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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.


ARF gene family of maize and Arabidopsis. Maize genes up-regulated two-fold in the embryo-sac-enriched samples (and over 0.1 FPKM) compared to the surrounding ovule tissue are indicated in red, while the genes with higher expression in the surrounding ovule tissue than the embryo sac are indicated in blue. Genes indicated in orange have higher expression in the embryo sac than the surrounding ovule but either fall below the 0.1 FPKM cutoff or are only 1.5 to 2.0 fold higher in the embryo sac compared to the ovule. Family classes are given according to Xing et al. (2011). Branches with family members whose downregulation in Arabidopsis by an artificial microRNA (Pagnussat et al., 2009) caused abnormal embryo sac development are marked by red (strongly targeted) or orange (more weakly targeted) bars.
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Figure 4: ARF gene family of maize and Arabidopsis. Maize genes up-regulated two-fold in the embryo-sac-enriched samples (and over 0.1 FPKM) compared to the surrounding ovule tissue are indicated in red, while the genes with higher expression in the surrounding ovule tissue than the embryo sac are indicated in blue. Genes indicated in orange have higher expression in the embryo sac than the surrounding ovule but either fall below the 0.1 FPKM cutoff or are only 1.5 to 2.0 fold higher in the embryo sac compared to the ovule. Family classes are given according to Xing et al. (2011). Branches with family members whose downregulation in Arabidopsis by an artificial microRNA (Pagnussat et al., 2009) caused abnormal embryo sac development are marked by red (strongly targeted) or orange (more weakly targeted) bars.

Mentions: Gene families involved in auxin perception and response were also examined for embryo sac expression. Representatives of the TIR1, ARF, and IAA gene families have higher expression in the embryo-sac-enriched samples than the surrounding ovule (Tables S7–S9; Figure 4, Figures S6,S7). RNA-seq analysis revealed that nine of the thirty-five ARF genes are expressed 2-fold higher in the embryo-sac-enriched samples than the surrounding ovule tissue plus two more with a weaker increase in the embryo-sac-enriched samples (Table S8). The Class II ARF group is over-represented among ES up-regulated genes; seven of the eleven Class II genes have higher expression in the embryo sac enriched samples, while only two of the remaining twenty-four ARF genes do, both of which are in Class VI (Figure 4). The function of this clade in embryo sac development is unknown. In Arabidopsis, combined down-regulation of several ARF genes caused abnormal embryo sac development (Pagnussat et al., 2009), but the artificial microRNA targeting ARFs in this study did not cover the Class II group, which includes most of the genes with increased expression in the maize embryo-sac-enriched samples.


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

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

ARF gene family of maize and Arabidopsis. Maize genes up-regulated two-fold in the embryo-sac-enriched samples (and over 0.1 FPKM) compared to the surrounding ovule tissue are indicated in red, while the genes with higher expression in the surrounding ovule tissue than the embryo sac are indicated in blue. Genes indicated in orange have higher expression in the embryo sac than the surrounding ovule but either fall below the 0.1 FPKM cutoff or are only 1.5 to 2.0 fold higher in the embryo sac compared to the ovule. Family classes are given according to Xing et al. (2011). Branches with family members whose downregulation in Arabidopsis by an artificial microRNA (Pagnussat et al., 2009) caused abnormal embryo sac development are marked by red (strongly targeted) or orange (more weakly targeted) bars.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
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Figure 4: ARF gene family of maize and Arabidopsis. Maize genes up-regulated two-fold in the embryo-sac-enriched samples (and over 0.1 FPKM) compared to the surrounding ovule tissue are indicated in red, while the genes with higher expression in the surrounding ovule tissue than the embryo sac are indicated in blue. Genes indicated in orange have higher expression in the embryo sac than the surrounding ovule but either fall below the 0.1 FPKM cutoff or are only 1.5 to 2.0 fold higher in the embryo sac compared to the ovule. Family classes are given according to Xing et al. (2011). Branches with family members whose downregulation in Arabidopsis by an artificial microRNA (Pagnussat et al., 2009) caused abnormal embryo sac development are marked by red (strongly targeted) or orange (more weakly targeted) bars.
Mentions: Gene families involved in auxin perception and response were also examined for embryo sac expression. Representatives of the TIR1, ARF, and IAA gene families have higher expression in the embryo-sac-enriched samples than the surrounding ovule (Tables S7–S9; Figure 4, Figures S6,S7). RNA-seq analysis revealed that nine of the thirty-five ARF genes are expressed 2-fold higher in the embryo-sac-enriched samples than the surrounding ovule tissue plus two more with a weaker increase in the embryo-sac-enriched samples (Table S8). The Class II ARF group is over-represented among ES up-regulated genes; seven of the eleven Class II genes have higher expression in the embryo sac enriched samples, while only two of the remaining twenty-four ARF genes do, both of which are in Class VI (Figure 4). The function of this clade in embryo sac development is unknown. In Arabidopsis, combined down-regulation of several ARF genes caused abnormal embryo sac development (Pagnussat et al., 2009), but the artificial microRNA targeting ARFs in this study did not cover the Class II group, which includes most of the genes with increased expression in the maize embryo-sac-enriched samples.

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.