Flowering-time Gene FD Encodes a bZIP Protein Which is Required for the Function of a Floral Pathway Integrator FT

Abstract

Flowering in Arabidopsis is regulated by several interacting pathways which are integrated by genes such as FT, SOC1/AGL20, and LFY to finally execute the floral transition. We have been interested in factors acting downstream of FT. The late-flowering gene FD is a good candidate for such genes. The FD activity seems to be required for the precocious-flowering phenotype of 35S::FT, because otherwise very weak fd-1 mutation strongly suppresses 35S::FT phenotype. Suppression effect of fd-1 is specific to FT, because fd-1 does not strongly affect early-flowering phenotype caused by overexpression of LFY or SOC1/AGL20. FD encodes a bZIP transcription factor of the ABF/AREB/GBF4 subclass. FD is expressed at very low level in LD and SD conditions. FD protein can interact with FT protein in yeast cells. These results suggest that FT is likely to play a key role in regulation of FD function by protein-protein interaction.