Publication Date:
2019-10-10
Description:
Polycomb group (PcG) proteins act as evolutionary conserved epigenetic mediators of cell identity because they repress transcriptional programs that are not required at particular developmental stages. Each tissue is likely to have a specific epigenetic profile, which acts as a blueprint for its developmental fate. A hallmark for Polycomb Repressive Complex 2 (PRC2) activity is trimethylated lysine 27 on histone H3 (H3K27me3). In plants, there are distinct PRC2 complexes for vegetative and reproductive development, and it was unknown so far whether these complexes have target gene specificity. The FERTILIZATION INDEPENDENT SEED (FIS) PRC2 complex is specifically expressed in the endosperm and is required for its development; loss of FIS function causes endosperm hyperproliferation and seed abortion. The endosperm nourishes the embryo, similar to the physiological function of the placenta in mammals. We established the endosperm H3K27me3 profile and identified specific target genes of the FIS complex with functional roles in endosperm cellularization and chromatin architecture, implicating that distinct PRC2 complexes have a subset of specific target genes. Importantly, our study revealed that selected transposable elements and protein coding genes are specifically targeted by the FIS PcG complex in the endosperm, whereas these elements and genes are densely marked by DNA methylation in vegetative tissues, suggesting that DNA methylation prevents targeting by PcG proteins in vegetative tissues.
Author Summary
Cell identity is established by the evolutionary conserved Polycomb group (PcG) proteins that repress transcriptional programs which are not required at particular developmental stages. The plant FERTILIZATION INDEPENDENT SEED (FIS) PcG complex is specifically expressed in the endosperm where it is essential for normal development. The endosperm nourishes the embryo, similar to the physiological function of the placenta in mammals. In this study, we established the cell type–specific epigenome profile of PcG activity in the endosperm. The endosperm has reduced levels of DNA methylation, and based on our data we propose that PcG proteins are specifically targeted to hypomethylated sequences in the endosperm. Among these endosperm-specific PcG targets are genes with functional roles in endosperm cellularization and chromatin architecture, implicating a fundamental role of PcG proteins in regulating endosperm development. Importantly, we identified transposable elements and genes among the specific PcG targets in the endosperm that are densely marked by DNA methylation in vegetative tissues, suggesting an antagonistic placement of DNA methylation and H3K27me3 at defined sequences.
Type:
Article
,
PeerReviewed
Format:
text
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