide encoding the same) will have at least about 70%. 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more sequence identity to any RKD polypeptide, including the polypeptide of any one of SEQ ID NO: 12, 14, 16, 18 and 32 as determined by sequence alignment programs and parameters described elsewhere herein.
Biologically active variants of an RKD polynucleotide will have at least about 70%. 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more sequence identity to any polynucleotide encoding an RKD polypeptide, including the polynucleotide of any one of SEQ ID NO: 11, 13, 15, 17 or 31 as determined by sequence alignment programs and parameters described elsewhere herein.
The RKD polypeptide and the active variants and fragments thereof may be altered in various ways including amino acid substitutions, deletions, truncations and insertions. Methods for such manipulations are generally known in the art. For example, amino acid sequence variants and fragments of the RKD proteins can be prepared by mutations in the DNA. Methods for mutagenesis and polynucleotide alterations are well known in the art. See, for example, Kunkel, (1985) Proc. Natl. Acad. Sci. USA 82:488-492; Kunkel, et al., (1987) Methods in Enzymol. 154:367-382; U.S. Pat. No. 4,873,192; Walker and Gaastra, eds. (1983) Techniques in Molecular Biology (MacMillan Publishing Company, New York) and the references cited therein. Guidance as to appropriate amino acid substitutions that do not affect biological activity of the protein of interest may be found in the model of Dayhoff, et al., (1978) Atlas of Protein Sequence and Structure (Natl. Biomed. Res. Found., Washington, D.C.), herein incorporated by reference. Conservative substitutions, such as exchanging one amino acid with another having similar properties, may be optimal.
Obviously, the mutations that will be made in the DNA encoding the variant must not place the sequence out of reading frame and optimally will not create complementary regions that could produce secondary mRNA structure. See, EP Patent Application Publication Number 75,444.
Variant polynucleotides and proteins also encompass sequences and proteins derived from a mutagenic and recombinogenic procedure such as DNA shuffling. With such a procedure, one or more different RDK coding sequences can be manipulated to create a new RKD polypeptide possessing the desired properties. In this manner, libraries of recombinant polynucleotides are generated from a population of related sequence polynucleotides comprising sequence regions that have substantial sequence identity and can be homologously recombined in vitro or in vivo. For example, using this approach, sequence motifs encoding a domain of interest may be shuffled between the RKD sequences disclosed herein and other known RKD genes to obtain a new gene coding for a protein with an improved property of interest, such as a decreased K m in the case of an enzyme. Strategies for such DNA shuffling are known in the art. See, for example, Stemmer, (1994) Proc. Natl. Acad. Sci. USA 91:10747-10751; Stemmer, (1994) Nature 370:389-391; Crameri, et al., (1997) Nature Biotech. 15:436-438; Moore, et al., (1997) J. Mol. Biol. 272:336-347; Zhang, et al., (1997) Proc. Natl. Acad. Sci. USA 94:4504-4509; Crameri, et al., (1998) Nature 391:288-291 and U.S. Pat. Nos. 5,605,793 and 5,837,458.
III. Ovule Tissue-Preferred Promoters
In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. Early in development, it consists of three parts: the integument forming its outer layer, the nucellus (or megasporangium) and the funiculus. The nucellus produces the megasporocyte which will undergo meiosis to form the megaspores during megasporogenesis. In the Polygonum -type of embryo sac development, three of the megaspores degrade and one becomes the functional megaspore. During megagametogenesis, the functional megaspore (in Polygonum -type embryo sacs) goes through three rounds of syncytial mitoses to become an eight-nucleate cell. Cellularization occurs during further development to produce a mature embryo sac which includes an egg, synergids, antipodals, and the central cell with two polar nuclei in the typical Polygonum -type of embryo sac development. In some species ( Zea spp.), antipodals can further divide and become numerous. Thus, as used herein, the ovule is initially composed of unreduced tissue that gives rise to the haploid tissue of the female gametophyte. The female gametophyte further develops into the “mature egg sac”, comprised of four unique cell types: one egg cell, a central cell, two synergids and three or more antipodal cells.
Various types of promoters can be employed in the methods and compositions provided herein. Promoters can drive expression in a manner that is cell-type-preferred, cell-type-specific, tissue-preferred or tissue-specific. Examples of promoters under developmental control include promoters that preferentially initiate transcription in certain tissues, such as leaves, roots, seeds or ovules. Such promoters are referred to as “tissue preferred”. Promoters which initiate transcription only in certain tissue are referred to as “tissue specific”. A “cell type” preferred promoter primarily drives expression in certain cell types in one or more organs, for example, vascular cells in roots, leaves, or ovules. An “inducible” or “repressible” promoter is a promoter which is under environmental control. Examples of environmental conditions that may affect transcription by inducible promoters include anaerobic conditions or the presence of light. Tissue specific, tissue preferred, cell type specific, cell type preferred and inducible promoters constitute the class of “non-constitutive” promoters. A “constitutive” promoter is a promoter which is active under most environmental conditions.
As used herein, an “ovule tissue-preferred promoter” comprises a promoter that is predominately active in at least one or all of the unreduced ovule tissues of the plant, including for example, the integuments and nucellus, when compared to its level of expression when not operably linked to the ovule tissue-preferred promoter. Thus, while some level of expression of an operably linked heterologous nucleotide sequence may occur in other plant tissue types, expression occurs most abundantly in the ovule somatic tissue.
In specific embodiments, an ovule tissue-preferred promoter is employed which is “active in at least one non-gametophyte tissue in a plant ovule”. Such a promoter will be active in a somatic unreduced cell of the plant ovule that is outside of the embryo sac. Such a promoter may be active only in non-gametophyte tissue of the ovule or, alternatively, the promoter can show activity in the gametophytic tissue in addition to at least one other ovule tissue/structure. Non-limiting examples of promoters capable of directing expression in this manner include, the Arabidopsis NUC1 promoter region as set forth in SEQ ID NO: 1 or 2; the Arabidopsis CYP86C1 promoter region as set forth in SEQ ID NO: 3 or 4; the Arabidopsis PPM1 promoter region as set forth in SEQ ID NO: 5; the Arabidopsis EXT promoter region is set forth in SEQ ID NO: 6; the Arabidopsis GILT1 promoter region as forth in SEQ ID NO: 7; the Arabidopsis TT2 promoter region as forth in SEQ ID NO: 8; the Arabidopsis SLV3 promoter region as forth in SEQ ID NO: 9 and the Arabidopsis promoter AT1G24540 (AT-CP450-1-PRO) as set forth in SEQ ID NO: 33 or active variants and fragments thereof. In specific embodiments, the promoter employed is an ovule-specific promoter.
The promoter AT NUC1 (AT4G21620; GenBank: CP002687.1 (bps. 11496827-11495501), GENE ID: 828249; also known as F17L22.80; F17L22 — 80; SEQ ID NO: 1 and 2) promoter demonstrates an expression pattern in the micropylar tip of the inner integument prior to fertilization. Expression further spreads chalazally through the inner integuments to surround the micropylar half of the embryo sac. Later in development, expression transitions from the micropylar inner integuments to the chalazal integuments. Expression appears present from several days before pollination to several days after pollination. At the heart-shaped embryo stage, expression is observed only at the integuments opposite the chalazal end. FIG. 1 provides the expression pattern of the AT NUC1 promoter. See also, US Patent Application Publication 2011/0107458 A1, herein incorporated by reference.
The promoter AT CYP86C1 (AT1G24540; GenBank: CP002684.1 (bps 8697732-8699750; Other names: F21J9.20; SEQ ID NO: 3 or 4) displays an expression pattern in the micropylar tip of the inner integument prior to fertilization. Expression spreads chalazally through the endothelium (innermost layer of the inner integument) to surround the micropylar base of the embryo sac and expression then spreads chalazally through the entire endothelial layer. Expression appears present from several days before pollination to several days after pollination. FIGS. 2 through 10 provide the expression pattern of the CYP86C1 promoter.
The promoter AT PPM1 (AT5G49180; GenBank: CP002688.1 (bps 19943368-19942879; other names: K21P3.5, K21P3 — 5; SEQ ID NO: 5) demonstrates two types of expression patterns. First the AT PPM1 promoter demonstrates an expression pattern in the micropylar inner and outer integuments, but not the epidermal layer of the outer integument. The second type, of expression pattern is in the micropylar inner and outer integuments, as above, but expression extends chalazally through the inner and outer integuments (not epidermal layer) to surround the entire embryo sac, with the exception of the chalazal nucellus. No expression was observed within the embryo sac. FIG. 11 provides the expression pattern of the AT PPM1 promoter. See also, U.S. Pat. No. 7,179,904, U.S. Pat. No. 7,402,667, WO 2006/005023, WO 2006/066134, WO 2006/076099, WO 2007/075172, WO 2007/078286 and WO 2006/08102 and Louvet, et al., (2006) Planta 224:782-791, each of which is herein incorporated by reference.
The promoter AT SVL3 (AT3G20520; GenBank Accession NM — 112944; also known as K10D20.6, SHV3-LIKE 3, SVL3; SEQ ID NO: 9) demonstrates an expression pattern that starts early during megagametogenesis. At the four nucleate megagametophyte stage, expression is initially strong in the micropylar inner and outer integuments spreading throughout the integuments of the entire ovule. Later in development, zygote stage, the endosperm and embryo also show expression. Thus, expression could be noted throughout the entire ovule with the exception of the funiculus. FIG. 12 provides the expression pattern for the AT-SVL3 promoter. Prior expression data is limited to expression in 6-week old siliques. See, Hayashi, et al., (2008) Plant Cell Physiol. 49:1522-1535, herein incorporated by reference.
The promoter AT EXT (AT3G48580; Genbank CP002686.1, bps 18004981-18007235; also known as T8P19.90, XTH11, XYLOGLUCAN ENDO-TRANSGLUCOSYLASE/HYDROLASE 11; SEQ ID NO: 6) demonstrates an expression pattern in the inner integuments and innermost layer of the outer integument surrounding the micropylar end of the embryo sac. In addition, in one example, a single cell (innermost layer of outer integument) shows strong expression. The expression pattern for AT EXT is shown in FIG. 13 .
