From flour to flower: how Polycomb group proteins influence multiple aspects of plant development.

Cell identity and differentiation are determined by patterns of regulatory gene expression. Spatially and temporally regulated homeotic gene expression defines segment identities along the anterior-posterior axis of animal embryos. Polycomb group (PcG) proteins form a cellular memory system that maintains the repressed state of homeotic gene expression. Conserved PcG proteins control multiple aspects of Arabidopsis development and maintain homeotic gene repression. In animals, PcG proteins repress their target genes by modifying histone tails through deacetylation and methylation, generating a PcG-specific histone code that recruits other chromatin remodeling proteins to establish a stable, heritable mechanism of epigenetic expression control. Plant PcG proteins might function through a similar biochemical mechanism owing to their conserved structural and functional relationship to animal PcG proteins.