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.