Additional ovule tissue-preferred promoters that are active in at least one non-gametophyte tissue in a plant ovule include the promoter AT GILT1 (SEQ ID NO: 7; AT4G12890; Genbank CP002686.1 (bps 7545227-7546409); other names: T20K18.240, T20K18-240. See also, U.S. Pat. No. 7,179,904, U.S. Pat. No. 7,402,667, U.S. Pat. No. 7,169,915, WO 2006/005023, WO 2006/066134, WO 2006/076099, WO 2007/075172, WO 2007/078286, WO 2006/081029 and WO 2002/016655 and Lovet, et al., (2006) Planta 224:782-791. Additional promoters include, AT TT2 (SEQ ID NO: 8; AT5G35550; GenBank Accession AJ299452; also known as Transparent Testa 2, ATMYB123, AT TT2, MOK9.18, MOK9 — 18, MYB DOMAIN PROTEIN 123, MYB123, TT2). See also, WO 2006/031779; U.S. Pat. No. 6,972,197; WO 2000/055325 and Gonzalez, et al., (2009) Developmental Bio 352(2):412-421. Further promoters include the Arabidopsis promoter AT1G24540 as set forth in SEQ ID NO: 33 or active variants and fragments thereof.
Thus, the methods and compositions include isolated polynucleotides comprising the ovule tissue-preferred promoters disclosed above, and also any ovule tissue-preferred promoter that is active in at least one non-gametophyte tissue in a plant ovule. Such sequences include the promoter nucleotide sequences set forth in SEQ ID NOS: 1, 2, 3, 4, 5, 6, 7, 8, 9 or 33. By “promoter” is intended a regulatory region of DNA usually comprising a TATA box capable of directing RNA polymerase II to initiate RNA synthesis at the appropriate transcription initiation site for a particular polynucleotide sequence. A promoter may additionally comprise other recognition sequences generally positioned upstream or 5′ to the TATA box, referred to as upstream promoter elements, which influence the transcription initiation rate. The promoter sequences disclosed herein regulate (i.e., activate) transcription from the promoter region.
It is recognized that additional domains can be added to the promoter sequences disclosed herein and thereby modulate the level of expression, the developmental timing of expression, or tissue type that expression occurs in. See particularly, Australian Patent Number AU-A-77751/94 and U.S. Pat. Nos. 5,466,785 and 5,635,618.
Fragments and variants of each of the ovule tissue-preferred promoter polynucleotides are further provided. Fragments of a promoter polynucleotide may retain biological activity and hence retain transcriptional regulatory activity. Thus, fragments of a promoter nucleotide sequence may range from at least about 20 nucleotides, about 50 nucleotides, about 100 nucleotides and up to the full-length polynucleotide of the disclosure. Thus, a fragment of an ovule tissue-preferred promoter polynucleotide may encode a biologically active portion of an ovule tissue-preferred promoter. A biologically active portion of an ovule tissue-preferred promoter polynucleotide can be prepared by isolating a portion of one of the ovule tissue-preferred promoter polynucleotides and assessing the activity of the portion of the ovule tissue-preferred promoter. Polynucleotides that are fragments of an ovule tissue-preferred polynucleotide comprise at least 16, 20, 50, 75, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 800, 900, 1,000, 1,100, 1,200, 1,300, 1,400, 1,500, 1,600, 1,700, 1,800, 1,900, 2000, nucleotides or up to the number of nucleotides present in a full-length ovule tissue-preferred promoter polynucleotide disclosed herein.
For a promoter polynucleotide, a variant comprises a deletion and/or addition of one or more nucleotides at one or more internal sites within the native polynucleotide and/or a substitution of one or more nucleotides at one or more sites in the native polynucleotide. Generally, variants of a particular ovule tissue-preferred promoter will have at least about 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more sequence identity to that particular polynucleotide as determined by sequence alignment programs and parameters described elsewhere herein.
Any of the promoter sequences employed herein can be modified to provide for a range of expression levels of the heterologous nucleotide sequence. Thus, less than the entire promoter region may be utilized and the ability to drive expression of the nucleotide sequence of interest retained. It is recognized that expression levels of the mRNA may be altered in different ways with deletions of portions of the promoter sequences. The mRNA expression levels may be decreased, or alternatively, expression may be increased as a result of promoter deletions if, for example, there is a negative regulatory element (for a repressor) that is removed during the truncation process. Generally, at least about 20 nucleotides of an isolated promoter sequence will be used to drive expression of a nucleotide sequence.
Variant polynucleotides also encompass sequences derived from a mutagenic and recombinagenic procedure such as DNA shuffling. With such a procedure, one or more different promoter sequences can be manipulated to create a new ovule tissue-preferred promoter possessing the desired properties. Strategies for such DNA shuffling are described elsewhere herein.
Methods are available in the art for determining if a promoter sequence retains the ability to regulate transcription in the desired temporal and spatial pattern. Such activity can be measured by Northern blot analysis. See, for example, Sambrook, et al., (1989) Molecular Cloning: A Laboratory Manual (2d ed., Cold Spring Harbor Laboratory Press, Plainview, N.Y.), herein incorporated by reference. Alternatively, biological activity of the promoter can be measured using assays specifically designed for measuring the activity and or level of the polypeptide being expressed from the promoter. Such assays are known in the art.
IV. Expression Constructs
Methods and compositions are provided to increase the activity/level of an RKD polypeptide in an unreduced ovule plant cell that is outside of the embryo sac. In specific embodiments, such modulation of activity/level of the RKD polypeptide promotes an egg cell-like state in an unreduced ovule plant cell that is outside of the embryo sac. Such methods and compositions can employ an expression construct comprising a RKD polypeptide or active variant or fragment thereof operably linked to an ovule tissue-preferred promoter, in particular an ovule tissue-preferred promoter that is active in at least one non-gametophyte tissue in a plant ovule and is active in an unreduced cell that is outside of the embryo sac.
The expression cassette can include 5′ and 3′ regulatory sequences operably linked to the RKD-encoding polynucleotide or an active variant or fragment thereof. “Operably linked” is intended to mean a functional linkage between two or more elements. For example, an operable linkage between a polynucleotide of interest and a regulatory sequence (i.e., a promoter) is functional link that allows for expression of the polynucleotide of interest. Operably linked elements may be contiguous or non-contiguous. When used to refer to the joining of two protein coding regions, by operably linked is intended that the coding regions are in the same reading frame. The cassette may additionally contain at least one additional gene to be co-transformed into the organism. Alternatively, the additional gene(s) can be provided on multiple expression cassettes. Such an expression cassette is provided with a plurality of restriction sites and/or recombination sites for insertion of the RKD encoding polynucleotide to be under the transcriptional regulation of the ovule tissue-preferred promoter. The expression cassette may additionally contain selectable marker genes.
The expression cassette will include in the 5′-3′ direction of transcription, an ovule tissue-preferred promoter or an active variant or fragment thereof, an RKD encoding polynucleotide or active variant or fragment thereof, and a transcriptional and translational termination region (i.e., termination region) functional in the host cell (i.e., the plant). The regulatory regions (i.e., promoters, transcriptional regulatory regions and translational termination regions) and/or the RKD encoding polynucleotides may be native/analogous to the host cell or to each other. Alternatively, the regulatory regions and/or the RKD encoding polynucleotide or active fragments and variants thereof may be heterologous to the host cell or to each other.
As used herein, “heterologous” in reference to a sequence is a sequence that originates from a foreign species, or, if from the same species, is substantially modified from its native form in composition and/or genomic locus by deliberate human intervention. For example, a promoter operably linked to a heterologous polynucleotide is from a species different from the species from which the polynucleotide was derived, or, if from the same/analogous species, one or both are substantially modified from their original form and/or genomic locus, or the promoter is not the native promoter for the operably linked polynucleotide. As used herein, a chimeric gene comprises a coding sequence operably linked to a transcription initiation region that is heterologous to the coding sequence.
The termination region may be native with the transcriptional initiation region, may be native with the operably linked RKD encoding polynucleotide or with the ovule tissue-preferred promoter sequences, may be native with the plant host, or may be derived from another source (i.e., foreign or heterologous) to the promoter, the RKD encoding polynucleotide, the plant host or any combination thereof. Convenient termination regions are available from the Ti-plasmid of A. tumefaciens, such as the octopine synthase and nopaline synthase termination regions. See also, Guerineau, et al., (1991) Mol. Gen. Genet. 262:141-144; Proudfoot, (1991) Cell 64:671-674; Sanfacon, et al., (1991) Genes Dev. 5:141-149; Mogen, et al., (1990) Plant Cell 2:1261-1272; Munroe, et al., (1990) Gene 91:151-158; Ballas, et al., (1989) Nucleic Acids Res. 17:7891-7903 and Joshi, et al., (1987) Nucleic Acids Res. 15:9627-9639.
Thus, expression constructs are provided comprising an ovule tissue-preferred promoter operably linked to a heterologous polynucleotide encoding a RKD polypeptide, wherein the ovule tissue-preferred promoter is active in at least one non-gametophyte tissue in a plant ovule and the ovule tissue-preferred promoter is active in an unreduced ovule cell that is outside of the embryo sac of the plant. In still further embodiments, the polynucleotide encoding the RKD polypeptide in the expression construct encodes a polypeptide as set forth in SEQ ID NO: 12, 14, 16, 18 or 32 or it encodes a polypeptide having at least 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to the polypeptide set forth in SEQ ID NO: 12, 14, 16, 18 or 32, wherein said active variant retains RKD activity.
Moreover, the construct having the RDK encoding polynucleotide or active variant or fragment thereof can be operably linked to an ovule tissue-preferred promoter comprising the polynucleotide set forth in SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9 or 33 or a polynucleotide having at least 80%85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9 or 33, wherein said polynucleotide retains the ability to direct expression of an operably linked polynucleotide in an ovule tissue-preferred manner in at least one non-gametophyte tissue in a plant ovule.
In still further embodiments, the expression construct comprises (i) the polynucleotide set forth in SEQ ID NO: 1 or 3 operably linked to the polynucleotide sequence encoding the polypeptide set forth in SEQ ID NO: 14 or (ii) the polynucleotide having at least 95% sequence identity to the sequence set forth in SEQ ID NO: 1 or 3, wherein said polynucleotide retains the ability to direct expression of an operably linked polynucleotide in an ovule tissue-preferred manner in at least one non-gametophyte tissue in a plant ovule and said polynucleotide is operably linked to a polypeptide having at least 95% sequence identity to the polypeptide set forth in SEQ ID NO: 14, wherein said active variant retains RKD activity.
