|O'Brien, Katherine - UNIV OF ID, ABERDEEN|
Submitted to: International Gluten Workshop
Publication Type: Proceedings
Publication Acceptance Date: March 17, 2004
Publication Date: March 17, 2004
Citation: Blechl, A.E., Bregitzer, P.P., O'Brien, K., Lin, J.W., Nguyen, S.B., Anderson, O.D. 2004. Agronomic, biochemical and quality characteristics of wheats containing hmw-glutenin transgenes. Proceedings - 8th Gluten Workshop. p. 6-9. Interpretive Summary: The usefulness of wheat flours for making bread depends on the property of dough strength, which in turn depends on the amount and types of proteins in the flour. We are using a biotechnology approach to increase the amounts of one type of protein, HMW-glutenins, in wheat flour. Extra copies of natural HMW-glutenin genes are added to the wheat by genetic transformation. The transformed plants were grown in greenhouses and small quantities (a few grams) of flour made from their seeds were subjected to small-scale mixing and baking tests. In 2001, the transgenic wheats were grown outdoors in plots in a field in Aberdeen, ID. These trials yielded enough wheat seeds and flour to enable us to assess their suitability for bread-making with standard tests. The flours from the transgenic wheats with increases in HMW-glutenins made stronger doughs, compared to the untransformed control. The doughs were not only more elastic, but also tolerated long periods of mixing without breaking down. In some cases, the doughs were overly strong, and loaves baked from them were small, flat and dense. The field trial also afforded the opportunity to evaluate the growth and yield characteristics of the transgenic wheats. Most of them were similar to their non-transformed parent in these respects, but some had reduced yield and /or reduced height. These studies show that it is possible to use genetic engineering to obtain wheats with improved mixing characteristics, without changing their field performance.
Technical Abstract: Bread dough strength is primarily dependent on its composition of high-molecular-weight glutenin subunits (HMW-GS), a class of storage proteins that typically comprises 5-10% of flour proteins. We have made a set of transgenic wheats that differ both quantitatively and qualitatively in their HMW-GS compositions. All the transgenics were derived from cultivar Bobwhite, a hard white spring wheat that contains HMW-GS Ax2*, Bx7, Dx5, By9 and Dy10, and also the 1BL/1RS rye translocation. The introduced transgenes included native wheat genes for Dx5 and/or Dy10. The majority of 28 lines exhibit increases in HMW-GS levels due to additive expression of the transgenes and endogenous genes. As controls, four additional lines that contained only the transformation marker gene - bialaphos resistance controlled by the maize Ubiquitin1 promoter - were also studied. Field evaluations of these wheats grown in small replicate plots in one Idaho location in 2001 showed that many of the transgenics had reduced yield and some showed clear seed and plant morphology differences compared to their non-transformed parent. There were, however, several lines whose performance was indistinguishable from non-transformed Bobwhite. Flour was milled from these field-grown wheats and submitted to mixing and baking tests. Nearly all of the lines that contained Dx5 and/or Dy10 transgenes showed increases in polymeric protein and improved mixing tolerance compared to the controls. None of the transgenic wheats exhibited significant improvements in loaf volume. These studies show that it is possible to use biotechnology to make transgenic wheats with changes in mixing properties, without simultaneously changing agronomic characteristics.