Epigenetic regulation of developmental timing in floral stem cells.

In mammalian stem cells, expression of differentiation genes is repressed by Polycomb Repressive group protein Complexes PRC1 and PRC2, which are associated with the trimethylated histone H3 lys27 (H3K27me3) repressive mark. This repression is transmitted through DNA replication to maintain pluripotency, and at the same time, it is reversible under appropriate conditions that promote differentiation. Recent studies of plant stem cells suggest that the H3K27me3 mark is also involved in stem cell differentiation and proliferation in Arabidopsis flowers. In flower development, stem cell activity is terminated by a feedback loop of transcriptional regulators only after the proper number of organ primordia is created. One transcriptional repressor in the feedback loop plays a key role in balancing proliferation and differentiation of floral stem cells, and the status of H3K27me3 at the locus is involved in controlling the timing of induction during development. This review will summarize and discuss recent work on PRC-mediated temporal regulation of stem cell differentiation in flower development.