Where appropriate, the polynucleotides may be optimized for increased expression in the transformed plant. That is, the polynucleotides can be synthesized using plant-preferred codons for improved expression. See, for example, Campbell and Gowri, (1990) Plant Physiol. 92:1-11 for a discussion of host-preferred codon usage. Methods are available in the art for synthesizing plant-preferred genes. See, for example, U.S. Pat. Nos. 5,380,831 and 5,436,391 and Murray, et al., (1989) Nucleic Acids Res. 17:477-498, herein incorporated by reference.
Additional sequence modifications are known to enhance gene expression in a cellular host. These include elimination of sequences encoding spurious polyadenylation signals, exon-intron splice site signals, transposon-like repeats and other such well-characterized sequences that may be deleterious to gene expression. The G-C content of the sequence may be adjusted to levels average for a given cellular host, as calculated by reference to known genes expressed in the host cell. When possible, the sequence is modified to avoid predicted hairpin secondary mRNA structures.
The expression cassettes may additionally contain 5′ leader sequences. Such leader sequences can act to enhance translation. Translation leaders are known in the art and include: picornavirus leaders, for example, EMCV leader (Encephalomyocarditis 5′ noncoding region) (Elroy-Stein, et al., (1989) Proc. Natl. Acad. Sci. USA 86:6126-6130); potyvirus leaders, for example, TEV leader (Tobacco Etch Virus) (Gallie, et al., (1995) Gene 165(2):233-238), MDMV leader (Maize Dwarf Mosaic Virus) (Johnson, et al., (1986) Virology 154:9-20) and human immunoglobulin heavy-chain binding protein (BiP) (Macejak, et al., (1991) Nature 353:90-94); untranslated leader from the coat protein mRNA of alfalfa mosaic virus (AMV RNA 4) (Jobling, et al., (1987) Nature 325:622-625); tobacco mosaic virus leader (TMV) (Gallie, et al., (1989) in Molecular Biology of RNA, ed. Cech (Liss, N.Y.), pp. 237-256) and maize chlorotic mottle virus leader (MCMV) (Lommel, et al., (1991) Virology 81:382-385). See also, Della-Cioppa, et al., (1987) Plant Physiol. 84:965-968. Other methods known to enhance translation can also be utilized, for example, introns, and the like.
In preparing the expression cassette, the various DNA fragments may be manipulated, so as to provide for the DNA sequences in the proper orientation and, as appropriate, in the proper reading frame. Toward this end, adapters or linkers may be employed to join the DNA fragments or other manipulations may be involved to provide for convenient restriction sites, removal of superfluous DNA, removal of restriction sites, or the like. For this purpose, in vitro mutagenesis, primer repair, restriction, annealing, resubstitutions, e.g., transitions and transversions, may be involved.
The expression cassette can also comprise a selectable marker gene for the selection of transformed cells. Selectable marker genes are utilized for the selection of transformed cells or tissues. Marker genes include genes encoding antibiotic resistance, such as those encoding neomycin phosphotransferase II (NEO) and hygromycin phosphotransferase (HPT), as well as genes conferring resistance to herbicidal compounds, such as glufosinate ammonium, bromoxynil, imidazolinones and 2,4-dichlorophenoxyacetate (2,4-D). Additional selectable markers include phenotypic markers such as β-galactosidase and fluorescent proteins such as green fluorescent protein (GFP) (Su, et al., (2004) Biotechnol Bioeng 85:610-619 and Fetter, et al., (2004) Plant Cell 16:215-228), cyan florescent protein (CYP) (Bolte, et al., (2004) J. Cell Science 117:943-954 and Kato, et al., (2002) Plant Physiol 129:913-942) and yellow florescent protein (PhiYFP™ from Evrogen, see, Bolte, et al., (2004) J. Cell Science 117:943-954). For additional selectable markers, see generally, Yarranton, (1992) Curr. Opin. Biotech. 3:506-511; Christopherson, et al., (1992) Proc. Natl. Acad. Sci. USA 89:6314-6318; Yao, et al., (1992) Cell 71:63-72; Reznikoff, (1992) Mol. Microbiol. 6:2419-2422; Barkley, et al., (1980) in The Operon, pp. 177-220; Hu, et al., (1987) Cell 48:555-566; Brown, et al., (1987) Cell 49:603-612; Figge, et al., (1988) Cell 52:713-722; Deuschle, et al., (1989) Proc. Natl. Acad. Aci. USA 86:5400-5404; Fuerst, et al., (1989) Proc. Natl. Acad. Sci. USA 86:2549-2553; Deuschle, et al., (1990) Science 248:480-483; Gossen, (1993) Ph.D. Thesis, University of Heidelberg; Reines, et al., (1993) Proc. Natl. Acad. Sci. USA 90:1917-1921; Labow, et al., (1990) Mol. Cell. Biol. 10:3343-3356; Zambretti, et al., (1992) Proc. Natl. Acad. Sci. USA 89:3952-3956; Baim, et al., (1991) Proc. Natl. Acad. Sci. USA 88:5072-5076; Wyborski, et al., (1991) Nucleic Acids Res. 19:4647-4653; Hillenand-Wissman, (1989) Topics Mol. Struc. Biol. 10:143-162; Degenkolb, et al., (1991) Antimicrob. Agents Chemother. 35:1591-1595; Kleinschnidt, et al., (1988) Biochemistry 27:1094-1104; Bonin, (1993) Ph.D. Thesis, University of Heidelberg; Gossen, et al., (1992) Proc. Natl. Acad. Sci. USA 89:5547-5551; Oliva, et al., (1992) Antimicrob. Agents Chemother. 36:913-919; Hlavka, et al., (1985) Handbook of Experimental Pharmacology, Vol. 78 (Springer-Verlag, Berlin); Gill, et al., (1988) Nature 334:721-724. Such disclosures are herein incorporated by reference. The above list of selectable marker genes is not meant to be limiting. Any selectable marker gene can be used.
It is further recognized that various expression constructs other than the RKD expression construct are described herein. For example, expression constructs having sequences encoding marker sequences, cytotoxic polypeptides and embryo-inducing polypeptides are also described herein. One of skill will understand how to apply the language discussed above, to any expression construct.
V. Sequences Encoding Embryo-Inducing Polypeptides
Methods and compositions are provided to increase the activity/level of an RKD polypeptide in an unreduced ovule plant cell that is outside of the embryo sac. In specific embodiments, such modulation of activity/level of the RKD polypeptide promotes an egg cell-like state in an unreduced ovule plant cell that is outside of the embryo sac. As discussed above, such methods and compositions employ an expression construct comprising an RKD encoding polynucleotide operably linked to an ovule tissue-preferred promoter. Such methods and compositions can further be employed in combination with other sequences which encode embryo-inducing polypeptides.
As used herein, an “embryo-inducing polypeptide” comprises any sequence which when expressed in combination with the RKD encoding polypeptide operably linked to an ovule tissue-preferred promoter further promotes the development of the egg cell-like state, including further promoting an egg cell-like transcription state, promoting the development of egg cell-like structures, promoting adventitious embryony and/or promoting partial adventitious embryony. Such embryo-inducing polyepetides can promote growth through triggering developmental programs.
Such embryo-inducing sequence include, but are not limited to, Somatic Embryogenesis receptor-like kinase (SERK) (Schmidt, et al., (1997) Development 124:2049-62), Wushel (WUS) (Zuo, et al., (2001) The Plant Journal 30:349-359), the family of LEC polypeptides including, Leafy Cotyledon1 (LEC1) (Lotan, et al., (1998) Cell 93:1195-1205) and Leafy Cotyledon2 (LEC2) (Stone, et al., (2001) PNAS 98:11806-11811), Baby Boom (BBM) (Boutilier, et al., (2002) Plant Cell 14:1737-1749) and agamous-like 15 (Harding, et al., (2003) Plant Physiol. 133:653-663), EMBRYOMAKER (EMK) (Tsuwamoto, et al., (2010) Plant Molecular Biology 73:481-492).
In specific embodiments, the embryo-inducing sequence is involved in organ development, initiation and/or development of the apical meristem. Such sequences include, for example, Wuschel (WUS) or active variants and fragments thereof. See U.S. Pat. Nos. 7,348,468 and 7,256,322 and US Patent Application Publication Number 2007/0271628; Laux, et al., (1996) Development 122:87-96 and Mayer, et al., (1998) Cell 95:805-815, each of which are herein incorporated by reference. Modulation of WUS is expected to modulate plant and/or plant tissue phenotype including cell growth stimulation, organogenesis, and somatic embryogenesis. WUS may also be used to improve transformation via somatic embryogenesis. Expression of Arabidopsis WUS can induce stem cells in vegetative tissues, which can differentiate into somatic embryos (Zuo, et al., (2002) Plant J 30:349-359).
In yet another embodiment, a MYB118 gene (see, U.S. Pat. No. 7,148,402), MYB115 gene (see, Wang, et al., (2008) Cell Research 224-235), BABYBOOM gene (BBM; see Boutilier, et al., (2002) Plant Cell 14:1737-1749), LEC and/or CLAVATA gene (see, for example, U.S. Pat. No. 7,179,963) is co-expressed with at least one expression cassette comprising at least one RKD family member polypeptide.
In specific embodiments, the embryo-inducing sequence encodes a Leafy Cotyledon polypeptide (LEC) or an active variant or fragment thereof. The LEC family of transcription factors is involved in embryo maturation and functions in early developmental stages to maintain embryonic cell fate and have been shown to promote formation of embryo-like structures. See, for example, Lotan, et al., (1998) Cell 93:1195-1205; Braybrook, et al., (2008) Trends in Plant Science 13:624-630; Stone, (2001) PNAS 98:11806-11811; Gazzarrini, et al., (2004) Dev Cell 7:373-385; Gaj, et al., (2005) Planta 222:977-988; Wang, et al., (2007) Planta 226:773-783.
