Molecular characterization and dynamic expression patterns of two types of γ-gliadin genes from Aegilops and Triticum species

Gliadins were the major components of wheat storage proteins and determine the extensibility properties of gluten dough. In this work, 19 new full-length γ-gliadin genes were isolated from various Aegilops and Triticum species. Sequence characterization showed that a specific octapeptide and celiac disease (CD)-toxic epitope Gliγ-3 (VQGQGIIQPQQPAQL) were present in the rich glutamine domain and C-terminal non-repetitive domain, respectively. Based on the sequence features of both peptides, a new classification system for γ-gliadin gene family was established, in which γ-gliadins were classified into two types (types I and II) with each consisting of two groups. An uneven distribution of different types and groups of γ-gliadin genes was exhibited among 11 Aegilops and Triticum genomes. Phylogenetic analysis revealed that types I and II genes diverged at about 14 MYA while the divergence of 4 γ-gliadin group genes occurred at around 10 MYA almost simultaneously. The γ-gliadin genes from S^l and B genomes displayed a different transcriptional expression pattern during grain development, and rapid increasing of gliadin mRNA and proteins occurred at 15-20 DPA. In addition, genome-specific variations of CD-toxic epitopes among Aegilops and Triticum genomes were found. The A genome and its related progenitor genomes A^u and A^m had fewer CD epitopes than other genomes, suggesting that these genomes might be valuable gene resources to remove CD toxic peptides for wheat quality improvement.