PcG and trxG in plants – friends or foes

•Recent advances in epigenetic research challenge conventional notions of PcG- and trxG-mediated gene regulation.•Current thinking on PcG mechanism favors PRC2-independent recruitment of PRC1.•Arabidopsis has multiple PRC1 complexes. The chromatin compaction and histone ubiquitylation functions of PRC1 can be carried out via separate complexes.•trxG is known to antagonize PcG action, but also acts synergistically with PcG to inhibit gene expression.

The highly-conserved Polycomb group (PcG) and trithorax group (trxG) proteins play major roles in regulating gene expression and maintaining developmental states in many organisms. However, neither the recruitment of Polycomb repressive complexes (PRC) nor the mechanisms of PcG and trxG-mediated gene silencing and activation are well understood. Recent progress in Arabidopsis research challenges the dominant model of PRC2-dependent recruitment of PRC1 to target genes. Moreover, evidence indicates that diverse forms of PRC1, with shared components, are a common theme in plants and mammals. Although trxG is known to antagonize PcG, emerging data reveal that trxG can also repress gene expression, acting cooperatively with PcG. We discuss these recent findings and highlight the employment of diverse epigenetic mechanisms during development in plants and animals.