BABY BOOM (BBM or BNM3) or active variant and fragments thereof show similarity to the AP2/ERF family of transcription factors and is expressed preferentially in developing embryos and seeds. Ectopic expression of BBM in plants leads to the spontaneous formation of somatic embryos and cotyledon-like structures on seedlings. Ectopic BBM expression induced additional pleiotropic phenotypes, including neoplastic growth, hormone-free regeneration of explants and alterations in leaf and flower morphology. BBM plays a role in promoting cell proliferation and morphogenesis during embryogenesis. See, Boutilier, et al., (2002) Plant Cell 14:1737-1749 and EP 1057891 (A1), both of which are herein incorporated by reference.
Other embryo-inducing polypeptides include members of the ARIADNE-subclass of RING-finger proteins. See, for example, Jackson, et al., (2000) Trends Cell Biol. 10:429-439 and Mladek, et al., (2003) Plant Physiol. 131:27-40, both of which are herein incorporated by reference. The ARIADNE proteins belong to a family of E3 ligases present in yeast, plants and animals and thought to be involved in the control of ubiquitin-dependent protein degradation (reviewed in Vierstra, (2003) Trends Plant Sci. 8:135-142). One member of the ARIADNE gene family is ARIADNE7 (ARI7). See, for example, Schallan, et al., (2010) The Plant Journal 62:773-784, herein incorporated by reference.
Biologically active variants of an embryo-inducing polypeptide (and the polynucleotide encoding the same) will have at least about 70%. 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more sequence identity to any embryo-inducing polypeptide, including but not limited to, the polypeptide of any one of SERK; Wushel (WUS); the family of LEC polypeptides; Baby Boom (BBM) and agamous-like 15, as determined by sequence alignment programs and parameters described elsewhere herein.
Thus, the RKD encoding polynucleotides operably linked to the ovule tissue-preferred promoters can further be stacked with any combination of polynucleotide sequences of interest, particularly a sequence encoding an embryo-inducing polypeptide. Such stacking can occur within the same expression cassette or the two different sequences can be introduced into the plant separately. The desired stacked combinations can be created by any method including, but not limited to, cross-breeding plants by any conventional or TopCross methodology, or genetic transformation. If the sequences are stacked by genetically transforming the plants, the polynucleotide sequences of interest can be combined at any time and in any order. For example, a transgenic plant comprising one or more desired traits can be used as the target to introduce further traits by subsequent transformation. The traits can be introduced simultaneously in a co-transformation protocol with the polynucleotides of interest provided by any combination of transformation cassettes. For example, if two sequences will be introduced, the two sequences can be contained in separate transformation cassettes (trans) or contained on the same transformation cassette (cis). Expression of the sequences can be driven by the same promoter or by different promoters. It is further recognized that polynucleotide sequences can be stacked at a desired genomic location using a site-specific recombination system. See, for example, WO 1999/25821, WO 1999/25854, WO 1999/25840, WO 1999/25855 and WO 1999/25853, all of which are herein incorporated by reference.
One of skill will recognize that the sequences encoding the embryo-inducing polypeptides can be placed into an expression cassette. Expression cassettes are discussed elsewhere herein. Any promoter of interest can be operably linked to the sequence encoding the embryo-inducing polypeptides, including for example, constitutive promoters, tissue-preferred promoters, tissue-specific promoters, ovule tissue-preferred promoters, an ovule tissue-preferred promoter that is active in at least one non-gametophyte tissue in a plant ovule, seed-preferred, embryo-preferred and/or endosperm preferred promoters. Many such promoters have been described elsewhere herein.
Non-limiting examples of constitutive promoters include, for example, the core promoter of the Rsyn7 promoter and other constitutive promoters disclosed in WO 1999/43838 and U.S. Pat. No. 6,072,050; the core CaMV 35S promoter (Odell, et al., (1985) Nature 313:810-812); rice actin (McElroy, et al., (1990) Plant Cell 2:163-171); ubiquitin (Christensen, et al., (1989) Plant Mol. Biol. 12:619-632 and Christensen, et al., (1992) Plant Mol. Biol. 18:675-689); pEMU (Last, et al., (1991) Theor. Appl. Genet. 81:581-588); MAS (Velten, et al., (1984) EMBO J. 3:2723-2730); ALS promoter (U.S. Pat. No. 5,659,026), and the like. Other constitutive promoters include, for example, U.S. Pat. Nos. 5,608,149; 5,608,144; 5,604,121; 5,569,597; 5,466,785; 5,399,680; 5,268,463; 5,608,142 and 6,177,611.
“Seed-preferred” promoters include both “seed-specific” promoters (those promoters active during seed development such as promoters of seed storage proteins) as well as “seed-germinating” promoters (those promoters active during seed germination). See, Thompson, et al., (1989) BioEssays 10:108, herein incorporated by reference. Such seed-preferred promoters include, but are not limited to, Cim1 (cytokinin-induced message); cZ19B1 (maize 19 kDa zein); milps (myo-inositol-1-phosphate synthase) (see, WO 2000/11177 and U.S. Pat. No. 6,225,529, herein incorporated by reference). HV-NUC1 is a barley nucellus-specific promoter. Gamma-zein is an endosperm-specific promoter. Globulin 1 (Glb-1) is a representative embryo-specific promoter. For dicots, seed-specific promoters include, but are not limited to, bean β-phaseolin, napin, β-conglycinin, soybean lectin, cruciferin and the like. For monocots, seed-specific promoters include, but are not limited to, maize 15 kDa zein, 22 kDa zein, 27 kDa zein, gamma-zein, waxy, shrunken 1, shrunken 2, Globulin 1, etc. See also, WO 2000/12733, where seed-preferred promoters from end1 and end2 genes are disclosed, herein incorporated by reference. Other specific promoters that could be used to express the embryo-inducing polypeptide include but are not limited to: AT-SVL3 PRO; AT-EXT PRO; AT-GILT1 PRO; AT-PPM1 PRO; AT-TT2 PRO; AT-BAN1 PRO, AT-DD1 PRO.
VI. Sequence Encoding Cytotoxic Polypeptides
As discussed above, methods and compositions are provided to increase the activity/level of an RKD polypeptide in an unreduced ovule plant cell that is outside of the embryo sac. In specific embodiments, such modulation of activity/level of the RKD polypeptide promotes an egg cell-like state in an unreduced ovule plant cell that is outside of the embryo sac. Development of such a state (i.e., a transcriptional egg cell-like state or the development of embryo-like structures in tissues and substructures outside of the egg cell, including the formation of such structures in any tissues and substructures suitable for adventitious embryony) may be improved by further employing cytotoxic polypeptides which are expressed in a manner that allows for the targeted cell death or ablation of specific cell types of the embryo sac. In specific embodiments, at least the egg cell is ablated.
In specific embodiments, the egg cell in the plant ovule is specifically ablated and thereby the formation of the zygotic embryo is prevented. Since only the egg cell is ablated, fertilization of the central cell should be possible along with some degree of endosperm development. Prevention of the zygotic embryo allows for the synthetic apospory approach to self-reproducing hybrids, or clonally reproducing plants. That is, the zygotic embryo is not formed, but an adventitious embryo is formed from non-reduced cells in the ovule through the expression of the RDK polypeptide as disclosed herein.
Thus, such methods which ablate the egg cell can be employed in combination with an expression construct comprising an ovule tissue-preferred promoter operably linked to a heterologous polynucleotide encoding a RKD polypeptide, wherein the ovule tissue-preferred promoter is active in at least one non-gametophyte tissue in a plant ovule and the ovule tissue-preferred promoter is active in an unreduced ovule cell that is outside of the embryo sac of the plant.
Various cytotoxic polypeptides can be used for the targeted cell death or ablation of specific cell types of the embryo sac. In addition to the cytotoxin sequences outlined below, other possible cytotoxins include: alpha amylases, other nucleases; any method of gene silencing targeting genes that are required for egg cell development and/or expression of any protein or nucleic acid know to lead to cell death. Additional methods and compositions to ablate the egg cell, include, for example, an embryo-lethal mutation that is crossed into the plant can also be employed.
Such cytotoxic polypeptides include Barnase (a portmanteau of “BActerial” “RiboNucleASE”) which is a bacterial protein that consists of 110 amino acids and has ribonuclease activity. A non-limiting example of the barnase polypeptide is set forth in SEQ ID NO: 23. Note, INT refers to the addition of ST-LS1 INTRON2. Active fragments and variants thereof can further be employed, wherein said active fragments and variants retain cytotoxic activity in the cells in which they are expressed. Barnase is synthesized and secreted by the bacterium Bacillus amyloliquefaciens, but is lethal to the cell when expressed without its inhibitor barstar. The inhibitor binds to and occludes the ribonuclease active site, preventing barnase from damaging the cell's RNA after it has been synthesized, but before it has been secreted. See, for example, Buckle, et al., (1994) Biochemistry 33(30):8878-8889; Serrano, et al., (1992) J. Mol. Biol. 224(3):783-804; Serrano, et al., (1992). J. Mol. Biol. 224(3):805-818; Matouschek, et al., (1992) J. Mol. Biol. 224(3):819-835; Mossakowska, et al., (1989) Biochemistry 28(9):3843-3850; Gils, et al., (2008) Plant Biotechnology Journal 6:226-235 and Kempe, et al., (2009) Plant Biotechnology Journal 7:283-297.
Additional cytotoxins that can be employed include, but are not limited to, a Dam Methylase as set forth in SEQ ID NO: 24 or an active variants or fragments thereof, or the Dam Methylase Intein Split: DMETH N-term (SEQ ID NO: 25); INTE-N (SEQ ID NO: 26); INTE-C (SEQ ID NO: 27); DMETH C-TERM (SEQ ID NO: 28) or active variants or fragments thereof; or the ADP Ribosylase polypeptide (SEQ ID NO: 29) or active variants or fragments thereof.
