Characterization and phylogenetic analysis of α gliadin gene sequences reveals significant genomic divergence in Triticeae species

Although the unique properties of wheat alpha-gliadin gene family are well characterized, little is known about the evolution and genomic divergence of alpha-gliadin gene family within the Triticeae. We isolated a total of 203 alpha-gliadin gene sequences from 11 representative diploid and polyploid Triticeae species, and found 108 sequences putatively functional. Our results indicate that alpha-gliadin genes may have possibly originated from wild Secale species, where the sequences contain the shortest repetitive domains and display minimum variation. A miniature inverted-repeat transposable element insertion is reported for the first time in alpha-gliadin gene sequence of Thinopyrum intermedium in this study, indicating that the transposable element might have contributed to the diversification of alpha-gliadin genes family among Triticeae genomes. The phylogenetic analyses revealed that the alpha-gliadin gene sequences of Dasypyrum, Australopyrum, Lophopyrum, Eremopyrumand Pseudoroengeria species have amplified several times. A search for four typical toxic epitopes for celiac disease within the Triticeae alpha-gliadin gene sequences showed that the alpha-gliadins of wild Secale, Australopyrum and Agropyron genomes lack all four epitopes, while other Triticeae species have accumulated these epitopes, suggesting that the evolution of these toxic epitopes sequences occurred during the course of speciation, domestication or polyploidization of Triticeae.