Expansion of the gamma-gliadin gene family in Aegilops and Triticum

Abstract

BackgroundThe gamma-gliadins are considered to be the oldest of the gliadin family of storage proteins in Aegilops/Triticum. However, the expansion of this multigene family has not been studied in an evolutionary perspective.ResultsWe have cloned 59 gamma-gliadin genes from Aegilops and Triticum species (Aegilops caudata L., Aegilops comosa Sm. in Sibth. & Sm., Aegilops mutica Boiss., Aegilops speltoides Tausch, Aegilops tauschii Coss., Aegilops umbellulata Zhuk., Aegilops uniaristata Vis., and Triticum monococcum L.) representing eight different genomes: Am, B/S, C, D, M, N, T and U. Overall, 15% of the sequences contained internal stop codons resulting in pseudogenes, but this percentage was variable among genomes, up to over 50% in Ae. umbellulata. The most common length of the deduced protein, including the signal peptide, was 302 amino acids, but the length varied from 215 to 362 amino acids, both obtained from Ae. speltoides. Most genes encoded proteins with eight cysteines. However, all Aegilops species had genes that encoded a gamma-gliadin protein of 302 amino acids with an additional cysteine. These conserved nine-cysteine gamma-gliadins may perform a specific function, possibly as chain terminators in gluten network formation in protein bodies during endosperm development. A phylogenetic analysis of gamma-gliadins derived from Aegilops and Triticum species and the related genera Lophopyrum, Crithopsis, and Dasypyrum showed six groups of genes. Most Aegilops species contained gamma-gliadin genes from several of these groups, which also included sequences from the genera Lophopyrum, Crithopsis, and Dasypyrum. Hordein and secalin sequences formed separate groups.ConclusionsWe present a model for the evolution of the gamma-gliadins from which we deduce that the most recent common ancestor (MRCA) of Aegilops/Triticum-Dasypyrum-Lophopyrum-Crithopsis already had four groups of gamma-gliadin sequences, presumably the result of two rounds of duplication of the locus.

Gene editing towards hypoimmunogenic gluten proteins in wheat

“…Six groups of pseudogenes were observed that did not simply contain an early stop codon but also had divergent sequences compared to the 6 groups of full length γ-gliadins. is is consistent with the hypothesis of Goryunova et al (2012) that the various γ-gliadin groups largely predate the evolution of the genomes within the genus Triticum/Aegilops. Consequently, sgRNA were designed focusing on full length genes while considering pseudogenes as much as possible.…”

Genome-, Transcriptome- and Proteome-Wide Analyses of the Gliadin Gene Families in Triticum urartu

“…Numerous gliadin genes have been characterized using genomic DNA, EST and BAC libraries from common wheat and its relatives [ 25 – 27 , 31 ]. With the conserved PCR primers, 701 α-gliadin genes were collected from 29 diploid Triticeae species [ 31 ].…”

“…The gliadin genes have generally been isolated from genomic DNA, expressed sequence tag (EST) and bacterial artificial chromosome (BAC) libraries [ 25 – 27 ]. However, the identification of the full complement of gliadin gene family members in common wheat and its relatives remains challenging because of the large sizes of these gene families, the similar genetic structure within a family and the lack of genomic data [ 28 ].…”

Wheat Seed Proteins: Factors Influencing Their Content, Composition, and Technological Properties, and Strategies to Reduce Adverse Reactions

“…In theory, any gluten peptide comprising more than nine amino acids can potentially elicit an immune reaction in susceptible individuals (Osorio et al, 2012). Since no wheat genotypes are entirely gluten-free, no recent or old wheat varieties, landraces, or related diploid and tetraploid species or progenitors can be considered "coeliac-safe" (Brouns, Van Rooy, Shewry, Rustgi, & Jonkers, 2019;Brouns, van Buul, & Shewry, 2013;Goryunova et al, 2012;Mitea et al, 2010;Shewry, 2018--accompanying review). Support for this conclusion comes from wide genetic screens of wheat and related species for their immunogenic potential.…”