Structure and Formation Mechanisms of Polymorphism of Hordein-Coding Loci in Domesticated Barley (Hordeum vulgare L.)

Hordein polymorphism in 2244 barley accessions was studied using starch gel electrophoresis. A total of 1197 old local accessions from 22 countries located in the main centers of barley diversity and the bordering regions, 428 varieties cultivated in the territory of the former Soviet Union and Russian Federation from 1929 to 2019, and 619 varieties from Europe, Asia, America, and Africa were analyzed. For the hordeins encoded by the Hrd A locus, 156 variants of blocks of components were identified; 271 variants were detected for the Hrd B locus; and 5 variants were detected for the Hrd F locus. On the basis of the published data on the molecular mechanisms of hordein polymorphism formation and analysis of artificial mutants at the hordein-coding loci, we identified groups, or families, of phenotypically similar component blocks among A- and B-hordein variants. For HRD A, 12 families (AI-AXII) were identified, and for HRG B, 17 families (BI-BXVII) were identified. The families differ significantly in the number of block variants: for HRD A, from 5 (AXII) to 60 (AI); for HRD B, from 3 (BXVII) to 41 (BXII). It is suggested that the families with the largest number of A- and B-hordein variants are the most ancient in domesticated barley. The mosaic structure and irregular distribution of frequencies of HRD A and HRD B family variants in local populations of different countries was shown. We suggested that the emergence of the HRD A and HRD B families was due to the spontaneous hybridization between H. vulgare and H. spontaneum during the spreading of domesticated barley. It is concluded that hordein polymorphism in domesticated barley resulted from spontaneous hybridization between the cultivated barley with a wild ancestor and accumulation of mutations in the genes at Hrd A and Hrd B loci in H. vulgare.