PRC1 is taking the lead in PcG repression.

Polycomb group (PcG) proteins constitute a major epigenetic mechanism for gene repression throughout the plant life. For a long time, the PcG mechanism has been proposed to follow a hierarchical recruitment of PcG repressive complexes (PRCs) to target genes in which the binding of PRC2 and the incorporation of H3 lysine 27 trimethyl marks led to recruitment of PRC1, which in turn mediated H2A monoubiquitination. However, recent studies have turned this model upside-down by showing that PRC1 activity can be required for PRC2 recruitment and H3K27me3 marking. Here, we review the current knowledge on plant PRC1 composition and mechanisms of repression, as well as its role during plant development.