Cell ablation to manipulate fertilization and/or seed development could include, for example, use of one or more cell-type-specific promoters disclosed herein. Thus, one of skill will recognize that the sequences encoding the cytotoxic polypeptides can be placed into an expression cassette. Expression cassettes are discussed elsewhere herein. Any promoter of interest can be operably linked to the sequence encoding the cytotoxic polypeptide, so long as the promoter directs expression of the cytotoxic polypeptide in cell type that one desires to ablate. Individual promoters would be particularly useful for cell ablation to prevent pollen tube attraction for fertilization (synergid ablation, DD31 or DD2); prevent sexual embryo formation (egg cell ablation, DD45) and/or prevent endosperm formation (central cell ablation, DD65). Such promoters include, for example, an embryo sac-preferred promoter or an embryo sac-specific promoter, including an egg cell-preferred promoter. Such egg-preferred promoters will not be active in the central cell or the endosperm and thereby these tissues are preserved when the egg cell-preferred promoter is operably linked to the sequence encoding the cytotoxic polypeptide. Such egg cell-preferred promoters include the Arabidopsis promoter (AT-DD45 PRO; Arabidopsis thaliana downregulated in dif1 (determinant infertile1; SEQ ID NO: 10; At2g21740 promoter) and active variants and fragments thereof. Analysis shows that this promoter is specific to the egg cell and zygote/early embryo and is not expressed in any other cell types. When the AT-DD45 PRO is employed to express a cytotoxic polypeptide the egg cells in plant ovules will be specifically ablated. See, Steffen, et al., (2007) Plant J 51(2):281-292. Using the DD45 promoter to express a toxin (e.g., BARNASE) would lead to egg cell ablation, and prevent formation of the zygotic embryo. Since only the egg cell would be ablated, fertilization of the central cell should be possible along with some degree of endosperm development. Thus, such a construct when combined with the various methods disclosed herein can be used in the development of synthetic apospory.
Additional embryo sac-preferred promoters that can be used to express cytotoxic polypeptide include the antipodal cell-preferred promoter AT-DD1 PRO (SEQ ID NO: 41; downregulated with dif1 (determinant infertile1)1; At1g36340); a synergid cell-preferred promoter (AT-DD31 PRO; SEQ ID NO: 41; downregulated with dif1 (determinant infertile1)1 31; At1g47470); and/or a central cell-preferred promoter (ATDD65PRO; SEQ ID NO: 43); downregulated with dif1 (determinant infertile1)1 65; At3g10890); Fem 2 (SEQ ID NO: 30; central-cell preferred/polar nuclei preferred) and active variant and fragments thereof. See also, U.S. Provisional Application Ser. No. ______, entitled Ovule Specific Promoters and Methods of Their Use, filed concurrently herewith and herein incorporated by reference in its entirety and Steffen, et al., (2007) The Plant Journal 51:281-292, herein incorporated by reference.
VII. Variants and Fragments of Promoters
As discussed herein various promoters can be employed in the methods and compositions provided herein, including: promoters to express sequences encoding the embryo-inducing polypeptides and the sequences encoding the cytotoxic polypeptides. Fragments and variants of these promoter polynucleotides can be employed. Fragments of a promoter polynucleotide may retain biological activity and hence retain transcriptional regulatory activity in the desired tissue as the unmodified form. Thus, fragments of a promoter nucleotide sequence may range from at least about 20 nucleotides, about 50 nucleotides, about 100 nucleotides and up to the full-length promoter sequence. Thus, a fragment of a promoter polynucleotide may encode a biologically active portion of a promoter. A biologically active portion of a promoter polynucleotide can be prepared by isolating a portion of one of the promoter polynucleotides and assessing the activity of the portion of the promoter. Polynucleotides that are fragments of the polynucleotide comprise at least 16, 20, 50, 75, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 800, 900, 1,000, 1,100, 1,200, 1,300, 1,400, 1,500, 1,600, 1,700, 1,800, 1,900, 2000 nucleotides or up to the number of nucleotides present in a full-length promoter polynucleotide disclosed herein.
For a promoter polynucleotide, a variant comprises a deletion and/or addition of one or more nucleotides at one or more internal sites within the native polynucleotide and/or a substitution of one or more nucleotides at one or more sites in the native polynucleotide. Generally, variants of a particular promoter polynucleotide of the disclosure will have at least about 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more sequence identity to that particular polynucleotide as determined by sequence alignment programs and parameters described elsewhere herein.
Methods are described elsewhere herein for determining if a promoter sequence retains the ability to regulate transcription in the desired temporal and spatial pattern.
It is recognized that to increase transcription levels, enhancers may be utilized in combination with the promoter disclosed herein. Enhancers are nucleotide sequences that act to increase the expression of a promoter region. Enhancers are known in the art and include the SV40 enhancer region, the 35S enhancer element and the like. Some enhancers are also known to alter normal promoter expression patterns, for example, by causing a promoter to be expressed constitutively when without the enhancer, the same promoter is expressed only in one specific tissue or a few specific tissues.
Modifications of the promoters disclosed herein can provide for a range of expression of the heterologous nucleotide sequence. Thus, they may be modified to be weak promoters or strong promoters. Generally, a “weak promoter” means a promoter that drives expression of a coding sequence at a low level. A “low level” of expression is intended to mean expression at levels of about 1/10,000 transcripts to about 1/100,000 transcripts to about 1/500,000 transcripts. Conversely, a strong promoter drives expression of a coding sequence at a high level or at about 1/10 transcripts to about 1/100 transcripts to about 1/1,000 transcripts.
IIX. Plants and Methods of Making
The methods disclosed herein involve introducing a polypeptide or polynucleotide into a plant. “Introducing” is intended to mean presenting to the plant the polynucleotide or polypeptide in such a manner that the sequence gains access to the interior of a cell of the plant. The methods disclosed herein do not depend on a particular method for introducing a sequence into a plant, only that the polynucleotide or polypeptides gains access to the interior of at least one cell of the plant. Methods for introducing polynucleotide or polypeptides into plants are known in the art including, but not limited to, stable transformation methods, transient transformation methods and virus-mediated methods.
“Stable transformation” is intended to mean that the nucleotide construct introduced into a plant integrates into the genome of the plant and is capable of being inherited by the progeny thereof. “Transient transformation” is intended to mean that a polynucleotide is introduced into the plant and does not integrate into the genome of the plant or a polypeptide is introduced into a plant.
Transformation protocols as well as protocols for introducing polypeptides or polynucleotide sequences into plants may vary depending on the type of plant or plant cell, i.e., monocot or dicot, targeted for transformation. Suitable methods of introducing polypeptides and polynucleotides into plant cells include microinjection (Crossway, et al., (1986) Biotechniques 4:320-334), electroporation (Riggs, et al., (1986) Proc. Natl. Acad. Sci. USA 83:5602-5606), Agrobacterium -mediated transformation (U.S. Pat. No. 5,563,055 and U.S. Pat. No. 5,981,840), direct gene transfer (Paszkowski, et al., (1984) EMBO J. 3:2717-2722) and ballistic particle acceleration (see, for example, U.S. Pat. No. 4,945,050; U.S. Pat. No. 5,879,918; U.S. Pat. Nos. 5,886,244 and 5,932,782; Tomes, et al., (1995) in Plant Cell, Tissue, and Organ Culture: Fundamental Methods, ed. Gamborg and Phillips (Springer-Verlag, Berlin); McCabe, et al., (1988) Biotechnology 6:923-926) and Led transformation (WO 2000/28058). Also see, Weissinger, et al., (1988) Ann. Rev. Genet. 22:421-477; Sanford, et al., (1987) Particulate Science and Technology 5:27-37 (onion); Christou, et al., (1988) Plant Physiol. 87:671-674 (soybean); McCabe, et al., (1988) Bio/Technology 6:923-926 (soybean); Finer and McMullen, (1991) In Vitro Cell Dev. Biol. 27P:175-182 (soybean); Singh, et al., (1998) Theor. Appl. Genet. 96:319-324 (soybean); Datta, et al., (1990) Biotechnology 8:736-740 (rice); Klein, et al., (1988) Proc. Natl. Acad. Sci. USA 85:4305-4309 (maize); Klein, et al., (1988) Biotechnology 6:559-563 (maize); U.S. Pat. Nos. 5,240,855; 5,322,783 and 5,324,646; Klein, et al., (1988) Plant Physiol. 91:440-444 (maize); Fromm, et al., (1990) Biotechnology 8:833-839 (maize); Hooykaas-Van Slogteren, et al., (1984) Nature (London) 311:763-764; U.S. Pat. No. 5,736,369 (cereals); Bytebier, et al., (1987) Proc. Natl. Acad. Sci. USA 84:5345-5349 (Liliaceae); De Wet, et al., (1985) in The Experimental Manipulation of Ovule Tissues, ed. Chapman, et al., (Longman, N.Y.), pp. 197-209 (pollen); Kaeppler, et al., (1990) Plant Cell Reports 9:415-418 and Kaeppler, et al., (1992) Theor. Appl. Genet. 84:560-566 (whisker-mediated transformation); D'Halluin, et al., (1992) Plant Cell 4:1495-1505 (electroporation); Li, et al., (1993) Plant Cell Reports 12:250-255 and Christou and Ford, (1995) Annals of Botany 75:407-413 (rice); Osjoda, et al., (1996) Nature Biotechnology 14:745-750 (maize via Agrobacterium tumefaciens ), all of which are herein incorporated by reference.
In specific embodiments, the various sequences employed in the methods and compositions disclosed herein (e.g., the RKD polypeptides, the embryo-inducing sequences, the cytotoxic polypeptides, etc.) can be provided to a plant using a variety of transient transformation methods. Such transient transformation methods include, but are not limited to, the introduction of the various sequences employed in the methods and compositions disclosed herein (e.g., the RKD polypeptides, the embryo-inducing sequences, the cytotoxic polypeptides, etc. or variants and fragments thereof) directly into the plant or the introduction of the transcript into the plant. Such methods include, for example, microinjection or particle bombardment. See, for example, Crossway, et al., (1986) Mol Gen. Genet. 202:179-185; Nomura, et al., (1986) Plant Sci. 44:53-58; Hepler, et al., (1994) Proc. Natl. Acad. Sci. 91: 2176-2180 and Hush, et al., (1994) The Journal of Cell Science 107:775-784, all of which are herein incorporated by reference.
Alternatively, the various sequences employed in the methods and compositions disclosed herein (e.g., the RKD polypeptides, the embryo-inducing sequences, the cytotoxic polypeptides, etc.) can be transiently transformed into the plant using techniques known in the art. Such techniques include viral vector system and the precipitation of the polynucleotide in a manner that precludes subsequent release of the DNA. Thus, the transcription from the particle-bound DNA can occur, but the frequency with which it is released to become integrated into the genome is greatly reduced. Such methods include the use particles coated with polyethyleneimine (PEI; Sigma #P3143).
