| Summary: | <p>Abstract</p> <p>Background</p> <p>High molecular weight glutenin subunits (HMW-GSs), encoded by the genes at <it>Glu-1</it> loci in wheat and its related species, are significant in the determination of grain processing quality. However, the diversity and variations of HMW-GSs are relatively low in bread wheat. More interests are now focused on wheat wild relatives in Triticeae. The genus <it>Aegilops</it> represents an important germplasm for novel HWM-GSs and other useful genes for wheat genetic improvement.</p> <p>Results</p> <p>Six novel <it>Glu-1</it> alleles and HMW-GSs were identified and characterized from three species of <it>Aegilops</it> section <it>Sitopsis</it> (S genome). Both open reading frames (ORFs) and promoter regions of these <it>Glu-1</it> alleles were sequenced and characterized. The ORFs of <it>Sitopsis Glu-1</it> genes are approximately 2.9 kb and 2.3 kb for x-type and y-type subunits, respectively. Although the primary structures of <it>Sitopsis</it> HMW-GSs are similar to those of previously reported ones, all six x-type or y-type subunits have the large fragment insertions. Our comparative analyses of the deduced amino acid sequences verified that <it>Aegilops</it> section <it>Sitopsis</it> species encode novel HMW-GSs with their molecular weights larger than almost all other known HMW-GSs. The <it>Glu-1</it> promoter sequences share the high homology among S genome. Our phylogenetic analyses by both network and NJ tree indicated that there is a close phylogenetic evolutionary relationship of x-type and y-type subunit between S and D genome.</p> <p>Conclusions</p> <p>The large molecular weight of HMW-GSs from S genome is a unique feature identified in this study. Such large subunits are resulted from the duplications of repetitive domains in <it>Sitopsis</it> HMW-GSs. The unequal crossover events are the most likely mechanism of variations in glutenin subunits. The S genome-encoded subunits, 1Dx2.2 and 1Dx2.2* have independent origins, although they share similar evolutionary mechanism. As HMW-GSs play a key role in wheat baking quality, these large <it>Sitopsis</it> glutenin subunits can be used as special genetic resources for wheat quality improvement.</p>
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