Molecular cloning, sequencing, and chromosome mapping of a 1A-encoded omega-type prolamin sequence from wheat

Gliadins are the most abundant component of the seed storage proteins in cereals and, in combination with glutenins, are important for the bread-making quality of wheat. They are divided into four subfamilies, the alpha-, beta-, gamma-, and omega-gliadins, depending on their electrophoresis pattern, chromosomal location, and DNA and protein structures. Using a PCR-based strategy we isolated and sequenced an omega-gliadin sequence. We also determined the chromosomal subarm location of this sequence using wheat aneuploids and deletion lines. The gene is 1858 bp long and contains a coding sequence 1248 bp in length. Like all other gliadin gene families characterized in cereals, the omega-gliadin gene described here had characteristic features including two repeated sequences 300 bp upstream of the start codon. At the DNA level, the gene had a high degree of similarity to the omega-secalin and C-hordein genes of rye and barley, but exhibited much less homology to the alpha- and beta-gliadin gene families. In terms of the deduced amino acid sequence, this gene has about 80 and 70% similarity to the omega-secalin and C-hordein genes, respectively, and possesses all the features reported for other gliadin gene families. The omega-gliadin gene has about 30 repeats of the core consensus sequences PQQPX and XQQPQQX, twice as many as other gliadin gene families. Southern blotting and PCR analysis with aneuploid and deletion lines for the short arm of chromosome 1A showed that the omega-gliadin was located on the distal 25% of the short arm of chromosome 1A. By comparison of PCR and A-PAGE profiles for deletion stocks, its genomic location must be at a different locus from gli-Ala in 'Chinese Spring'.