The less genetic diversity of Triticeae A and D genomes, the smaller diversity in γ-prolamins CD-epitopes

Abstract

Triticeae γ-type seed prolamins have undergone many rounds of gene duplications during evolution. However, the population genetics of total Triticeae γ-prolamin genes has not been studied in an evolutionary perspective so far. Here, evolutionary pattern of γ-prolamin multigene family containing 557 sequences from wheat and closely related species (γ-gliadins), rye (γ-secalin) and barley (γ-hordeins) was investigated. Furthermore, Triticeae genomes were searched for low immuno-reactive celiac disease (CD) epitope contents in their γ-prolamins for the possibility of developing less immunogenic cultivars. Large numbers of haplotypes with segregating sites and mutations in γ-type seed prolamin multigene family were evident. Polymorphism analyses of both promoters and coding regions of species-specific γ-prolamins demonstrated no deviation from neutral theory. The sliding window revealed that most of the singleton polymorphic sites are resided in the variable R1 domain. Furthermore, the significant negative Tajima’s D and H tests’ values of each groups 1, 2, 3, and 8 showed a selective sweep for R and D genome duplication processes. The dN/dS ratio analysis revealed strong purifying selection acting upon duplication of the two ancestral branches, while the neutral selection among overall groups was observed. Our results support previously reported findings that the groups of 2, 3, 8 (D genome) and 10 (A genome) can potentially be recommended for selection approaches or genetic engineering of less immunogenic cereal grains. Furthermore, the results provide new insights on the evolutionary dynamics of γ-prolamin multigene family, polyploidy speciation and phylogeny of Triticeae species.