Exploring the alpha‐gliadin locus: the 33‐mer peptide with six overlapping coeliac disease epitopes in Triticum aestivum is derived from a subgroup of Aegilops tauschii

Abstract

Summary Most alpha‐gliadin genes of the Gli‐D2 locus on the D genome of hexaploid bread wheat (Triticum aestivum) encode for proteins with epitopes that can trigger coeliac disease (CD), and several contain a 33‐mer peptide with six partly overlapping copies of three epitopes, which is regarded as a remarkably potent T‐cell stimulator. To increase genetic diversity in the D genome, synthetic hexaploid wheat lines are being made by hybridising accessions of Triticum turgidum (AB genome) and Aegilops tauschii (the progenitor of the D genome). The diversity of alpha‐gliadins in A. tauschii has not been studied extensively. We analysed the alpha‐gliadin transcriptome of 51 A. tauschii accessions representative of the diversity in A. tauschii. We extracted RNA from developing seeds and performed 454 amplicon sequencing of the first part of the alpha‐gliadin genes. The expression profile of allelic variants of the alpha‐gliadins was different between accessions, and also between accessions of the Western and Eastern clades of A. tauschii. Generally, both clades expressed many allelic variants not found in bread wheat. In contrast to earlier studies, we detected the 33‐mer peptide in some A. tauschii accessions, indicating that it was introduced along with the D genome into bread wheat. In these accessions, transcripts with the 33‐mer peptide were present at lower frequencies than in bread wheat varieties. In most A. tauschii accessions, however, the alpha‐gliadins do not contain the epitope, and this may be exploited, through synthetic hexaploid wheats, to breed bread wheat varieties with fewer or no coeliac disease epitopes.

Multiple Wheat Genomes Reveal Novel Gli-2 Sublocus Location and Variation of Celiac Disease Epitopes in Duplicated α-Gliadin Genes

“…Our results not only reflect this subgenome specificity but also show that epitopes causing gluten-related reactions are unevenly distributed among accessions covering a wide range of wheat diversity (Walkowiak et al, 2020). The D subgenome is the only identified source of the toxic 33-mer epitope within bread wheat, and its presence has been detected at low frequency in the germplasm of the D progenitor Aegilops tauschii (Schaart et al, 2021). Current efforts to incorporate this knowledge into breeding safer varieties include the generation of synthetics and Gli-D2 deletion lines (Camerlengo et al, 2017;Li et al, 2018), the development of probes to quickly confirm the presence of reactive epitopes (Dubois et al, 2017), and the genome-editing to reduce the immunotoxic 33-mer (Sánchez-León et al, 2018).…”

The grain quality of wheat wild relatives in the evolutionary context

“…The 33mer peptide comprises the epitopes DQ2.5-glia-α1a and b, DQ2.5-glia-α2 and DQ2.5-glia-α3. The immunodominant 33mer fragment originates from the D genome (Schaart et al 2020 ). Therefore, diploid and tetraploid wheats might confer a less toxic immune response.…”

“…On the one hand, this suggests that the CD-triggering epitope in bread wheat originates from this geographic region, but on the other hand, it also underlines that there are many Ae. tauschii accessions which might contain less to no toxic peptide variants (Schaart et al 2020 ).…”

Characterization of a Wheat-Dasypyrum breviaristatum Chromosome Addition and Its Derived Progenies Carrying Novel Dasypyrum-Specific Gliadin Genes

“…The AS-PCR primers referred Li et al [32] were used for mapping and cloning of Dasypyrum specific α-gliadin genes, The alignment for the resulted α-gliadin genes was subjected to phylogenetic analysis by using the new version of the MEGA software [33]. The presence or absence of T cell stimulatory epitopes, the innate peptide p31-43 and the 33-mer peptide for gluten sensitive persons were detected from the ammino acid sequences of α-gliadin genes as reported [32,34,35].…”