Increased copy number at the HvFT1 locus is associated with accelerated flowering time in barley

A precise regulation of flowering time is critical for plant reproductive success, and therefore, a better understanding of the natural variation in genes regulating the initiation of the reproductive phase is required to develop well-adapted varieties. In both monocot and dicot species, the FLOWERING LOCUS T (FT) is a central integrator of seasonal signals perceived by the leaves. The encoded mobile protein (florigen) is transmitted to the apical meristem where it induces flowering. The FT homolog in barley (Hordeum vulgare L.), designated HvFT1, was shown to correspond to the vernalization locus VRN-H3, and natural alleles for spring and winter growth habit were identified. In this study, we demonstrate that the HvFT1 allele present in the barley genetic stock (BGS213) associated with a dominant spring growth habit carries at least four identical copies of HvFT1, whereas most barley varieties have a single copy. Increased copy number is associated with earlier transcriptional up-regulation of HvFT1 and a spring growth habit. This allele is epistatic to winter alleles for VRN-H1 and VRN-H2. Among accessions with one HvFT1 copy, haplotype differences in the HvFT1 promoter and first intron are also associated with differences in flowering time, which are modulated by genetic background. These different HvFT1 alleles can be used to develop barley varieties adapted to different or changing environments. Our results, together with studies of other wheat and barley flowering genes, show that copy number variation plays an important role in the regulation of developmental processes in the temperate cereals.