Geographical distribution and adaptive variation of VRN-A3 alleles in worldwide polyploid wheat (Triticum spp.) species collection

Main conclusion The distribution of early flowering alleles of VRN-A3 was found to be biased to low latitudes, and these alleles may contribute to environmental adaptability to low latitudes in cultivated emmer wheat. In wheat ( Triticum spp.), the flowering time is an important trait for successful seed production and yield by adapting to the regional environment. An early flowering allele of VRN-A3 with 7- and 25-bp insertions in the promoter region ( Vrn-A3a-h1 ) has recently been reported from the analysis of an emmer wheat ( Triticum turgidum L. ssp. dicoccum ) accession, TN26. This early flowering allele of VRN-A3 might be associated with the regional adaptation of wheat. In this study, we elucidated its geographic distribution to assess the importance of the early flowering allele of VRN-A3 in worldwide wheat collection. From sequence analysis, we identified six VRN-A3 alleles with the 7- and 25-bp insertions, namely, Vrn-A3a-h2 , Vrn-A3a-h3 , Vrn-A3a-h4 , Vrn-A3a-h5 , Vrn-A3a-h6 , and Vrn-A3c-h2 from wild emmer wheat, while we identified two VRN-A3 alleles with these insertions, Vrn-A3a-h2 and Vrn-A3c-h1 from cultivated tetraploid and hexaploid wheat species in addition to Vrn-A3a-h1 . Among VRN-A3 alleles distributed in cultivated wheat, we found that Vrn-A3a-h2 promoted early heading, whereas Vrn-A3c-h1 did not affect heading time. Our analysis showed that the distribution of early flowering alleles of VRN-A3 dominated in cultivated emmer wheat in Ethiopia and India, which actually showed an early flowering phenotype. This implied that the early flowering alleles of VRN-A3 contribute to adaptability to a low-latitude environment in cultivated emmer wheat. We could not find durum ( T . turgidum L. ssp. durum ) and bread wheat ( T. aestivum L. ssp. aestivum ) accessions with these early flowering alleles. Our findings indicated that Vrn-A3a-h1 and Vrn-A3a-h2 were useful for breeding of early flowering cultivars in durum and bread wheat varieties.