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

Bo Lv,Xiuli Han,Kun Li,Jorge Dubcovsky,Daolin Fu,Stephen Pearce,Shuyun Wang,Jiajie Wu,Fei Ni,Rebecca Nitcher,Pilar Hernandez

doi:10.1371/journal.pone.0094171

Bo Lv, Xiuli Han + Show 9 more

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https://doi.org/10.1371/journal.pone.0094171

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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.

Highlights

The optimization of flowering and seed production is critical for plant survival and, in seed crops, to maximize grain yields
In the Brachypodium transformation experiment using the FT1 overexpression (FT1OE) construct for Bd21-3 FT1cDNA driven by the maize UBIQUITIN promoter (Figure 1A), none of the 180 calli regenerated under long days (LD) (16 h light/8 h dark) and only two out of 100 calli regenerated under short days (SD) (8 h light/16 h dark), grew weakly, and eventually died
In this study we show that the ectopic expression of FLOWERING LOCUS T1 (FT1) under constitutive promoters results in precocious flowering of differentiating wheat and Brachypodium calli, bypassing the generation of normal vegetative tissues

Summary

Introduction

The optimization of flowering and seed production is critical for plant survival and, in seed crops, to maximize grain yields. Vernalization requirement is conferred by the genes VERNALIZATION1 (VRN1) [4,5], VRN2 [6], VRN3 [7], and VRN4 [8,9]. The VRN3 gene encodes a RAF kinase inhibitor-like protein with high similarity to Arabidopsis protein FLOWERING LOCUS T (FT) and is a flowering promoter [7]. This gene will be referred to hereafter as FT1 to differentiate it from other FT-like genes present in the temperate grasses ([12])

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