Regulation of (1,3;1,4)-beta-glucan synthesis in the grasses

Lead Research Organisation: University of Dundee
Department Name: School of Life Sciences

Abstract

Non-cellulosic polysaccharides from cereal grain cell walls are not digested by enzymes in the human small intestine and so contribute to total dietary fibre intake, which has been shown to reduce the risk of serious human health conditions such as colorectal cancer, cardiovascular disease and type II diabetes. The effectiveness of these non-cellulosic cell wall polysaccharides, and in particular a specific class called the (1,3;1,4)-B-glucans (or B-glucans for short), in improving health outcomes is related to their levels in grain, to their fine structure and to their associated physicochemical properties. We have previously shown that barley B-glucans are synthesized by members of the CELLULOSE SYNTHASE-LIKE F and CELLULOSE SYNTHASE LIKE-H gene families (CslF and CslH). Allelic variation at individual members of these gene families (i.e. different versions of the same genes) and/or the genes that control where and when they are switched on and off and at what level, both directly or indirectly control their relative abundance and composition (e.g. molecular size) in both the grain and the rest of the plant. Indeed variation in B-glucan content is precisely what we have observed in different barley cultivars: we have shown that different varieties contain different amounts of B-glucans and that the levels observed are under both genetic and environmental control. Some 'extreme' barley varieties contain more than 30% total fibre (cf. 3.5% in brown rice, 7% in corn, 10% in oats and 12% in wheat) and have been marketed as health promoting super-foods (e.g. Sustagrain in the USA and BarleyMax in Australia). An interesting feature of these varieties is that they contain mutations in components of the starch biosynthetic pathway, suggesting a regulatory link between starch and B-glucan metabolism and accumulation. In this project we want to investigate precisely how individual members of the CELLULOSE SYNTHASE super-family, and in particular CslF and CslH gene family members, are regulated, paying particular attention to those that are switched on in the grain during grain development. The results will have important applications in barley breeding programs where low B-glucan is important for the feed, malting and distilling industries and the opposite, namely high B- glucan, is desirable in the context of human health. The likelihood of being able to exploit the knowledge we will gain about these gene families for future product development is therefore high (e.g. as a cholesterol lowering 'health superfood', as replacement thickening agents or novel food product development such as additives/replacements to wheat based flours).

Technical Summary

The overall aim of this project is to define the regulation and functional diversity of gene families that mediate the synthesis of plant cell wall polysaccharides, in particular the (1,3;1,4)-B-glucans, that are found in walls of commercially important grasses and cereals of the Poaceae. These are important because they contribute to total dietary fibre intake and have been shown to reduce the impact of serious human health conditions such as colorectal cancer, cardiovascular disease and type II diabetes. In addition, they have many potential uses in food and novel product development. (1,3;1,4)-B-Glucans are synthesised by members of the CELLULOSE SYNTHASE-LIKE (Csl) F and H subfamilies of the CELLULOSE SYNTHASE superfamily. This superfamily in rice and other cereals contains at least 46 members, with CslF genes usually numbering less than 12 and CslH genes less than four. We will use a combination of new and recently collected data to: characterise the CELLULOSE SYNTHASE super-family in cultivated barley, determine where and when each gene is expressed during barley development, examine the regulatory processes (transcriptional and post-transcriptional) that lead to variation in their abundance and activity, investigate the role of the genetic and metabolic relationships between (1,3;1,4)-B-glucan and starch synthesis, and define the genetic and enzymic determinants of (1,3;1,4)-B-glucan fine structure that affect physicochemical properties and potential end-uses. We will integrate the data in a genetic framework that will promote knowledge exchange, stimulate end-user pull and provide a mechanism for rapid exploitation by plant breeders. We will access state of the art genomics information, and employ informatics, molecular physiology, biochemistry, RNA-biology and genetics expertise in an integrated multi-disiplinary research program building on existing and highly productive interactions between large complementary groups in the UK and Australia.

Planned Impact

Who will benefit from this research?
The Triticeae cereals are a dominant component of European agriculture and barley, as a simple diploid, is a model for genomics-assisted molecular breeding. Making the assumption that understanding and being able to manipulate soluble fibre content in barley and related cereal grains will in the longer term lead to novel uses in the food and medical sectors we believe there will be an opportunity for commercial organisations that breed new varieties and the farmers that grow these new varieties in their fields to benefit from the provision of new and higher value products. While the low B-glucan malting and distilling sectors need to be maintained, they comprise only a minor use of the crop which currently is used as relatively low value animal feed. Providing the opportunity to produce a higher value commodity would increase farmers and breeders returns on investment and benefit the whole sector. SMEs focused on the extraction and use of B-glucan may ultimately emerge.

How will they benefit from this research?
Breeders will benefit from royalties paid on high value products. Farmers will benefit from being able to produce and sell a novel high value product with no additional investment, at a premium. Retailers will benefit from branding their produce 'healthy' and selling at a premium. Consumers will benefit from boosting their intake of natural fibre, offsetting the adverse social and personal impact of several serious human health conditions. The health sector could benefit from lower demand for their services and the tax payer could benefit from offsetting the costs of medical care.

What will be done to ensure that they have the opportunity to benefit from this research?
The conduit through which almost all genetic advances in crop production must pass to release their benefits to the broader community is the plant breeding / biotech sector. Translational activities from basic science to application are therefore crucial. The UK boasts one of the most efficient and successful commercial cereal breeding sectors in Europe and the PI maintains long lasting, strong and, importantly, funded collaborations with the majority of them. He has proactively engaged this community, including levy boards (farmers), maltsters, distillers, and to a ceratin extent the milling industryand will continue to do so if it is judged suitable for funding. The team of PI's have links to the academic sector and each a strong identity within the global community. A key distinguishing feature of this project is the added value through the participation of the ARC Centre of Excellence in Plant Cell Walls in Adelaide, Australia and its Director, Professor Geoff Fincher, who has many years experience in barley cell-wall structure and function. Combined, the PI's have the relevant expertise, track record and motivation to ensure the project meets a successful conclusion doing good science (on crops) along the way.

Publications

10 25 50
 
Description This grant has generated a number of publications on the genetic diversity of beta-glucan contant in barley. GWAS analyses have identified candidate genes involved in beta-glucan and arabinoxylan content.

The publications are filed by the lead PI - Prof. Robbie Waugh.

My role was to analyse alternative splicing in specific cellulose synthase genes but the involvement of alternative splicing was limited and this part of the grant completed.
Exploitation Route The findings of the project will be important in terms of nutrition and production of improved beta-glucan content.
Sectors Agriculture, Food and Drink

 
Description Collaboration on AS in beta-glucan synthesis genes 
Organisation James Hutton Institute
Country United Kingdom 
Sector Charity/Non Profit 
PI Contribution My role is small in this grant which is why I have not reported outcomes - these will be reported by the main grant holder. I have advised on gene expression analysis of genes involved in beta-glucan analyses and on possible alternative splicing. Also I have had input in developing the barley transcriptome on which some of these analyses are based.
Collaborator Contribution The partners have analysed the contribution of genes to beta-glucan production and the variation in production across different barley lines.
Impact Details reported by main grant holder.
Start Year 2014