Sequence similarity between allelic Glu-B3 genes related to quality properties of durum wheat

Low-molecular-weight glutenin subunits (LMW-GSs) are wheat endosperm proteins mostly encoded by genes located at the Glu-3 loci. These proteins are of particular interest in durum wheat because a correlation between LMW-GSs encoded by genes at the Glu-B3 locus and the pasta-making quality of durum wheat semolina has been shown. We isolated and characterized two allelic lmw-gs genes located at the Glu-B3 locus and present in durum wheat lines displaying different qualitative properties. The clones pLMW1CL and lambda LMW3.1 were found to contain allelic sequences encoding LMW-GSs belonging to the good and poor quality-related groups named LMW-2 and LMW-1, respectively. The LMW-GSs specified by these genes have very large repetitive domains which are composed of repeats regularly distributed along the domain. The main difference between these two proteins is an insertion of 13 amino acids within the repetitive domain which, by itself, seems insufficient to explain the qualitative differences between LMW-2 and LMW-1. These results further support the hypothesis that the greater amount of LMW-2, rather than sequence peculiarities, accounts for the better quality observed in durum wheat cultivars possessing these subunits. The characterization of the complete primary structure of these alleles, other than providing information for an understanding of the structure-function relationship among LMW-GSs and furnishing basic material for wheat engineering, should also assist in our understanding of the evolutionary relationship between the different lmw-gs genes.