The Divergence of Flowering Time Modulated by Is Independent to Their Interaction and Binding Activities.

FLOWERING LOCUS T () and TERMINAL FLOWER1 () proteins share highly conserved amino acid residues but they play opposite regulatory roles in promoting and repressing the flowering response, respectively. Previous substitution models and functional analysis have identified several key amino acid residues which are critical for the promotion of flowering. However, the precise relationship between naturally occurring homologs and the mechanism of their role in flowering is still unclear. In this study, homologs from eight Rosaceae species, namely, and , were isolated. Three of these homologs were further characterized by functional analyses involving site-directed mutagenesis. The results showed that these homologs might have diverse functions despite sharing a high similarity of sequences or crystal structures. Functional analyses were conducted for the key FT amino acids, Tyr-85 and Gln-140. It revealed that homologs cannot promote flowering simply by substitution with key amino acid residues. Mutations of the IYN triplet motif within segment C of exon 4 can prevent the homolog from promoting the flowering. Furthermore, physical interaction of FT homologous or mutated proteins with the transcription factor FD, together with their lipid-binding properties analysis, showed that it was not sufficient to trigger flowering. Thus, our findings revealed that the divergence of flowering time modulating by homologs is independent to interaction and binding activities.