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Abstract
BackgroundΑ-gliadins form a multigene protein family encoded by multiple α-gliadin (Gli-2) genes at three genomic loci, Gli-A2, Gli-B2 and Gli-D2, respectively located on the homoeologous wheat chromosomes 6AS, 6BS, and 6DS. These proteins contain a number of important celiac disease (CD)-immunogenic domains. The α-gliadins expressed from the Gli-B2 locus harbour fewer conserved CD-epitopes than those from Gli-A2, whereas the Gli-D2 gliadins have the highest CD-immunogenic potential. In order to detect differences in the highly CD-immunogenic α-gliadin fraction we determined the relative expression level from the homoeologous Gli-2 loci in various tetraploid and hexaploid wheat genotypes by using a quantitative pyrosequencing method and by analyzing expressed sequence tag (EST) sequences.ResultsWe detected large differences in relative expression levels of α-gliadin genes from the three homoeologous loci among wheat genotypes, both as relative numbers of expressed sequence tag (EST) sequences from specific varieties and when using a quantitative pyrosequencing assay specific for Gli-A2 genes. The relative Gli-A2 expression level in a tetraploid durum wheat cultivar ('Probstdorfer Pandur') was 41%. In genotypes derived from landraces, the Gli-A2 frequency varied between 12% and 58%. In some advanced hexaploid bread wheat cultivars the genes from locus Gli-B2 were hardly expressed (e.g., less than 5% in 'Lavett') but in others they made up more than 40% (e.g., in 'Baldus').ConclusionHere, we have shown that large differences exist in relative expression levels of α-gliadins from the homoeologous Gli-2 loci among wheat genotypes. Since the homoelogous genes differ in the amount of conserved CD-epitopes, screening for differential expression from the homoeologous Gli-2 loci can be employed for the pre-selection of wheat varieties in the search for varieties with very low CD-immunogenic potential. Pyrosequencing is a method that can be employed for such a 'gene family-specific quantitative transcriptome profiling'.
Highlights
Α-gliadins form a multigene protein family encoded by multiple α-gliadin (Gli-2) genes at three genomic loci, Gli-A2, Gli-B2 and Gli-D2, respectively located on the homoeologous wheat chromosomes 6AS, 6BS, and 6DS
While T. aestivum varieties are used for bread making, tetraploid T. turgidum var. durum (AABB genome) varieties are especially suitable for pasta production
With the aim to perform an initial assessment of genetic variation in transcribed Gli-2 genes and accompanying differences in the celiac disease (CD) epitope frequency, Gli-2 transcripts from an individual plant of two hexaploid (T. aestivum) cultivars, 'Lavett' and 'Baldus', were analyzed in detail for their genomic origin (Gli-A2, Gli-B2 or Gli-D2) and for the presence of sequences encoding the CDepitopes in the 5' part of the gene
Summary
Α-gliadins form a multigene protein family encoded by multiple α-gliadin (Gli-2) genes at three genomic loci, Gli-A2, Gli-B2 and Gli-D2, respectively located on the homoeologous wheat chromosomes 6AS, 6BS, and 6DS. These proteins contain a number of important celiac disease (CD)-immunogenic domains. Products derived from wheat flour are consumed by humans in many forms such as bread, pasta and other baked foods, and wheat gluten are used as additives in sauces, soups and sweets. T. aestivum (2n = 6x = 42; AABBDD genome) is an allohexaploid that was formed through hybridization and successive chromosome doubling of three diploid Triticum/Aegilops species. The gliadins (α, β, γ and ω gliadins) and glutenins (HMW and LMW glutenins) are typical gluten components of Triticeae cereals and these protein types determine respectively the viscosity and elasticity (strength) of the dough [3,4]
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