Functional diversification of <italic>Flowering Locus T</italic> homologs in soybean: <italic>GmFT1a</italic> and <italic>GmFT2a/5a</italic> have opposite roles in controlling flowering and maturation.

Summary: Soybean flowering and maturation are strictly regulated by photoperiod. Photoperiod‐sensitive soybean varieties can undergo flowering reversion when switched from short‐day (SD) to long‐day (LD) conditions, suggesting the presence of a ‘floral‐inhibitor’ under LD conditions. We combined gene expression profiling with a study of transgenic plants and confirmed that <italic>GmFT1a</italic>, soybean <italic>Flowering Locus T</italic> (<italic>FT</italic>) homolog, is a floral inhibitor. <italic>GmFT1a</italic> is expressed specifically in leaves, similar to the flowering‐promoting <italic>FT</italic> homologs <italic>GmFT2a/5a</italic>. However, in Zigongdongdou (ZGDD), a model variety for studying flowering reversion, <italic>GmFT1a</italic> expression was induced by LD but inhibited by SD conditions. This was unexpected, as it is the complete opposite of the expression of flowering promoters <italic>GmFT2a/5a</italic>. Moreover, the key soybean maturity gene <italic>E1</italic> may up‐regulate <italic>GmFT1a</italic> expression. It is also notable that <italic>GmFT1a</italic> expression was conspicuously high in late‐flowering varieties. Transgenic overexpression of <italic>GmFT1a</italic> delayed flowering and maturation in soybean, confirming that <italic>GmFT1a</italic> functions as a flowering inhibitor. This discovery highlights the complex impacts of the functional diversification of the <italic>FT</italic> gene family in soybean, and implies that antagonism between flowering‐inhibiting and flowering‐promoting <italic>FT</italic> homologs in this highly photoperiod‐sensitive plant may specify vegetative vs reproductive development. [ABSTRACT FROM AUTHOR]