Roles of Polycomb complexes in regulating gene expression and chromatin structure in plants

ABSTRACT The evolutionary conserved Polycomb Group (PcG) repressive system comprises two central protein complexes, PcG repressive complex 1 (PRC1) and PRC2. These complexes, through the incorporation of histone modifications on chromatin, display an essential role for normal development in eukaryotes. During the last years, a significant effort has been made to characterize these complexes in the different kingdoms, finding that, despite there is remarkable functional and mechanistic conservation, some key molecular principles have diverged. In this review, we discuss the current view on the function of plant PcG complexes. We compare the composition of PcG complexes between animals and plants, highlighting the role of recently identified plant PcG accessory proteins, and discussing new roles of old known PcG partners. We also examine the mechanisms by which the repression is achieved and how these complexes are recruited to target genes. Finally, we consider the possible role of some plant PcG proteins in mediating local and long-range chromatin interactions, and thus, contributing to shape chromatin 3D architecture.