The wheat omega-gliadin genes: structure and EST analysis.

A survey and analysis is made of all available omega-gliadin DNA sequences including omega-gliadin genes within a large genomic clone, previously reported gene sequences, and ESTs identified from the large wheat EST collection. A contiguous portion of the Gli-B3 locus is shown to contain two apparently active omega-gliadin genes, two pseudogenes, and four fragments of the 3' portion of omega-gliadin sequences. Comparison of omega-gliadin sequences allows a phylogenetic picture of their relationships and genomes of origin. Results show three groupings of omega-gliadin active gene sequences assigned to each of the three hexaploid wheat genomes, and a fourth group thus far consisting of pseudogenes assigned to the A-genome. Analysis of omega-gliadin ESTs allows reconstruction of two full-length model sequences encoding the AREL- and ARQL-type proteins from the Gli-A3 and Gli-D3 loci, respectively. There is no DNA evidence of multiple active genes from these two loci. In contrast, ESTs allow identification of at least three to four distinct active genes at the Gli-B3 locus of some cultivars. Additional results include more information on the position of cysteines in some omega-gliadin genes and discussion of problems in studying the omega-gliadin gene family.