In other embodiments, the polynucleotide of the disclosure may be introduced into plants by contacting plants with a virus or viral nucleic acids. Generally, such methods involve incorporating a nucleotide construct of the disclosure within a viral DNA or RNA molecule. It is recognized that the various sequences employed in the methods and compositions disclosed herein (e.g., the RKD polypeptides, the embryo-inducing sequences, the cytotoxic polypeptides, etc.) may be initially synthesized as part of a viral polyprotein, which later may be processed by proteolysis in vivo or in vitro to produce the desired recombinant protein. Further, it is recognized that promoters disclosed herein also encompass promoters utilized for transcription by viral RNA polymerases. Methods for introducing polynucleotides into plants and expressing a protein encoded therein, involving viral DNA or RNA molecules, are known in the art. See, for example, U.S. Pat. Nos. 5,889,191, 5,889,190, 5,866,785, 5,589,367, 5,316,931 and Porta, et al., (1996) Molecular Biotechnology 5:209-221, herein incorporated by reference.
Methods are known in the art for the targeted insertion of a polynucleotide at a specific location in the plant genome. In one embodiment, the insertion of the polynucleotide at a desired genomic location is achieved using a site-specific recombination system. See, for example, WO 1999/25821, WO 1999/25854, WO 1999/25840, WO 1999/25855 and WO 1999/25853, all of which are herein incorporated by reference. Briefly, the polynucleotide of the disclosure can be contained in a transfer cassette flanked by two non-recombinogenic recombination sites. The transfer cassette is introduced into a plant having stably incorporated into its genome a target site which is flanked by two non-recombinogenic recombination sites that correspond to the sites of the transfer cassette. An appropriate recombinase is provided and the transfer cassette is integrated at the target site. The polynucleotide of interest is thereby integrated at a specific chromosomal position in the plant genome.
Additional methods for targeted mutagenesis in vivo are known. For example, a DNA sequence having the desired sequence alteration can be flanked by sequences homologous to the genomic target. One can then select or screen for a successful homologous recombination event. See, U.S. Pat. No. 5,527,695. Generally, such a vector construct is designed having two regions of homology to the genomic target which flank a polynucleotide having the desired sequence. Introduction of the vector into a plant cell will allow homologous recombination to occur and to produce an exchange of sequences between the homologous regions at the target site.
Such methods of homologous recombination can further be combined with agents that induce site-specific genomic double-stranded breaks in plant cells. Such double strand break agents can be engineered to produce the break at a targeted site and thereby enhance the homologous recombination events. See, for example, Puchta, et al., (1996) Proc Natl Acad Sci USA 93:5055-5060; US Patent Application Publication Number 2005/0172365A1; US Patent Application Publication Number 2006/0282914, WO 2005/028942; WO 2004/067736 published Aug. 12, 2004; U.S. Pat. No. 5,792,632; U.S. Pat. No. 6,610,545; Chevalier, et al., (2002) Mol Cell 10:895-905; Chevalier, et al., (2001) Nucleic Acids Res 29:3757-3774; Seligman, et al., (2002) Nucleic Acids Res 30:3870-3879; US Patent Application Publication Number 2009/0133152 and WO 2005/049842, each of which is herein incorporated by reference in their entirety.
The cells that have been transformed may be grown into plants in accordance with conventional ways. See, for example, McCormick, et al., (1986) Plant Cell Reports 5:81-84. These plants may then be grown, and either pollinated with the same transformed strain or different strains and the resulting progeny having constitutive expression of the desired phenotypic characteristic identified. Two or more generations may be grown to ensure that expression of the desired phenotypic characteristic is stably maintained and inherited and then seeds harvested to ensure expression of the desired phenotypic characteristic has been achieved. In this manner, the present disclosure provides transformed seed (also referred to as “transgenic seed”) having a polynucleotide of the disclosure, for example, an expression cassette of the disclosure, stably incorporated into their genome.
As used herein, the term plant includes plant cells, plant protoplasts, plant cell tissue cultures from which plants can be regenerated, plant calli, plant clumps and plant cells that are intact in plants or parts of plants such as embryos, pollen, ovules, seeds, leaves, flowers, branches, fruit, kernels, ears, cobs, husks, stalks, roots, root tips, anthers and the like. Grain is intended to mean the mature seed produced by commercial growers for purposes other than growing or reproducing the species. Progeny, variants, and mutants of the regenerated plants are also included within the scope of the disclosure, provided that these parts comprise the introduced polynucleotides.
The methods and compositions disclosed herein may be used for transformation of any plant species, including, but not limited to, monocots and dicots. Examples of plant species of interest include, but are not limited to, corn ( Zea mays ), Brassica sp. (e.g., B. napus, B. rapa, B. juncea ), particularly those Brassica species useful as sources of seed oil, alfalfa ( Medicago sativa ), rice ( Oryza sativa ), rye ( Secale cereale ), sorghum ( Sorghum bicolor, Sorghum vulgare ), millet (e.g., pearl millet ( Pennisetum glaucum ), proso millet ( Panicum miliaceum ), foxtail millet ( Setaria italica ), finger millet ( Eleusine coracana )), sunflower ( Helianthus annuus ), safflower ( Carthamus tinctorius ), wheat ( Triticum aestivum ), soybean ( Glycine max ), tobacco ( Nicotiana tabacum ), potato ( Solanum tuberosum ), peanuts ( Arachis hypogaea ), cotton ( Gossypium barbadense, Gossypium hirsutum ), sweet potato ( Ipomoea batatus ), cassava ( Manihot esculenta ), coffee ( Coffea spp.), coconut ( Cocos nucifera ), pineapple ( Ananas comosus ), citrus trees ( Citrus spp.), cocoa ( Theobroma cacao ), tea ( Camellia sinensis ), banana ( Musa spp.), avocado ( Persea americana ), fig ( Ficus casica ), guava ( Psidium guajava ), mango ( Mangifera indica ), olive ( Olea europaea ), papaya ( Carica papaya ), cashew ( Anacardium occidentale ), macadamia ( Macadamia integrifolia ), almond ( Prunus amygdalus ), sugar beets ( Beta vulgaris ), sugarcane ( Saccharum spp.), oats, barley, vegetables, ornamentals and conifers.
Vegetables include tomatoes ( Lycopersicon esculentum ), lettuce (e.g., Lactuca sativa ), green beans ( Phaseolus vulgaris ), lima beans ( Phaseolus limensis ), peas ( Lathyrus spp.), and members of the genus Cucumis such as cucumber ( C. sativus ), cantaloupe ( C. cantalupensis ) and musk melon ( C. melo ). Ornamentals include azalea ( Rhododendron spp.), hydrangea ( Macrophylla hydrangea ), hibiscus ( Hibiscus rosasanensis ), roses ( Rosa spp.), tulips ( Tulipa spp.), daffodils ( Narcissus spp.), petunias ( Petunia hybrida ), carnation ( Dianthus caryophyllus ), poinsettia ( Euphorbia pulcherrima ) and chrysanthemum.
Conifers that may be employed in practicing the present disclosure include, for example, pines such as loblolly pine ( Pinus taeda ), slash pine ( Pinus elliotii ), ponderosa pine ( Pinus ponderosa ), lodgepole pine ( Pinus contorta ) and Monterey pine ( Pinus radiata ); Douglas-fir ( Pseudotsuga menziesii ); Western hemlock ( Tsuga canadensis ); Sitka spruce ( Picea glauca ); redwood ( Sequoia sempervirens ); true firs such as silver fir ( Abies amabilis ) and balsam fir ( Abies balsamea ) and cedars such as Western red cedar ( Thuja plicata ) and Alaska yellow-cedar ( Chamaecyparis nootkatensis ). In specific embodiments, plants of the present disclosure are crop plants (for example, corn, alfalfa, sunflower, Brassica sp., soybean, cotton, safflower, peanut, sorghum, wheat, millet, tobacco, etc.). In other embodiments, corn and soybean plants are optimal, and in yet other embodiments corn plants are optimal.
Other plants of interest include grain plants that provide seeds of interest, oil-seed plants and leguminous plants. Seeds of interest include grain seeds, such as corn, wheat, barley, rice, sorghum, rye, etc. Oil-seed plants include cotton, soybean, safflower, sunflower, Brassica sp., maize, alfalfa, palm, coconut, etc. Leguminous plants include beans and peas. Beans include guar, locust bean, fenugreek, soybean, garden beans, cowpea, mungbean, lima bean, fava bean, lentils, chickpea, etc
IX. Various Methods of Use
Methods for promoting an egg cell-like state in an unreduced ovule plant cell that is outside the embryo sac are provided. Such methods comprise expressing an expression construct comprising an ovule tissue-preferred promoter operably linked to a heterologous polynucleotide encoding a RKD polypeptide, wherein the ovule tissue-preferred promoter is active in at least one non-gametophyte tissue in a plant ovule and the ovule tissue-preferred promoter is active in an unreduced ovule cell that is outside of the embryo sac of the plant. Such methods promote an egg cell-like state in at least one unreduced ovule cell of the plant outside of the embryo sac. In specific embodiments, the methods disclosed herein provide for the “egg cell-like state” to progress into the creation of adventitious embryony or partial embryony.
The ability to stimulate organogenesis and/or somatic embryogenesis may be used to generate an apomictic plant. Apomixis has economic potential because it can cause any genotype, regardless of how heterozygous, to breed true. It is a reproductive process that bypasses female meiosis and syngamy to produce embryos genetically identical to the maternal parent. With apomictic reproduction, progeny of a specially adaptive or hybrid genotypes would maintain their genetic fidelity throughout repeated life cycles. In addition to fixing hybrid vigor, apomixis can make possible commercial hybrid production in crops where efficient male sterility or fertility restoration systems for producing hybrids are not available. Apomixis can make hybrid development more efficient. It also simplifies hybrid production and increases genetic diversity in plant species with good male sterility. Furthermore, apomixis may be advantageous under stress (drought, cold, high-salinity, etc.) conditions where pollination may be compromised.
In specific embodiments, the encoded RKD polypeptide employed in the methods disclosed herein comprises a polypeptide as set forth in SEQ ID NO: 12, 14, 16, 18 or 32 or an active variant or fragment thereof. In addition, the ovule tissue-preferred promoter can comprise the polynucleotide set forth in SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9 or 33 or an active variant or fragment thereof. In still further embodiments, the expression construct comprises the polynucleotide set forth in SEQ ID NO: 1 or 3 or an active variant thereof operably linked to the polynucleotide sequence encoding the polypeptide set forth in SEQ ID NO: 14 or an active variant or fragment thereof.
