Analyses of alpha/beta-type gliadin genes from diploid and hexaploid wheats.

The alpha/beta-gliadin genes isolated from both hexaploid wheat (cv. Yamhill) and the diploid A genome progenitor Triticum urartu had remarkably similar sequences and differ by only a few point mutations. Primer extension analysis indicated that the transcriptional start points for individual genes in the family cluster within a few nucleotides. Comparison of the promoter region of several alpha/beta-gliadin and B-hordein genes reveals two conserved regions at about -130 and -250 bp. DNA from the hexaploid cultivars, Cheyenne and Chinese Spring, and the diploid progenitors T. urartu and Aegilops squarrosa was analysed by Southern blotting. Restriction fragment lengths of the alpha/beta-gliadin genes varied only slightly between the various wheats, although the overall copy number varied significantly. A region between approx. -1700 and -700 bp upstream from the TATA box was highly repeated in all three wheat genomes. For the hexaploid-derived gene, over 1700 bp of sequence upstream from the TATA box was determined, revealing an additional open reading frame between approx. -1550 and -1250 bp relative to the gliadin TATA box. Northern blot analysis indicated that RNA homologous to this repeated sequence family was present only in developing seed and accumulated to a maximum at late stages of maturation.