Characterization of FLOWERING LOCUS T1 (FT1) Gene in Brachypodium and Wheat

Abstract

The phase transition from vegetative to reproductive growth is a critical event in the life cycle of flowering plants. FLOWERING LOCUS T (FT) plays a central role in the regulation of this transition by integrating signals from multiple flowering pathways in the leaves and transmitting them to the shoot apical meristem. In this study, we characterized FT homologs in the temperate grasses Brachypodium distachyon and polyploid wheat using transgenic and mutant approaches. Downregulation of FT1 by RNAi was associated with a significant downregulation of the FT-like genes FT2 and FT4 in Brachypodium and FT2 and FT5 in wheat. In a transgenic wheat line carrying a highly-expressed FT1 allele, FT2 and FT3 were upregulated under both long and short days. Overexpression of FT1 caused extremely early flowering during shoot regeneration in both Brachypodium and hexaploid wheat, and resulted in insufficient vegetative tissue to support the production of viable seeds. Downregulation of FT1 transcripts by RNA interference (RNAi) resulted in non-flowering Brachypodium plants and late flowering plants (2–4 weeks delay) in wheat. A similar delay in heading time was observed in tetraploid wheat plants carrying mutations for both FT-A1 and FT-B1. Plants homozygous only for mutations in FT-B1 flowered later than plants homozygous only for mutations in FT-A1, which corresponded with higher transcript levels of FT-B1 relative to FT-A1 in the early stages of development. Taken together, our data indicate that FT1 plays a critical role in the regulation of flowering in Brachypodium and wheat, and that this role is associated with the simultaneous regulation of other FT-like genes. The differential effects of mutations in FT-A1 and FT-B1 on wheat heading time suggest that different allelic combinations of FT1 homoeologs could be used to adjust wheat heading time to improve adaptation to changing environments.

PHYTOCHROME C plays a major role in the acceleration of wheat flowering under long-day photoperiod

“…The delay in heading time observed in the tetraploid phyC AB mutant under LD is more than threefold longer than that observed in the triple ppd1-null mutant in hexaploid wheat (42) and that reported for the FT1 mutants in tetraploid Kronos (43). This result suggests that additional genes regulated by PHYC contribute to early flowering of wheat under LD.…”

“…Under LD, PPD1/PRR37 up-regulates FT1 in barley and wheat (25) but down-regulates FT homologs in rice and sorghum (58,59). Upregulation of FT1 in wheat is associated with the up-regulation of FT2 (43,71), which also promotes flowering (72). (Pathway B) PHYC also modulates the expression of circadian clock and clock output genes CO1 and CO2.…”

PHYTOCHROME C Is an Essential Light Receptor for Photoperiodic Flowering in the Temperate Grass, Brachypodium distachyon

“…Although there are several FT homologs in Brachypodium, a recent study indicates that one of them, which is phylogenetically most closely related to Arabidopsis FT, is the primary promoter of flowering, as knockdown of its expression results in a severe delay of flowering (Lv et al 2014). We have shown that this FT homolog is not expressed in phyC mutants and that overexpression of this FT is able to rescue the delayed flowering phenotype of phyC.…”

“…FT enhances VRN1 expression, "locking in" VRN2 repression and the promotion of flowering (Yan et al 2006;Shimada et al 2009). The proposed feedback model resulting from studies in wheat and barley appears to be largely conserved in Brachypodium (Lv et al 2014;Ream et al 2014) except that the role of VRN2L is less clear as it is up-regulated in the cold .…”

The expression patterns of threeVRNgenes in common wheat (Triticum aestivumL.) in response to vernalization

“…The insertion of a repetitive element in the regulatory region of Vrn-B3 in wheat variety Chinese Hope produces a dominant allele and early flowering. Transgenic winter wheat overexpressing the Vrn-B3 allele flowers earlier than the control without vernalization treatment (Yan et al 2006), suggesting that the dominant VRN3 allele can overcome the repression of VRN2 and bypass the vernalization requirement, while downregulation of FT1 expression by RNA interference results in late flowering in wheat (Lv et al 2014).…”