Manipulation of cell wall synthesis to improve the dietary fibre composition of wheat flour

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We intend to identify the genes and enzymes responsible for catalysing the synthesis of arabinoxylan (AX), focusing on xylan synthase, xylan arabinosyl transferase and xylan feruloyl transferase. We will use this knowledge to develop new wheat genotypes with enhanced soluble fibre composition of flour to improve its nutritional properties. The project can be divided into four parts: (1) Functional characterisation of candidate genes encoding enzymes of AX synthesis: genes which are predicted to encode enzymes for grass-specific steps will be expressed in Arabidopsis. The secondary cell walls of transformed lines will be analysed for the novel structrual features which would demonstrate gain-of-function using highly sensitive techniques (MS, PACE and GC-MS). In a second approach, insect cells will be transformed to express the enzymes. Secreted proteins will be used for in vitro assays using labelled acceptor or donor molecules and product detection by a combination of HPLC, PACE, MS techniques. (2) Demonstration of predicted effects of changes in gene expression on wheat dietary fibre: transgenic wheat lines will be generated which over-express putative arabinosyl transferase genes and have RNAi-induced decreased expression of feruloyl transferase and xylan synthase genes. Seed of these lines will be tested for the predicted increase in soluble AX in endosperm cells. (3) Identification of knock-down mutants of feruloyl transferase in a wheat TILLING population. Again the seed of these lines will be tested for increase in soluble AX. If successful, these lines will provide a non-GM route to increase dietary fibre content of wheat flour. (4) Map the characterized genes in hexaploid wheat using doubled-haploid populations and relate the loci to QTLs for soluble fibre content and composition. This will assist breeders to introduce beneficial alleles of these genes into commercial varieties.

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