Flowering locus T (FT) is the major regulatory component controlling photoperiodic floral transition. It is expressed in guard cells and affects blue light-induced stomatal opening induced by the blue-light receptor phototropins phot1 and phot2. Twin sister of FT (TSF) , which is the closest homolog of FT, was transcribed in guard cells, and light-induced stomatal opening was repressed in tsf-1, a T-DNA insertion mutant of TSF.