Additional sequences can be used in the methods to promote the formation of an egg-like state. For example, expression of a RDK polypeptide from an ovule tissue-preferred promoter can be combined with the expression of an embryo-inducing polypeptide. Such embryo-inducing polypeptides are discussed elsewhere herein and comprises a BBM, WUS, LEC, MYB115, MYB118 and/or ARI7 polypeptide or an active variant thereof. The sequences encoding such embryo inducing polypeptides can be operably linked to any promoter including for example, an ovule tissue-preferred promoter.
In still further embodiments, the RKD polypeptide is expressed in combination with a second polynucleotide which when expressed will ablate at least one cell within the embryo sac. In non-limiting examples, the second expression construct comprises an embryo-sac specific promoter operably linked to a polynucleotide which when expressed will ablate at least one cell within the embryo sac. The embryo sac-preferred promoter can be an antipodal cell-preferred promoter, a synergid cell-preferred promoter, an egg cell-preferred promoter or a central cell-preferred promoter. While in other embodiments, the embryo sac-preferred promoter is an egg cell-preferred promoter and comprises the polynucleotide set forth in SEQ ID NO: 10 or an active variant of fragment thereof.
Various methods and compositions that can be used to detect an egg-cell like state, an egg cell-like transcriptional state, development of egg cell-like structures, adventitious embryony and partial adventitious embryony are discussed elsewhere herein. In this manner, an egg cell-like state can be assayed for in tissues of the plant ovule including any tissues and substructures suitable for adventitious embryony.
Further provided are methods for modulating the concentration and/or activity of the RKD polypeptide or active variant thereof in at least one non-gametophyte tissue in a plant ovule. In other embodiments, the modulation of the concentration and/or activity of the RKD polypeptide occurs in an unreduced ovule cell that is outside of the embryo sac of the plant. In general, concentration and/or activity is increased by at least 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% relative to a native control plant, plant part, or cell. Modulation in the present disclosure may occur during and/or subsequent to growth of the plant to the desired stage of development.
In specific embodiments, the methods of modulation (i.e., increasing) the concentration and/or activity of the RKD polypeptide or an active variant or fragment thereof comprises introducing into the plant or plant cell a polynucleotide encoding the RKD polypeptide employed comprises a polypeptide as set forth in SEQ ID NO: 12, 14, 16, 18 or 32 or an active variant or fragment thereof. In other embodiments, the sequence encoding the RKD polypeptide is operably linked to an ovule tissue-preferred promoter, which can comprise the polynucleotide set forth in SEQ ID NO: 1, 2, 3, 4, 5, 6, 7, 8, 9 or 33 or an active variant or fragment thereof. In still further embodiments, the expression construct employed to modulate the level of the RKD polypeptide comprises the polynucleotide set forth in SEQ ID NO: 1 or 3 or an active variant thereof operably linked to a the polynucleotide sequence encoding the polypeptide set forth in SEQ ID NO: 14 or an active variant or fragment thereof.
IX. Additional Methods of Use for Ovule Tissue-Preferred Promoter Sequences
The various ovule-tissue preferred promoter sequences disclosed herein, as well as variants and fragments thereof, are useful in the genetic manipulation of any plant when assembled with a DNA construct such that the promoter sequence is operably linked to a heterologous polynucleotide encoding a heterologous protein or an RNA of interest. In this manner, the nucleotide sequences of the ovule-tissue preferred promoter sequences are provided in expression cassettes along with heterologous polynucleotides for expression in the plant of interest.
Synthetic hybrid promoter regions are known in the art. Such regions comprise upstream promoter elements of one nucleotide sequence operably linked to the promoter element of another nucleotide sequence. In an embodiment of the disclosure, heterologous gene expression is controlled by a synthetic hybrid promoter comprising the ovule-tissue preferred promoter sequences disclosed herein, or a variant or fragment thereof, operably linked to upstream promoter element(s) from a heterologous promoter.
The ovule-tissue preferred promoter sequences and methods disclosed herein are useful in regulating expression of any heterologous nucleotide sequence in a host plant in order to vary the phenotype of a plant. Various changes in phenotype are of interest including modifying the fatty acid composition in a plant, altering the amino acid content of a plant, altering a plant's pathogen defense mechanism, and the like. These results can be achieved by providing expression of heterologous products or increased expression of endogenous products in plants. Alternatively, the results can be achieved by providing for a reduction of expression of one or more endogenous products, particularly enzymes or cofactors in the plant. These changes result in a change in phenotype of the transformed plant.
Genes of interest are reflective of the commercial markets and interests of those involved in the development of the crop. Crops and markets of interest change, and as developing nations open up world markets, new crops and technologies will emerge also. In addition, as our understanding of agronomic traits and characteristics such as yield and heterosis increase, the choice of genes for transformation will change accordingly. General categories of genes of interest include, for example, those genes involved in information, such as zinc fingers, those involved in communication, such as kinases, and those involved in housekeeping, such as heat shock proteins. More specific categories of transgenes, for example, include genes encoding important traits for agronomics, insect resistance, disease resistance, herbicide resistance, sterility, grain characteristics and commercial products. Genes of interest include, generally, those involved in oil, starch, carbohydrate or nutrient metabolism as well as those affecting kernel size, sucrose loading and the like.
X. Sequence Identity
The following terms are used to describe the sequence relationships between two or more nucleic acids or polynucleotides: (a) “reference sequence”, (b) “comparison window”, (c) “sequence identity”, (d) “percentage of sequence identity” and (e) “substantial identity”.
As used herein, “reference sequence” is a defined sequence used as a basis for sequence comparison. A reference sequence may be a subset or the entirety of a specified sequence; for example, as a segment of a full-length cDNA or gene sequence or the complete cDNA or gene sequence.
As used herein, “comparison window” makes reference to a contiguous and specified segment of a polynucleotide sequence, wherein the polynucleotide sequence in the comparison window may comprise additions or deletions (i.e., gaps) compared to the reference sequence (which does not comprise additions or deletions) for optimal alignment of the two sequences. Generally, the comparison window is at least 20 contiguous nucleotides in length, and optionally can be 30, 40, 50, 100 or longer. Those of skill in the art understand that to avoid a high similarity to a reference sequence due to inclusion of gaps in the polynucleotide sequence, a gap penalty is typically introduced and is subtracted from the number of matches.
Methods of alignment of sequences for comparison are well known in the art. Thus, the determination of percent sequence identity between any two sequences can be accomplished using a mathematical algorithm. Non-limiting examples of such mathematical algorithms are the algorithm of Myers and Miller, (1988) CABIOS 4:11-17; the algorithm of Smith, et al., (1981) Adv. Appl. Math. 2:482; the algorithm of Needleman and Wunsch, (1970) J. Mol. Biol. 48:443-453; the algorithm of Pearson and Lipman, (1988) Proc. Natl. Acad. Sci. 85:2444-2448; the algorithm of Karlin and Altschul, (1990) Proc. Natl. Acad. Sci. USA 872:264, modified as in Karlin and Altschul, (1993) Proc. Natl. Acad. Sci. USA 90:5873-5877, herein incorporated by reference in their entirety.
Computer implementations of these mathematical algorithms can be utilized for comparison of sequences to determine sequence identity. Such implementations include, but are not limited to: CLUSTAL in the PC/Gene program (available from Intelligenetics, Mountain View, Calif.); the ALIGN program (Version 2.0) and GAP, BESTFIT, BLAST, FASTA and TFASTA in the GCG Wisconsin Genetics Software Package®, Version 10 (available from Accelrys Inc., 9685 Scranton Road, San Diego, Calif., USA). Alignments using these programs can be performed using the default parameters. The CLUSTAL program is well described by Higgins, et al., (1988) Gene 73:237-244; Higgins, et al., (1989) CABIOS 5:151-153; Corpet, et al., (1988) Nucleic Acids Res. 16:10881-10890; Huang, et al., (1992) CABIOS 8:155-165 and Pearson, et al., (1994) Meth. Mol. Biol. 24:307-331, herein incorporated by reference in their entirety. The ALIGN program is based on the algorithm of Myers and Miller, (1988) supra. A PAM120 weight residue table, a gap length penalty of 12 and a gap penalty of 4 can be used with the ALIGN program when comparing amino acid sequences. The BLAST programs of Altschul, et al. (1990) J. Mol. Biol. 215:403, herein incorporated by reference in its entirety, are based on the algorithm of Karlin and Altschul, (1990) supra. BLAST nucleotide searches can be performed with the BLASTN program, score=100, word length=12, to obtain nucleotide sequences homologous to a nucleotide sequence encoding a protein of the disclosure. BLAST protein searches can be performed with the BLASTX program, score=50, word length=3, to obtain amino acid sequences homologous to a protein or polypeptide of the disclosure. To obtain gapped alignments for comparison purposes, Gapped BLAST (in BLAST 2.0) can be utilized as described in Altschul, et al., (1997) Nucleic Acids Res. 25:3389, herein incorporated by reference in its entirety. Alternatively, PSI-BLAST (in BLAST 2.0) can be used to perform an iterated search that detects distant relationships between molecules. See, Altschul, et al., (1997) supra. When utilizing BLAST, Gapped BLAST, PSI-BLAST, the default parameters of the respective programs (e.g., BLASTN for nucleotide sequences, BLASTX for proteins) can be used. See, the web site for the National Center for Biotechnology Information on the World Wide Web at ncbi.nlm.nih.gov. Alignment may also be performed manually by inspection.
Unless otherwise stated, sequence identity/similarity values provided herein refer to the value obtained using GAP Version 10 using the following parameters: % identity and % similarity for a nucleotide sequence using GAP Weight of 50 and Length Weight of 3, and the nwsgapdna.cmp scoring matrix; % identity and % similarity for an amino acid sequence using GAP Weight of 8 and Length Weight of 2 and the BLOSUM62 scoring matrix or any equivalent program thereof. As used herein, “equivalent program” is any sequence comparison program that, for any two sequences in question, generates an alignment having identical nucleotide or amino acid residue matches and an identical percent sequence identity when compared to the corresponding alignment generated by GAP Version 10.
