Detection of y-type subunit at the Glu-A1 locus in some Swedish bread wheat lines

Electrophoretic and reversed phase high performance liquid chromatographic (RP-HPLC) analyses were performed on gluten proteins extracted from flours milled from two different Swedish bread wheat lines; these lines have been reported to possess a novel high Mr, glutenin subunit controlled by a gene at the Glu-A1 locus, referred to as 21*. Although RP-HPLC indicated that subunit 21* has a surface hydrophobicity similar to that of the commonly occurring allelic subunits 1 or 2*, it differs from them in isoelectric point, being more basic when analysed by two dimensional gel electrophoresis (IEF/SDS-PAGE). RP-HPLC separations of high Mr glutenin subunits showed the presence of an additional peak, the behaviour of which was similar to that of y-type subunits encoded by genes at the Glu-Aly locus and present only in wild wheats T. urartu (AA) or T. dicoccoides (AABB). Based on chromatographic results and on the tight linkage observed with subunit 21*, it is suggested that the additional component (indicated as 21*y), present in the breeding lines analysed, corresponds to the y-type subunit encoded at the Glu-A1 locus. Genes encoding the subunits 21* and 21*y were also analysed by polymerase chain reaction (PCR). Contrary to what was observed for the polypeptide itself, the gene corresponding to subunit 21* was similar in size to that encoding subunit 2* and shorter than that corresponding to subunit 1. Moreover, the amplification product corresponding to the active 21*y gene was shorter than that of the allelic inactive gene present in the bread wheat cultivar Cheyenne. As reported for other high Mr glutenin subunits, gene size differences observed were due to a different length of the repetitive region. Because cultivated polyploid wheats have been shown to have only the x-type subunit at the Glu-A1 locus, it is speculated that the new combination, with both x- and y-type subunits expressed, might have been introgressed during breeding processes from the wild wheat progenitors T. urartu or T. dicoccoides, which have genotypes expressing both types of subunits.