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.