Tetraploid and hexaploid wheat varieties reveal large differences in expression of alpha-gliadins from homoeologous Gli-2 loci.
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'.
Salentijn
Elma Mj
EM
Plant Research International, Wageningen UR, Wageningen, the Netherlands. elma.salentijn@wur.nl
Goryunova
Svetlana V
SV
Bas
Noor
N
van der Meer
Ingrid M
IM
van den Broeck
Hetty C
HC
Bastien
Thomas
T
Gilissen
Luud J W J
LJ
Smulders
Marinus J M
MJ
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*
D000939:Epitopes; D018749:RNA, Plant; D005903:Gliadin