Molecular dissection of the flowering process from induction to morphogenesis in Arabidopsis

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Molecular events in FD-dependent and FD-independent flowering pathways and long-distance action of FT gene products (mRNA, protein) have been investigated. As components of the FD-dependent pathway, several Ca-dependent protein kinases (CDPKs) which may phosphorylate a C-terminal CDPK site in FD in the shoot apex were identified as FD-interactors by yeast two-hybrid assays. Biochemical demonstration of phosphorylation of FD will be the important next step in the future research. Genetic interaction between fd mutation and other flowering-related mutations was analyzed in detail and papers are currently being prepared. As an important component of the FD-independent flowering pathway, SOC1 was identified as an immediate downstream target of FT in the shoot apex. Several TCP transcription factors were identified as FT-interactors by yeast two-hybrid assays and bi-molecular fluorescent complementation assays. The role of these TCPs in flowering is currently being investigated. The long-distance action of FT in promotion of flowering was demonstrated using a local transient induction system for FT and two-shoot Y-grafting of young seedlings. The transport of FT-T7 protein from a single leaf blade to the shot apex or from a donor scion to the shoot apex of a recipient stock plants within 24-48 hours was observed. By using a synthetic FT gene with extensive synonymous substitution of all the codons in a single ORF, it was clearly shown that the mRNA sequence/structure per se is not of vital importance for the long-distance action of FT. These results have led to a conclusion that the FT protein, not mRNA, is the component of florigen.