Two FLX family members are non-redundantly required to establish the vernalization requirement in Arabidopsis

Studies of natural genetic variation for the vernalization requirement in Arabidopsis have revealed two genes, FRIGIDA (FRI) and FLOWERING LOCUS C (FLC), that are determinants of the vernalization-requiring, winter-annual habit. In this study, we show that FLC EXPRESSOR LIKE 4 (FLL4) is essential for up-regulation of FLC in winter-annual Arabidopsis accessions and establishment of a vernalization requirement. FLL4 is part of the FLC EXPRESSOR (FLX) gene family and both are non-redundantly involved in flowering-time control. Epistasis analysis among FRI, FLL4, FLX and autonomous-pathway genes reveals that FRI fve exhibits an extreme delay of flowering compared to fri fve, but mutants in other autonomous-pathway genes do not, indicating that FVE acts most antagonistically to FRI. FLL4 may represent a new member of a FRI-containing complex that activates FLC.