from Sandra N. Oliver and E. Jean Finnegan writing in Epigenetics: A Reference Manual:
Polycomb-group (PcG) complexes are essential regulators of plant development. These multiprotein complexes repress gene expression by establishing and maintaining trimethylation of lysine 27 at histone H3, a modification that is associated with repressive chromatin. Recent studies have indicated that plant PcG complexes regulate key genes involved in responses to low temperature. Vernalization is a long-term response to low temperatures whereby plants coordinate their seasonal flowering to occur after winter. In contrast, acclimation of plants to low temperatures, a key step in the establishment of frost tolerance, involves rapid activation of cold-acclimation genes. In this chapter, we describe the dynamics of PcG-mediated gene regulation underlying these two important agronomic traits that are triggered by low temperatures.
Further reading: Epigenetics: A Reference Manual