Regulation of cell identity by plant Polycomb and trithorax group proteins.

Descendants of stem cells have to make the decision whether to differentiate or whether to maintain a proliferation-competent state. This decision is mediated by the balanced activity of Polycomb group (PcG) and trithorax group (trxG) proteins. PcG proteins keep genes in a transcriptional repressed state while trxG proteins antagonize PcG activity and maintain genes in a transcriptional active state. PcG proteins act as global regulators of genomic programs that prevent the untimely expression of genes during development and, therefore, ensure that a correct set of genes is active during defined stages of development. Here we will discuss the recent progress in our understanding of the action of PcG proteins and the factors that antagonize PcG function to control cell fate and differentiation during plant development.