フロリゲン活性化複合体の細胞内イメージング(<特集>ライブセルイメージング)

抄録

Florigen is a systemic signal that promotes flowering. Its molecular nature is a conserved FLOWERING LOCUS T (FT)/ Heading date 3a (Hd3a) protein with small globular structure. FT/Hd3a protein is synthesized in leaves, transported into shoot apical meristem to initiate floral transition. Key question in this process is how florigen exerts this transition in the shoot apical cells. Imaging Hd3a proteins and its partner proteins in living cells revealed dynamic process regulating the formation of transcriptional protein complex in the nucleus. We developed two techniques for quantification of protein-protein interaction by bimolecular fluorescent complementation (BiFC) assay and for detection of tripartite protein complex by combining BiFC and foster resonance energy transfer (FRET), which is measured by fluorescence life-time imaging microscopy (FLIM). These techniques allow us to observe the formation of Hd3a-14-3-3-OsFD1 complex in living cells. Hd3a interacts with 14-3-3 proteins in the cytoplasm, then Hd3a-14-3-3 subcomplex translocates into the nucleus to interact with OsFD1 to yield a protein complex that we call florigen activation complex (FAC). The detailed imaging of another FD homolog, OsFD2, revealed that OsFD2 forms FAC in different way from that of OsFD1. These findings help further understanding of florigen function in living cells.