Genome-Wide Identification, Characterization and Expression Pattern Analysis of the γ-Gliadin Gene Family in the Durum Wheat (Triticum durum Desf.) Cultivar Svevo

Abstract

Very recently, the genome of the modern durum wheat cv. Svevo was fully sequenced, and its assembly is publicly available. So, we exploited the opportunity to carry out an in-depth study for the systematic characterization of the γ-gliadin gene family in the cv. Svevo by combining a bioinformatic approach with transcript and protein analysis. We found that the γ-gliadin family consists of nine genes that include seven functional genes and two pseudogenes. Three genes, Gli-γ1a, Gli-γ3a and Gli-γ4a, and the pseudogene Gli-γ2a* mapped on the A genome, whereas the remaining four genes, Gli-γ1b, Gli-γ2b, Gli-γ3b and Gli-γ5b, and the pseudogene Gli-γ4b* mapped on the B genome. The functional γ-gliadins presented all six domains and eight-cysteine residues typical of γ-gliadins. The Gli-γ1b also presented an additional cysteine that could possibly have a role in the formation of the gluten network through binding to HMW glutenins. The γ-gliadins from the A and B genome differed in their celiac disease (CD) epitope content and composition, with the γ-gliadins from the B genome showing the highest frequency of CD epitopes. In all the cases, almost all the CD epitopes clustered in the central region of the γ-gliadin proteins. Transcript analysis during seed development revealed that all the functional γ-gliadin genes were expressed with a similar pattern, although significant differences in the transcript levels were observed among individual genes that were sometimes more than 60-fold. A progressive accumulation of the γ-gliadin fraction was observed in the ripening seeds that reached 34% of the total gliadin fraction at harvest maturity. We believe that the insights generated in the present study could aid further studies on gliadin protein functions and future breeding programs aimed at the selection of new healthier durum wheat genotypes.