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

Abstract

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