Molecular Characterization and Variation of the Celiac Disease Epitope Domains among α-Gliadin Genes in Aegilops tauschii.

To explore the distribution and quantity of toxic epitopes in alpha-gliadins from Aegilops tauschii, a total of 133 complete alpha-gliadin coding sequences were obtained, including 69 pseudogenes with at least one premature stop codon and 64 genes with complete open reading frames (ORFs). Plenty of deletions and single amino acid substitutions were found in the 4 celiac disease (CD) toxic epitope domains through multiple alignments, in which the sequence of DQ2.5-glia-alpha 2 demonstrated the most significant changes. Interestingly, 7 of the 59 alpha-gliadins were free of any kind of intact CD toxic epitopes, providing potential gene resources for low CD toxicity breeding of common wheat. Analysis of the neighbor-joining tree demonstrates that 2 of the totally 7 alpha-gliadins cluster within the homologues of Triticum (A genome), and the other 5 group with those of Aegilops Sitopsis (B genome). This result implies that the 7 alpha-gliadin genes may be originated from the ancestor species of Ae. tauschii, evolved by the homoploid hybrid of Triticum and Aegilops Sitopsis. The remaining 52 alpha-gliadins form a separate Glade from other homologues of A and B genomes, suggesting a recent rapid gene expansion by gene duplication associated with the species adaptation.