The Floral Repressor BROTHER OF FT AND TFL1 (BFT) Modulates Flowering Initiation under High Salinity in Arabidopsis

Floral transition is coordinately regulated by both endogenous and exogenous cues to ensure reproductive success under fluctuating environmental conditions. Abiotic stress conditions, including drought and high salinity, also have considerable influence on this developmental process. However, the signaling components and molecular mechanisms underlying the regulation of floral transition by environmental factors have not yet been defined. In this work, we show that the Arabidopsis BROTHER OF FT AND TFL1 (BFT) gene, which encodes a member of the FLOWERING LOCUS T (FT)/TERMINAL FLOWER 1 (TFL1) family, regulates floral transition under conditions of high salinity. The BFT gene was transcriptionally induced by high salinity in an abscisic acid (ABA)-dependent manner. Transgenic plants overexpressing the BFT gene (35S:BFT) and BFT-deficient mutant (bft-2) plants were phenotypically indistinguishable from Col-0 plants in seed germination and seedling growth under high salinity. In contrast, although the floral transition was delayed significantly in Col-0 plants under high salinity, that of the bft-2 mutant was not affected by high salinity. We also observed that expression of the APETALA1 (AP1) gene was suppressed to a lesser degree in the bft-2 mutant than in Col-0 plants. Taken together, our observations suggest that BFT mediates salt stress-responsive flowering, providing an adaptive strategy that ensures reproductive success under unfavorable stress conditions.