The GAP program uses the algorithm of Needleman and Wunsch, supra, to find the alignment of two complete sequences that maximizes the number of matches and minimizes the number of gaps. GAP considers all possible alignments and gap positions and creates the alignment with the largest number of matched bases and the fewest gaps. It allows for the provision of a gap creation penalty and a gap extension penalty in units of matched bases. GAP must make a profit of gap creation penalty number of matches for each gap it inserts. If a gap extension penalty greater than zero is chosen, GAP must, in addition, make a profit for each gap inserted of the length of the gap times the gap extension penalty. Default gap creation penalty values and gap extension penalty values in Version 10 of the GCG Wisconsin Genetics Software Package® for protein sequences are 8 and 2, respectively. For nucleotide sequences the default gap creation penalty is 50 while the default gap extension penalty is 3. The gap creation and gap extension penalties can be expressed as an integer selected from the group of integers consisting of from 0 to 200. Thus, for example, the gap creation and gap extension penalties can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65 or greater.
GAP presents one member of the family of best alignments. There may be many members of this family, but no other member has a better quality. GAP displays four figures of merit for alignments: Quality, Ratio, Identity and Similarity. The Quality is the metric maximized in order to align the sequences. Ratio is the quality divided by the number of bases in the shorter segment. Percent Identity is the percent of the symbols that actually match. Percent Similarity is the percent of the symbols that are similar. Symbols that are across from gaps are ignored. A similarity is scored when the scoring matrix value for a pair of symbols is greater than or equal to 0.50, the similarity threshold. The scoring matrix used in Version 10 of the GCG Wisconsin Genetics Software Package® is BLOSUM62 (see, Henikoff and Henikoff, (1989) Proc. Natl. Acad. Sci. USA 89:10915, herein incorporated by reference in its entirety).
As used herein, “sequence identity” or “identity” in the context of two nucleic acid or polypeptide sequences makes reference to the residues in the two sequences that are the same when aligned for maximum correspondence over a specified comparison window. When percentage of sequence identity is used in reference to proteins it is recognized that residue positions which are not identical often differ by conservative amino acid substitutions, where amino acid residues are substituted for other amino acid residues with similar chemical properties (e.g., charge or hydrophobicity) and therefore do not change the functional properties of the molecule. When sequences differ in conservative substitutions, the percent sequence identity may be adjusted upwards to correct for the conservative nature of the substitution. Sequences that differ by such conservative substitutions are said to have “sequence similarity” or “similarity”. Means for making this adjustment are well known to those of skill in the art. Typically this involves scoring a conservative substitution as a partial rather than a full mismatch, thereby increasing the percentage sequence identity. Thus, for example, where an identical amino acid is given a score of one and a non-conservative substitution is given a score of zero, a conservative substitution is given a score between zero and one. The scoring of conservative substitutions is calculated, e.g., as implemented in the program PC/GENE (Intelligenetics, Mountain View, Calif.).
As used herein, “percentage of sequence identity” means the value determined by comparing two optimally aligned sequences over a comparison window, wherein the portion of the polynucleotide sequence in the comparison window may comprise additions or deletions (i.e., gaps) as compared to the reference sequence (which does not comprise additions or deletions) for optimal alignment of the two sequences. The percentage is calculated by determining the number of positions at which the identical nucleic acid base or amino acid residue occurs in both sequences to yield the number of matched positions, dividing the number of matched positions by the total number of positions in the window of comparison and multiplying the result by 100 to yield the percentage of sequence identity.
The term “substantial identity” of polynucleotide sequences means that a polynucleotide comprises a sequence that has at least 70% sequence identity, optimally at least 80%, more optimally at least 90% and most optimally at least 95%, compared to a reference sequence using an alignment program using standard parameters. One of skill in the art will recognize that these values can be appropriately adjusted to determine corresponding identity of proteins encoded by two nucleotide sequences by taking into account codon degeneracy, amino acid similarity, reading frame positioning and the like. Substantial identity of amino acid sequences for these purposes normally means sequence identity of at least 60%, 70%, 80%, 90% and at least 95%.
The following examples are offered by way of illustration and not by way of limitation.
EXAMPLES
The embodiments are further defined in the following Examples, in which parts and percentages are by weight and degrees are Celsius, unless otherwise stated. It should be understood that these Examples, while indicating embodiments of the disclosure, are given by way of illustration only. From the above discussion and these Examples, one skilled in the art can ascertain the essential characteristics of the embodiments, and without departing from the spirit and scope thereof, can make various changes and modifications of them to adapt to various usages and conditions. Thus, various modifications of the embodiments in addition to those shown and described herein will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.
The disclosure of each reference set forth herein is incorporated herein by reference in its entirety.
Example 1
Activity of the AT NUC1 Modified Promoter (ALT1)
PHP42329 was created to test the expression pattern of the AT-NUC1 PRO (ALT1) with a GUS reporter. Expression was found exclusively in the ovule and predominantly in the micropylar end. Expression also appeared to occur in the inner integuments. The results also indicated that expression is confined to the ovule very early in seed development and can be seen internally in the gynoecium. See, FIG. 1 .
Further more detailed work confirmed that expression was specific in the inner integument at the micropylar end prior to fertilization as early as the 4-8 nucleate stage of embryo sac development. The results further indicated that most ovules show GUS expression at their chalazal end at later stages of development. By the late globular stage, expression is still significant at the micropylar end of the ovule, but expression has moved to the chalazal end as well. At the heart-shaped embryo stage, a significant portion of expression can be noted in the outer and inner integuments of the chalazal end of the ovule. Weak expression can still be noted in the micropylar integuments at the heart-shaped embryo stage.
Mycropylar expression is advantageous for adventitious embryony and apospory since the native embryo forms at the micropylar end of the embryo sac. The AT NUC1 (ALT1) expression pattern envelopes the synergids and egg cell and is very near to, although not within the embryo sac. To demonstrate that the DNA sequence isolated as the AT NUC1 promoter functions as a promoter, transgenic Arabidopsis assays were performed. These assays provided a rapid assessment of whether the DNA sequence tested is able to direct gene expression.
Example 2
Activity of the Expression Cassette Comprising the AT-CYP86C1 Promoter Linked to DS-Red Reporter (PHP43541)
PHP43541 was created to test the expression pattern of the AT-CYP86C1 promoter with a RED fluorescent protein reporter. The promoter AT CYP86C1 (AT1G24540) demonstrates an expression pattern in the micropylar tip of the inner integument surrounding the micropylar half of the embryo sac in the egg stage. The outer integument at the extreme micropylar end of the outer integuments also show expression. Expression appears present from several days before pollination to several days after pollination. During development from the zygote stage to the late globular embryo stage, expression progressively spreads through the endothelial layer (innermost layer of the inner integument) towards the chalazal end of the ovule. By the heart-shaped embryo stage, the entire endothelial layer shows expression ( FIGS. 2 through 10 ).
Example 3
Activity of the Expression Cassette Comprising the AT-PPM1 Promoter Linked to ZS-GREEN (PHP48047)
The promoter AT PPM1 (AT5G49180) demonstrates two different types of expression patterns. First the AT-PPM1 promoter demonstrates an expression pattern in the extreme micropylar end of the inner and outer integuments, but not the epidermal layer of the outer integument. The second type of expression pattern is an extension of the first. Not only does the extreme micropylar inner and outer integuments (except for the epidermal layer) show expression, but expression extends chalazally to completely surround the entire embryo sac. The chalazal nucellus does not show expression ( FIG. 11 ).
Example 4
Activity of the Expression Cassette Comprising the AT-SLVL3 Promoter Linked to GUS (PHP43542)
The promoter AT SVL3 (AT3G20520) demonstrates an expression pattern that starts early during megagametogenesis. At the four-nucleate megagametophyte stage expression is initially strong in the micropylar inner and outer integuments, spreading throughout the integuments of the entire ovule. By the zygote stage, the strength of expression has increased in the integumentary tissues. Also, the endosperm and embryo now show weak expression. Expression is absent in the funiculus ( FIG. 12 ).
Example 5
Activity of the Expression Cassette Comprising the AT-EXT Promoter Linked to ZS-Green (PHP48049)
The promoter AT EXT (AT3G48580) demonstrates an expression pattern in the inner integuments and innermost layer of the outer integument surrounding the micropylar end of the embryo sac. In addition, in one example, a single cell (innermost layer of outer integument at the micropylar end) shows strong expression. No expression was noted within the embryo sac ( FIG. 13 ).
Example 6
Activity of the AT-NUC1 Promoter Comprising the AT-RKD2 Polynucleotide and Characterization of the Same when Expressed in Arabidopsis
The RKD expression cassette was molecularly stacked with AT-DD45-DSRED reporter construct (PHP50089 AT-NUC1 PRO (ALT1):AT-RKD2-AT-DD45 PRO:DsRed). Ectopic expression of RKD2 demonstrated an egg cell-like state in unreduced cells of the ovule outside of the embryo sac.
Many ovules from the ˜50% of the lines show one to six cells expressing the AT-DD45 PRO:DS-RED EXPRESS reporter in somatic cells in the ovule. Co-expression of the reporter construct with the RKD2 polypeptide in an ovule preferred manner demonstrated an egg-cell like transcriptional state induced in tissues and substructures suitable for adventitious embryony. Embryo-like structures have been observed in the integumentary space in ovules, suggesting an early stage of adventitious embryony. See, FIGS. 14 through 23 .
Example 8
Activity of the AT-CYP86C1 Promoter Comprising the AT-RKD2 Polynucleotide and Characterization of the Same when Expressed in Arabidopsis
The RKD expression cassette was molecularly stacked with AT-DD45-DSRED reporter construct (PHP50089 PHP50088 AT-CYP86C1 PRO:AT-RKD2-AT-DD45 PRO:DsRed). See, FIGS. 24 through 29 .
Ovules demonstrated multiple cells expressing the AT-DD45Pro-Red Express reporter in somatic cells in the ovule. Co-expression of the reporter construct with the RKD2 polypeptide in an ovule preferred manner demonstrated an egg-cell like transcriptional state induced in tissues and substructures suitable for adventitious embryony.
All publications and patent applications mentioned in the specification are indicative of the level of those skilled in the art to which this disclosure pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.
Although the foregoing disclosure has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims.