The objectives of this project is to determine the molecular basis for the functional properties of wheat for breadmaking and other food uses, using a combination of biophysical, biochemical and molecular genetic approaches, including the production and analysis of transgenic wheat plants.
Spectroscopic studies of whole HMW subunits and subunit peptides have provided a detailed understanding of the structures and properties of the whole subunits and their three structural domains:
1. Spectroscopic analyses of purified subunits and repetitive peptides has led to a novel theory for gluten elasticity based on inter-chain hydrogen bonding;
2. Comparisons of allelic pairs of HMW subunits associated with good and poor bread making performance have shown differences in their stability to unfolding and specific molecular interactions that may lead to impacts on gluten elasticity;
3. A new series of near-isogenic lines which differ in their number and composition of HMW subunits has been produced in the cultivar Pegaso.
Transgenic lines have been produced expressing wild type and mutant HMW subunits. Biochemical and functional studies of transgenic lines grown in replicate field trials have demonstrated that the expression of additional HMW subunits can lead to increased elasticity or to more dramatic changes in processing properties, the latter being associated with a high proportion of insoluble glutenin polymers.
The underpinning knowledge provided will facilitate the development of new types of wheat with optimised raw material quality using genetic engineering. Wheat flour consists of about 80 % starch, 10 % protein with small amounts of other components such as lipids and pentosans. Although all of these may contribute to the functional properties, the proteins appear to be particularly important in this respect. This is because proteins are the major components of gluten, which forms a network in dough and confers the crucial properties of viscosity (extensibility) and elasticity. A precise balance of these properties is required for different end uses, and this balance in turn depends on the precise composition and properties of the gluten proteins. Gluten consists of over 50 such proteins, which are classically divided into two groups which are present in approximately equal amounts. The glutenins are polymeric and form a highly viscous and elastic network which is plasticised by the monomeric gliadins. Poor processing quality of EU wheats is often related to insufficient elasticity, and the glutenin fraction has therefore been studied in most detail. This has demonstrated the importance of one particular group of proteins, called the High Molecular Weight (HMW) subunits. These proteins will therefore provide answers to three key questions :
1. What are the molecular structures of the HMW subunits ?
2. How do the structures and interactions of the HMW subunits and other gluten
proteins determine the physical (visco-elastic) and functional properties of
whole gluten ?
3. How do the HMW subunits and other gluten proteins determine the functional
properties of doughs ?
The results of these studies will allow the amino acid sequences of the individual HMW subunits to be related to their functional properties, via an understanding of their structures and molecular interactions in gluten and doughs. This will allow the use of transformation to improve the quality of wheat for breadmaking and for other food and non-food uses.
Funding SchemeCSC - Cost-sharing contracts
NR4 7UA Norwich
44316 Nantes Cedex 03
AL5 2JQ Harpenden
268 81 Svalöv
9747 AG Groningen
221 00 Lund