Functional diversification of Flowering Locus T homologs in soybean: GmFT1a and GmFT2a/5a 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 Gm FT 1a , soybean Flowering Locus T ( FT ) homolog, is a floral inhibitor. Gm FT 1a is expressed specifically in leaves, similar to the flowering‐promoting FT homologs Gm FT 2a/5a . However, in Zigongdongdou ( ZGDD ), a model variety for studying flowering reversion, Gm FT 1a 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 Gm FT 2a/5a . Moreover, the key soybean maturity gene E1 may up‐regulate Gm FT 1a expression. It is also notable that Gm FT 1a expression was conspicuously high in late‐flowering varieties. Transgenic overexpression of Gm FT 1a delayed flowering and maturation in soybean, confirming that Gm FT 1a functions as a flowering inhibitor. This discovery highlights the complex impacts of the functional diversification of the FT gene family in soybean, and implies that antagonism between flowering‐inhibiting and flowering‐promoting FT homologs in this highly photoperiod‐sensitive plant may specify vegetative vs reproductive development.