Dual roles for FY in the regulation of FLC.

In Arabidopsis, the flowering decision is determined by multiple pathways that integrate information from both endogenous signals and environmental cues. The genes of the autonomous pathway promote flowering by suppressing the expression of the floral repressor FLOWERING LOCUS C (FLC). Thus, autonomous-pathway mutants have elevated levels of FLC and are late flowering. Previous work has shown that two autonomous pathway proteins, FCA and FY, physically interact and this interaction is important in the repression of FLC. Recent work from our laboratory has shown that a hypomorphic allele of FY (fy-5) can cause earlier or later flowering, depending on the genetic background. These results suggest that FY has the potential to act as both an activator and a repressor of FLC. The FLC-activating activity of FY appears to be FCA-independent, as fy-5 causes earlier flowering in an fca-null background. Here we present a speculative model that reconciles these opposing phenotypes by proposing a dual role for FY in the regulation of flowering time.