Regulation of FT splicing by an endogenous cue in temperate grasses

Appropriate flowering timing is crucial for plant reproductive success. The florigen, FLOWERING LOCUS T (FT), interacts with 14-3-3 proteins and the bZIP transcription factor FD, functioning at core nodes in multiple flowering pathways. There are two FT homologues, FT1 and FT2, in Brachypodium distachyon. Here we show that FT2 undergoes age-dependent alternative splicing (AS), resulting in two splice variants (FT2 alpha and FT2 beta). The FT2 beta-encoded protein cannot interact with FD or 14-3-3s but is able to form heterodimers with FT2 alpha and FT1, thereby interfering with the florigen-mediated assembly of the flowering initiation complex. Notably, transgenic plants overproducing FT2 beta exhibit delayed flowering, while transgenic plants in which FT2 beta is silenced by an artificial microRNA display accelerated flowering, demonstrating a dominant-negative role of FT2 beta in flowering induction. Furthermore, we show that the AS splicing of FT2 is conserved in important cereal crops, such as barley and wheat. Collectively, these findings reveal a novel posttranscriptional mode of FT regulation in temperate grasses.