The polycomb complex PRC1: composition and function in plants.

Polycomb group (PcG) proteins are crucial epigenetic regulators conferring transcriptional memory to cell lineages. They assemble into multi-protein complexes, e.g., Polycomb Repressive Complex 1 and 2 (PRC1, PRC2), which are thought to act in a sequential manner to stably maintain gene repression. PRC2 induces histone H3 lysine 27 (H3K27) trimethylation (H3K27me3), which is subsequently read by PRC1 that further catalyzes H2A monoubiquitination (H2Aub1), creating a transcriptional silent chromatin conformation. PRC2 components are conserved in plants and have been extensively characterized in Arabidopsis. In contrast, PRC1 composition and function are more diverged between animals and plants. Only more recently, PRC1 existence in plants has been documented. Here we review the aspects of plant specific and conserved PRC1 and highlight critical roles of PRC1 components in seed embryonic trait determinacy, shoot stem cell fate determinacy, and flower development in Arabidopsis.