Abstract
The seed protein α-gliadin is a major component of wheat flour and causes gluten-related diseases. However, due to the complexity of this multigene family with a genome structure composed of dozens of copies derived from tandem and genome duplications, little was known about the variation between accessions, and thus little effort has been made to explicitly target α-gliadin for bread wheat breeding. Here, we analyzed genomic variation in α-gliadins across 11 recently published chromosome-scale assemblies of hexaploid wheat, with validation using long-read data. We unexpectedly found that the Gli-B2 locus is not a single contiguous locus but is composed of two subloci, suggesting the possibility of recombination between the two during breeding. We confirmed that the number of immunogenic epitopes among 11 accessions varied. The D subgenome of a European spelt line also contained epitopes, in agreement with its hybridization history. Evolutionary analysis identified amino acid sites under diversifying selection, suggesting their functional importance. The analysis opens the way for improved grain quality and safety through wheat breeding.
Highlights
Since its origin by allopolyploidization, bread wheat (Triticum aestivum L.) has become a staple crop, providing ∼20% of the calories consumed globally (Shiferaw et al, 2013)
Gene copy number variation and other differences in α-gliadins may be linked to the phenotypic differences for the wheat flour qualities among the cultivars, little is known about precise genomic information for the Gli2 loci to provide a basis for comparison between cultivars
In LongReach Lancer and Chinese Spring (CS), we could not identify α-gliadin copies on chromosome 6D; those found in scaffolds that were not anchored to a chromosome were assigned to Gli-D2 following the suggestion of Juhász et al (2018)
Summary
Since its origin by allopolyploidization, bread wheat (Triticum aestivum L.) has become a staple crop, providing ∼20% of the calories consumed globally (Shiferaw et al, 2013). Copy number variation, and expression differences in α-gliadins in bread wheat have been attributed to the combination of tandem and whole genome duplications (Salentijn et al, 2009; Noma et al, 2016; Huo et al, 2018). Gene copy number variation and other differences in α-gliadins may be linked to the phenotypic differences for the wheat flour qualities among the cultivars, little is known about precise genomic information for the Gli loci to provide a basis for comparison between cultivars. Sequence-based characterization of α-gliadin variation within modern hexaploid wheat cultivars will aid in breeding efforts to incorporate both desired end-use quality and lower reactivity for consumers
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