Evolution of Btr1-A Gene in Diploid Wheat Species of the Genus Triticum L.

During domestication of cereals, the threshability (hulled vs. naked grains) and brittle vs. non-brittle rachis were the most important traits, and man produced a breeding for naked and non-brittle rachis. In wheat, three gene systems that control the non-brittle rachis were identified. One of them is caused by the Btr1 (Non-brittle rachis) genes located in the chromosomes of the 3rd homeologic group. In the framework of this study, the sequences of the 5'- and 3'-untranslated regions and the coding region of the Btr1-A gene were studied for 30 accessions of wild and domesticated diploid wheat species Triticum boeoticum, T. monococcum, T. sinskajae, and T. urartu from Southern Europe, Transcaucasia, and Minor Asia. The Btr1-A gene sequence of T. sinskajae was obtained for the first time. In total, 11 various haplotypes of this gene were identified in the diploid wheat accessions studied, and five of them, namely, Hap12-Hap16, were described for the first time. The variability of T. boeoticum and T. urartu haplotypes, which were not previously described, does not affect the critical substitution at position 355 of the Btr1-A gene (G to A), specific to brittle rachis diploid wheat. The sequence of this gene in T. sinskajae and all T. monococcum accessions was identical to the haplotype Hap9 detected earlier. At position 355 of the Btr1-A gene, this haplotype replaces G with A, which leads to the occurrence of the non-brittle rachis trait. The involvement of diploid species haplotypes, which causes their lack of brittle rachis, in the naked polyploid wheat species is discussed.