Stacking HMW-GS transgenes in bread wheat: Combining subunit 1Dy10 gives improved mixing properties and dough functionality

Abstract

We have determined the technological properties of four lines containing combinations of three HMW-GS transgenes, encoding HMW-GS 1Ax1, 1Dx5 and 1Dy10. These lines were produced by conventional crossing of three single transgenic lines of the bread wheat cultivar Anza that contains the endogenous HMW-GS pairs 1Dx2 + 1Dy12 and 1Bx7* + 1By8 and is null for the Glu-A1 locus. Consequently, the total number of HMW-GS ranged from 4 in the control line Anza to 7 in line T618 which contains all three HMW-GS transgenes. The lines were studied over two years using a range of widely used grain and dough testing methods. All lines with transgenic subunits showed higher levels of glutenin proteins than the Anza control, and these differences were highly significant for lines T616, T617 and T618, containing, respectively, the transgenes encoding HMW-GS 1Ax1 and 1Dy10, 1Dx5 and 1Dy10 and 1Ax1, 1Dx5 and 1Dy10. These increases in glutenin levels are compensated by lower levels of gliadins present in transgenic lines. These changes affected the ratio of polymeric to monomeric gluten proteins (poly:mono), the ratio of HMW-GS to LMW-GS (HMW:LMW) and the contents of individual 1Ax, 1Bx, 1By, 1Dx and 1Dy subunits. Transgenic lines expressing subunit 1Dy10 together with x-type subunits (T616, T617 and T618) were superior to line T606, which had only increases in x-type subunits. In particular, the combination of transgenic subunits 1Dx5 and 1Dy10 (line T617) gave better dough rheological properties than the other combinations of transgenic subunits. For example, dough development time and stability were increased by 3.5-fold and 8.5-fold, respectively, while the mixing tolerance index (MTI) was decreased by 3.3-fold in line T617 with respect to the control line. Alveograph analyses showed that all four transgenic combinations had increased P values compared to the Anza control but subunit 1Dx5 greatly reduced the extensibility ( L). These results show that stacking HMW-GS transgenes by conventional crossing is a valid strategy for the improvement of wheat quality, with different effects being related to the different HMW-GS combinations.