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

Lead Research Organisation: University of Cambridge
Department Name: Biochemistry

Abstract

Manipulation of cell wall synthesis to improve the dietary fibre composition of wheat flour: Summary Wheat white flour products play a huge role in the human diet. The manifold health benefits of fibre in foods are now well established, but the useful fibre content of wheat flour is low compared to oats and barley. This is because the major wheat flour fibre component, arabinoxylan (AX) from the endosperm cell walls, is typically only 25% soluble and it is believed to be soluble fibre that confers the most health benefits. Thus increasing the soluble fibre content of wheat flour is a major target for public health improvement. The solubility of AX is determined by its structure; greater substitution of the xylan backbone by arabinose increases solubility, but cross-linked ferulic acids attached to these arabinose units decrease solubility. We recently identified candidate genes responsible for all the key steps in the synthesis of AX including the addition of arabinose residues and feruloylation using a novel bioinformatics approach. We have now augmented this with analysis of transcriptome data from developing wheat grain. This in general supports our published analysis (but has caused us to revise our view on the best candidate genes encoding arabinosyl transferases) so that we have strong candidates genes for these key steps which determine the solubility of AX. The proposed research is designed (1) to provide unequivocal evidence of the function of the enzymes (2) to demonstrate that manipulation of the encoding genes in transgenic wheat has the predicted effect on the amount of soluble AX in endosperm cell walls (3) to identify changed forms of the candidate genes in a mutant wheat population which are also predicted to increase the solubility of AX. The plants carrying this form of the genes are non-GM so can be used to develop commercial wheat varieties with increased soluble fibre (4) to map the genes so that molecular markers can be found for any wheat populations which show variation in these genes. This allows wheat breeders to rapidly incorporate any beneficial versions of the genes which exist naturally in populations into commercial varieties.

Technical Summary

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.

Publications

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Anders N (2012) Glycosyl transferases in family 61 mediate arabinofuranosyl transfer onto xylan in grasses. in Proceedings of the National Academy of Sciences of the United States of America

 
Description We have discovered a family of genes called GT61 that could help us breed grasses with improved properties for diet and bioenergy. The genes are important in the development of the fibrous, woody parts of grasses, like rice and wheat, by decorating cell wall xylan with arabinose, thus changing the properties of the plant fibres. We hope that by understanding how these genes work, we might for example be able to breed varieties of cereals where the fibrous parts of the plants confer dietary benefits or crops whose straw requires less energy-intensive processing in order to produce biofuels.
Exploitation Route Links to plant breeding companies to make improved wheat. GM or breeding of improved grasses for bioenergy and forage crops.
Sectors Agriculture, Food and Drink

 
Description The work is being used to find plants that have improved properties for animal feed and bioenergy, and by academic researchers.
First Year Of Impact 2011
Sector Agriculture, Food and Drink
Impact Types Societal,Economic

 
Description BBSRC Synthetic biology centre
Amount £12,000,000 (GBP)
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 07/2014 
End 06/2019
 
Description ISIS
Amount £2,600 (GBP)
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 04/2009 
End 03/2010
 
Description Tsinghua-Cambridge-MUT LCEUA
Amount $200,000 (USD)
Organisation Government of China 
Sector Public
Country China
Start 10/2010 
End 09/2016
 
Description BBSRC business article 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Published in BBSRC Business April 2012

no actual impacts realised to date
Year(s) Of Engagement Activity 2012
 
Description BBSRC press release 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Participants in your research or patient groups
Results and Impact BBSRC press release

no actual impacts realised to date
Year(s) Of Engagement Activity 2012
 
Description Cambridge Science Fair 2010 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach regional
Primary Audience Public/other audiences
Results and Impact Science week event, BBSRC stand Bioenergy display

no actual impacts realised to date
Year(s) Of Engagement Activity 2010
 
Description Cambridge Science fair 2011 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Demonstration of bioenergy to public. One day event. Contribution to BBSRC bioenergy outreach pack.

no actual impacts realised to date
Year(s) Of Engagement Activity 2011