Identification and Characterization of the FLOWERING LOCUS T/TERMINAL FLOWER 1 Gene Family in Petunia

The phosphatidylethanolamine-binding protein (PEBP) gene family exists in all eukaryote kingdoms, with three subfamilies: FT (FLOWERING LOCUS T)-like, TFL1 (TERMINAL FLOWER 1)-like, and MFT (MOTHER OF FT AND TFL1)-like. FT genes promote flowering, TFL1 genes act as a repressor of the floral transition, and MFT genes have functions in flowering promotion and regulating seed germination. We identified and characterized orthologs of the Arabidopsis FT/TFL1 gene family in petunia to elucidate their expression patterns and evolution. Thirteen FT/TFL1-like genes were isolated from petunia, with the five FT-like genes mainly expressed in leaves. The circadian rhythms of five FT-like genes and PhCO (petunia CONSTANS ortholog) were figured out. The expression of PhFT1 was contrary to that of PhFT2, PhFT3, PhFT4, and PhFT5. PhCO had a circadian clock different from Arabidopsis CO, but coincided with PhFT1; it decreased in daytime and accumulated at night. Two of the FT-like genes with differential circadian rhythm and higher expression levels, PhFT1 and PhFT4, were used to transform Arabidopsis. Eventually, overexpressing PhFT1 strongly delayed flowering, whereas overexpression of PhFT4 produced extremely early-flowering phenotype. Different from previous reports, PhTFL1a, PhTFL1b, and PhTFL1c were relatively highly expressed in roots. Taken together, this study demonstrates that petunia FT-like genes, like FT, are able to respond to photoperiod. The expression pattern of FT/TFL1 gene family in petunia contributes to a new insight into the functional evolution of this gene family.