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Correlation between a loss of auxin signaling and a loss of proliferation in maize antipodal cells.

Chettoor AM, Evans MM - Front Plant Sci (2015)

Bottom Line: In contrast to auxin signaling, cytokinin signaling is absent in the embryo sac and instead occurs adjacent to but outside of the antipodal cells.Mutant analysis shows a correlation between a loss of auxin signaling and a loss of proliferation of the antipodal cells.The leaf polarity mutant Laxmidrib1 causes a lack of antipodal cell proliferation coupled with a loss of DR5 and PIN1a expression in the antipodal cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Biology, Carnegie Institution for Science Stanford, CA USA.

ABSTRACT
The plant life cycle alternates between two genetically active generations: the diploid sporophyte and the haploid gametophyte. In angiosperms the gametophytes are sexually dimorphic and consist of only a few cells. The female gametophyte, or embryo sac, is comprised of four cell types: two synergids, an egg cell, a central cell, and a variable number of antipodal cells. In some species the antipodal cells are indistinct and fail to proliferate, so many aspects of antipodal cell function and development have been unclear. In maize and many other grasses, the antipodal cells proliferate to produce a highly distinct cluster at the chalazal end of the embryo sac that persists at the apex of the endosperm after fertilization. The antipodal cells are a site of auxin accumulation in the maize embryo sac. Analysis of different families of genes involved in auxin biosynthesis, distribution, and signaling for expression in the embryo sac demonstrates that all steps are expressed within the embryo sac. In contrast to auxin signaling, cytokinin signaling is absent in the embryo sac and instead occurs adjacent to but outside of the antipodal cells. Mutant analysis shows a correlation between a loss of auxin signaling and a loss of proliferation of the antipodal cells. The leaf polarity mutant Laxmidrib1 causes a lack of antipodal cell proliferation coupled with a loss of DR5 and PIN1a expression in the antipodal cells.

No MeSH data available.


Related in: MedlinePlus

Cellularized maize embryo sacs showing expression in the antipodal cells of (A–F) DR5::RFP reporter, (G–M) PIN1a::PIN1a-YFP reporter, and (N–O) TCS::TOMATO reporter. The chalazal tip of the antipodal cell cluster is oriented toward the upper left. (A) Embryo sac just prior to cellularization. (B,C,G,H) Early post-cellularized embryo sac with 6–10 antipodal cells. (D–F;I–P) Mature embryo sacs. (B–E) DR5::RFP expression in the antipodal cells. (F) DR5::RFP expression in the sporophytic tissues of the nucellus. (C) Boxed region in (B). (H) Boxed region in (G). (O) Boxed region in (N). (P) Model for auxin and cytokinin signaling in the mature maize embryo sac. Red indicates region of highest auxin signaling; orange indicates moderate auxin signaling; and yellow indicates low auxin signaling plus cytokinin signaling. Dashed lines indicate boundary of antipodal cells. cc, central cell; e, egg cell. Arrow indicates micropylar nucellus, and arrowhead indicates integuments. Scale bar = 100 μm (A,B,F,G,M,N,P) and = 33 μm (C–E,H–L,O).
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Figure 3: Cellularized maize embryo sacs showing expression in the antipodal cells of (A–F) DR5::RFP reporter, (G–M) PIN1a::PIN1a-YFP reporter, and (N–O) TCS::TOMATO reporter. The chalazal tip of the antipodal cell cluster is oriented toward the upper left. (A) Embryo sac just prior to cellularization. (B,C,G,H) Early post-cellularized embryo sac with 6–10 antipodal cells. (D–F;I–P) Mature embryo sacs. (B–E) DR5::RFP expression in the antipodal cells. (F) DR5::RFP expression in the sporophytic tissues of the nucellus. (C) Boxed region in (B). (H) Boxed region in (G). (O) Boxed region in (N). (P) Model for auxin and cytokinin signaling in the mature maize embryo sac. Red indicates region of highest auxin signaling; orange indicates moderate auxin signaling; and yellow indicates low auxin signaling plus cytokinin signaling. Dashed lines indicate boundary of antipodal cells. cc, central cell; e, egg cell. Arrow indicates micropylar nucellus, and arrowhead indicates integuments. Scale bar = 100 μm (A,B,F,G,M,N,P) and = 33 μm (C–E,H–L,O).

Mentions: PIN1a has complex patterns in the antipodal cell cluster of mature maize embryo sacs (Figure 3 and Table 2). PIN1a-YFP is detectable early in antipodal cell development at least as early as the 6–10 cell stage in all but the most chalazal antipodal cells (Figures 3G,H). In later stages, the most common patterns of PIN1a-YFP expression are: expression throughout the antipodal cell cluster (Figure 3I), expression in all cells of the antipodal cell cluster except the most chalazal cell (Figure 3J), and expression in the micropylar portion of the antipodal cell cluster with multiple cells at the chalazal end lacking (or with reduced) expression of PIN1a-YFP (Figure 3K). Less frequently, PIN1a-YFP protein is expressed in all but the micropylar domain of antipodal cells or all but the center of the antipodal cell cluster. The least frequent pattern has PIN1a-YFP expression only in the center of the antipodal cell cluster. Using the positions of the cell walls with the strongest expression of PIN1a-YFP as a proxy for the direction of auxin flow the two most common patterns are outward from the antipodal cell cluster and away from the central cell or random within the antipodal cell cluster. These patterns suggest that the auxin efflux pattern is dynamic but within the antipodal cell cluster. Whether these patterns represent different stages in mature or nearly mature antipodal cell clusters is difficult to determine without being able to maintain their growth in vitro.


