FLC or not FLC: the other side of vernalization.

Vernalization is the promotion of the competence for flowering by long periods of low temperatures such as those typically experienced during winters. In Arabidopsis, the vernalization response is, to a large extent, mediated by the repression of the floral repressor FLC, and the stable epigenetic silencing of FLC after cold treatments is essential for vernalization. In addition to FLC, other vernalization targets exist in Arabidopsis. In grasses, vernalization seems to be entirely independent of FLC. Here, the current understanding of FLC-independent branches of the vernalization pathway in Arabidopsis and vernalization without FLC in grasses is discussed. This review focuses on the role of AGL19, AGL24, and the MAF genes in Arabidopsis. Interestingly, vernalization acts through related molecular machineries on distinct targets. In particular, protein complexes similar to Drosophila Polycomb Repressive Complex 2 play a prominent role in establishing an epigenetic cellular memory for cold-regulated expression states of AGL19 and FLC. Finally, the similar network topology of the apparently independently evolved vernalization pathways of grasses and Arabidopsis is discussed.