The vernalization gene VRN3 in wheat and barley is an orthologue of the FLOWERING LOCUS T (FT) gene in Arabidopsis. This study shows that VRN3 is linked to a gene similar to FT, and that the expression of the barley (HvFT) and wheat (TaFT) orthologues is significantly higher in plants with dominant Vrn3 alleles (early flowering) than in those with recessive vrn3 alleles (late flowering). In wheat, the dominant Vrn3 allele is associated with a retroelement insertion in the TaFT promoter, while in barley, mutations in the HvFT first intron differentiate plants with dominant and recessive VRN3 alleles. Transformation of winter wheat with the TaFT allele carrying the retroelement insertion resulted in earlier flowering, supporting the identity of TaFT with VRN-B3. Statistical analyses confirmed significant interactions between vernalization and FT allelic classes in both wheat and barley. These interactions were further supported by the up-regulation of HvFT transcript levels by vernalization in barley. These results confirm that the FT genes in wheat and barley are responsible for natural allelic variation in vernalization requirement, providing additional sources of adaptive diversity to these economically important crops. The study also shows that the FT gene is involved in the regulation of flowering time and that allelic variation in FT is associated with large differences in flowering time and significant interactions with vernalization requirements. The VRN3 gene is orthologous to the FT gene in Arabidopsis, and the study provides strong evidence supporting the identity between FT and VRN3 in wheat and barley. The study also shows that the VRN3 gene is involved in the regulation of flowering time and that allelic variation in VRN3 is associated with large differences in flowering time and significant interactions with vernalization requirements. The study also shows that the VRN3 gene is involved in the regulation of flowering time and that allelic variation in VRN3 is associated with large differences in flowering time and significant interactions with vernalization requirements.The vernalization gene VRN3 in wheat and barley is an orthologue of the FLOWERING LOCUS T (FT) gene in Arabidopsis. This study shows that VRN3 is linked to a gene similar to FT, and that the expression of the barley (HvFT) and wheat (TaFT) orthologues is significantly higher in plants with dominant Vrn3 alleles (early flowering) than in those with recessive vrn3 alleles (late flowering). In wheat, the dominant Vrn3 allele is associated with a retroelement insertion in the TaFT promoter, while in barley, mutations in the HvFT first intron differentiate plants with dominant and recessive VRN3 alleles. Transformation of winter wheat with the TaFT allele carrying the retroelement insertion resulted in earlier flowering, supporting the identity of TaFT with VRN-B3. Statistical analyses confirmed significant interactions between vernalization and FT allelic classes in both wheat and barley. These interactions were further supported by the up-regulation of HvFT transcript levels by vernalization in barley. These results confirm that the FT genes in wheat and barley are responsible for natural allelic variation in vernalization requirement, providing additional sources of adaptive diversity to these economically important crops. The study also shows that the FT gene is involved in the regulation of flowering time and that allelic variation in FT is associated with large differences in flowering time and significant interactions with vernalization requirements. The VRN3 gene is orthologous to the FT gene in Arabidopsis, and the study provides strong evidence supporting the identity between FT and VRN3 in wheat and barley. The study also shows that the VRN3 gene is involved in the regulation of flowering time and that allelic variation in VRN3 is associated with large differences in flowering time and significant interactions with vernalization requirements. The study also shows that the VRN3 gene is involved in the regulation of flowering time and that allelic variation in VRN3 is associated with large differences in flowering time and significant interactions with vernalization requirements.