Seasonal and Diurnal Regulation of Flowering via an Epigenetic Mechanism in Arabidopsis thaliana

Successful plant reproduction requires the precise control of the onset of flowering, which involves the transition from the vegetative growth phase to the reproductive growth phase. As a facultative long-day annual species, Arabidopsis thaliana flowers after an exposure to low temperatures under long-day conditions. This seasonal and diurnal control of flowering involves various epigenetic regulatory activities. We herein review the mechanism underlying the relevant epigenetic regulation, with a focus on the two key flowering regulatory genes, FLOWERING LOCUS C (FLC) and FLOWERING LOCUS T (FT). The expression of FLC, which encodes a flowering repressor, is controlled via a complex epigenetic mechanism involving histone modifications and long noncoding RNAs to establish the "winter memory" of plants annually exposed to winter conditions. In contrast, the expression of FT, which encodes a flowering activator, is temporally regulated through the diurnal binding of polycomb group proteins to the FT promoter to ensure day-length-dependent flowering. Thus, flowering is robustly and dynamically mediated via an epigenetic mechanism to ensure it occurs at the most appropriate time.