title: Tetraploid and hexaploid wheat varieties reveal large differences in expression of alpha-gliadins from homoeologous Gli-2 loci.
abstract: BACKGROUND
  Alpha-gliadins form a multigene protein family encoded by multiple alpha-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 alpha-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 alpha-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.
  
  
  RESULTS
  We detected large differences in relative expression levels of alpha-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').
  
  
  CONCLUSIONS
  Here, we have shown that large differences exist in relative expression levels of alpha-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'.
authors.affiliation: Plant Research International, Wageningen UR, Wageningen, the Netherlands. elma.salentijn@wur.nl
authors.forename: Elma Mj
authors.initials: EM
authors.lastname: Salentijn
authors.forename: Svetlana V
authors.initials: SV
authors.lastname: Goryunova
authors.forename: Noor
authors.initials: N
authors.lastname: Bas
authors.forename: Ingrid M
authors.initials: IM
authors.lastname: van der Meer
authors.forename: Hetty C
authors.initials: HC
authors.lastname: van den Broeck
authors.forename: Thomas
authors.initials: T
authors.lastname: Bastien
authors.forename: Luud J W J
authors.initials: LJ
authors.lastname: Gilissen
authors.forename: Marinus J M
authors.initials: MJ
authors.lastname: Smulders
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D001483:Base Sequence; D000939:Epitopes / Q000235:genetics; D020224:Expressed Sequence Tags; D018506:Gene Expression Regulation, Plant; D005787:Gene Frequency; D017343:Genes, Plant; D005838:Genotype; D005903:Gliadin / Q000235:genetics* / Q000276:immunology; D008969:Molecular Sequence Data; D011123:Polyploidy; D018749:RNA, Plant / Q000235:genetics; D017422:Sequence Analysis, DNA; D014908:Triticum / Q000235:genetics*
chemical_list: D000939:Epitopes; D018749:RNA, Plant; D005903:Gliadin