Structure and function of florigen and the receptor complex

In the 1930s, the flowering hormone, florigen, was proposed to be synthesized in leaves under inductive day length and transported to the shoot apex, where it induces flowering. More recently, generated genetic and biochemical data suggest that florigen is a protein encoded by the gene, FLOWERING LOCUS T (FT). A rice (Oryza sativa) FT homolog, Hd3a, interacts with the rice FD homolog, OsFD1, via a 14-3-3 protein. Formation of this tri-protein complex is essential for flowering promotion by Hd3a in rice. In addition, the multifunctionality of FT homologs, other than for flowering promotion, is an emerging concept. Here we review the structural and biochemical features of the florigen protein complex and discuss the molecular basis for the multifunctionality of FT proteins.