Characterization of Flowering Locus T2 (FT2) in Wheat and Brachypodium

The precise timing of the developmental transition from vegetative to reproductive growth (flowering) has a major impact on end yield potential and the adaptability of crop species. The two major external stimuli used by temperate cereals to coordinate flowering with seasonal changes are temperature and light, through the vernalization and photoperiod pathways. These pathways converge on Flowering Locus T1 (FT1). FT belongs to the small multigene PEBP family of which there are six FT-like members in wheat. While data suggests FT1 is a key gene in the induction of flowering, its deletion delays flowering less than one month, suggesting that other FT-like genes may have overlapping functions. In this study, we characterized FT2 homologs in the temperate grasses Brachypodium distachyon, barley and wheat using transgenic and mutant approaches. Transgenic Brachypodium and barley plants over-expressing FT2 flowered extremely early, confirming the role of FT2 as a floral promoter. Downregulation of FT2 by RNAi in Brachypodium was associated with a significant eight day delay in flowering and reduced seed set. Loss-of-function mutations in FT-A2 (alone or in combination with mutants for FT-B2) resulted in a small but significant delay in flowering in the field. Taken together these results indicate that FT2 is not essential for flowering, but it does contribute to the promotion of flowering in both Brachypodium and wheat. We also found that FT2 gene expression profiles differ from those of FT1, suggesting that these two genes may have independent roles in the regulation of flowering in temperate cereals.