Correlation between a loss of auxin signaling and a loss of proliferation in maize antipodal cells.

Chettoor AM, Evans MM - Front Plant Sci (2015)

Cellularized maize embryo sacs showing expression in the antipodal cells of (A–F) DR5::RFP reporter, (G–M) PIN1a::PIN1a-YFP reporter, and (N–O) TCS::TOMATO reporter. The chalazal tip of the antipodal cell cluster is oriented toward the upper left. (A) Embryo sac just prior to cellularization. (B,C,G,H) Early post-cellularized embryo sac with 6–10 antipodal cells. (D–F;I–P) Mature embryo sacs. (B–E) DR5::RFP expression in the antipodal cells. (F) DR5::RFP expression in the sporophytic tissues of the nucellus. (C) Boxed region in (B). (H) Boxed region in (G). (O) Boxed region in (N). (P) Model for auxin and cytokinin signaling in the mature maize embryo sac. Red indicates region of highest auxin signaling; orange indicates moderate auxin signaling; and yellow indicates low auxin signaling plus cytokinin signaling. Dashed lines indicate boundary of antipodal cells. cc, central cell; e, egg cell. Arrow indicates micropylar nucellus, and arrowhead indicates integuments. Scale bar = 100 μm (A,B,F,G,M,N,P) and = 33 μm (C–E,H–L,O).
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Related In: Results  -  Collection

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Show All Figures
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Figure 3: Cellularized maize embryo sacs showing expression in the antipodal cells of (A–F) DR5::RFP reporter, (G–M) PIN1a::PIN1a-YFP reporter, and (N–O) TCS::TOMATO reporter. The chalazal tip of the antipodal cell cluster is oriented toward the upper left. (A) Embryo sac just prior to cellularization. (B,C,G,H) Early post-cellularized embryo sac with 6–10 antipodal cells. (D–F;I–P) Mature embryo sacs. (B–E) DR5::RFP expression in the antipodal cells. (F) DR5::RFP expression in the sporophytic tissues of the nucellus. (C) Boxed region in (B). (H) Boxed region in (G). (O) Boxed region in (N). (P) Model for auxin and cytokinin signaling in the mature maize embryo sac. Red indicates region of highest auxin signaling; orange indicates moderate auxin signaling; and yellow indicates low auxin signaling plus cytokinin signaling. Dashed lines indicate boundary of antipodal cells. cc, central cell; e, egg cell. Arrow indicates micropylar nucellus, and arrowhead indicates integuments. Scale bar = 100 μm (A,B,F,G,M,N,P) and = 33 μm (C–E,H–L,O).
Mentions: PIN1a has complex patterns in the antipodal cell cluster of mature maize embryo sacs (Figure 3 and Table 2). PIN1a-YFP is detectable early in antipodal cell development at least as early as the 6–10 cell stage in all but the most chalazal antipodal cells (Figures 3G,H). In later stages, the most common patterns of PIN1a-YFP expression are: expression throughout the antipodal cell cluster (Figure 3I), expression in all cells of the antipodal cell cluster except the most chalazal cell (Figure 3J), and expression in the micropylar portion of the antipodal cell cluster with multiple cells at the chalazal end lacking (or with reduced) expression of PIN1a-YFP (Figure 3K). Less frequently, PIN1a-YFP protein is expressed in all but the micropylar domain of antipodal cells or all but the center of the antipodal cell cluster. The least frequent pattern has PIN1a-YFP expression only in the center of the antipodal cell cluster. Using the positions of the cell walls with the strongest expression of PIN1a-YFP as a proxy for the direction of auxin flow the two most common patterns are outward from the antipodal cell cluster and away from the central cell or random within the antipodal cell cluster. These patterns suggest that the auxin efflux pattern is dynamic but within the antipodal cell cluster. Whether these patterns represent different stages in mature or nearly mature antipodal cell clusters is difficult to determine without being able to maintain their growth in vitro.

Bottom Line: In contrast to auxin signaling, cytokinin signaling is absent in the embryo sac and instead occurs adjacent to but outside of the antipodal cells.Mutant analysis shows a correlation between a loss of auxin signaling and a loss of proliferation of the antipodal cells.The leaf polarity mutant Laxmidrib1 causes a lack of antipodal cell proliferation coupled with a loss of DR5 and PIN1a expression in the antipodal cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Biology, Carnegie Institution for Science Stanford, CA USA.

ABSTRACT
The plant life cycle alternates between two genetically active generations: the diploid sporophyte and the haploid gametophyte. In angiosperms the gametophytes are sexually dimorphic and consist of only a few cells. The female gametophyte, or embryo sac, is comprised of four cell types: two synergids, an egg cell, a central cell, and a variable number of antipodal cells. In some species the antipodal cells are indistinct and fail to proliferate, so many aspects of antipodal cell function and development have been unclear. In maize and many other grasses, the antipodal cells proliferate to produce a highly distinct cluster at the chalazal end of the embryo sac that persists at the apex of the endosperm after fertilization. The antipodal cells are a site of auxin accumulation in the maize embryo sac. Analysis of different families of genes involved in auxin biosynthesis, distribution, and signaling for expression in the embryo sac demonstrates that all steps are expressed within the embryo sac. In contrast to auxin signaling, cytokinin signaling is absent in the embryo sac and instead occurs adjacent to but outside of the antipodal cells. Mutant analysis shows a correlation between a loss of auxin signaling and a loss of proliferation of the antipodal cells. The leaf polarity mutant Laxmidrib1 causes a lack of antipodal cell proliferation coupled with a loss of DR5 and PIN1a expression in the antipodal cells.

No MeSH data available.


Related in: MedlinePlus