Deconstructing the polysaccharide matrix of the Magnaporthe oryzae wall: Deciphering the role of Gel remodelling enzymes

Two of the major global challenges for the next century will be how to ensure global food security and how to contend with emerging diseases. No pathogens are more deadly to plants than fungi - fungal diseases decimate our harvests and cause widespread malnutrition and starvation. But the burden of disease is increasing as global climate change hastens the geographic spread and the variety of plants infected. Hence, there is an immediate need to address this problem for both social and economic reasons.

Three crops, that is wheat, rice and maize, occupy some 40% of our global crop-land. Of these, rice feeds half the world's peoples, and will become yet more import as the population expands by 3 billion over the next 40 years. The rice blast fungus poses a very significant threat to rice and to global food security, given its ability to host "hop", that is, spread to new grass species. Disease can reduce the rice harvest by nearly a third, with catastrophic consequences in countries where rice is the main source of nutrition. It also acts as a model system for understanding the major cereal diseases of the UK. We need new antifungal chemistries which destroy fungal spores and so prevent spread of disease. Such chemistries must be environmentally-friendly, active at low doses and be cheap and accessible.

We will look at the processes which align and cement the polysaccharide building blocks into the framework of the fungal wall and will attempt to interfere with such activities. Nothing is known of these processes in the rice blast fungal wall, save for our recent work at Oxford. We have shown that one pivotal component of the wall framework is abundantly expressed during germination and that it adds short sugars onto and into the wall. When we remove the gene that contributes to this activity from the fungus it still grows, albeit feebly, but causes considerably less disease, and sheds some of its wall as it does so. This shed wall debris appears to trigger an early disease protection mechanism in the plant. We want to know more about this and, eventually, other components that cement other sugars onto and into the wall and alter its stiffness and whether they too boost disease immunity in the plant. Moreover, we have demonstrated that an environmentally-benign PuriCore chemistry, used to preserve supermarket salads in USA, is antifungal and that it affects wall integrity. We have shown that low doses of this chemistry prevents germination, leads to spore collapse and the shedding of wall moieties. We wish to understand better this cell wall perturbant, its impact on wall turnover and whether it causes a change in the sugar meshwork of the wall. We are uniquely placed to undertake this work with all necessary tools and technologies available to us.

Better plant protection from fungal disease demands greater insight and understanding of the dynamic nature of the pathogen wall. Our focus here is to assess the contribution of wall polysaccharide network remodelling enzymes to germling morphogenesis and pathogenicity. No inhibitors, nor indeed wall perturbant chemistries which target polysaccharide branching or crosslinking have been described to-date, perhaps because we understand so little of the mechanisms which underpin their action(s). We will attempt to redress this balance in a chemical, biological and genetic approach to study branching and elongation of glucans in Magnaporthe oryzae, armed with excellent preliminary data, novel wall perturbant chemistry and access to all tools and technologies needed.

The aim of this proposal is to focus on the glucanosyltransferase (GST) family of wall remodelling enzymes involved in glucan chain elongation and branching; to understand their role in wall remodelling, by creating gene knockout strains, assaying effects of wall perturbant chemistries on all strains and to evaluating whether wall debris shed by named mutants and / or provoked by treatment with HOCl induces innate immunity in the host plant.

The Royal Society report "Reaping the Benefits: Science and Sustainable Intensification of Global Agriculture" (2009) highlights the huge challenge of ensuring global food security over the next five decades. Crop yields must rise, but chemical inputs must fall. Novel approaches to improve productivity by protecting our crops from disease merit much attention. Our proposal aims to control disease by interfering with the polysaccharides architecture of the fungal cell wall and to invoke use of an environmentally-benign chemistry which may compromise the wall and which may also impact on plant immunity. The impact of our proposed work is therefore very significant on the world's stage with regard to Food Security but it will impact beyond plant disease, being relevant to human mycoses and emerging fungal diseases of note (eg Geomyces sp devastating bat populations and Batrachochytrium dendrobatidis decimating frogs/ toads).

This programme of research will draw together the disciplines of plant pathology, transcriptomics, wall biochemistry, antifungal action, and plant immunity under the broad umbrella of "systems biology" of the fungal wall. Despite the attractiveness of the unique fungal wall (across the Kingdoms) we know very little about the role of polysaccharide assembly.
We will attempt to redress this - our work will impact upon
i) Knowledge - giving a greater understanding of the earliest moments of fungal germination
ii) UK science - enhancing the profile of the Investigators on the national and international stage and launching the PDRA onto these stages
iii) Interdisciplinary science - endowing both Investigators and PDRA with new awareness and widened interdisciplinary skills
iv) Fostering broadened industrial links with PuriCore* in the common quest for new antifungal drug discovery in AgChem and pharmaceutical companies
v) Fuelling greater research effort across the continents.
vi) Training PDRA and PhD student in cross-disciplinary research
vii) Promoting public awareness of science and raising awareness of importance of pathogenic fungi to the plight of the hungry.

* This BBSRC IPA programme is partly funded by PuriCore. They will therefore be the most immediate industrial beneficiaries. A pre-proposal was approved by PuriCore Board of Management in early 2011 and this application authorised. The company will provide the cell wall perturbant chemistries. A Materials Transfer Agreement has been signed and the Research Contract Agreement will be in place co-incident with the start of this project. There will be regular meetings, agreed milestones and effective communication. PuriCore Executive Chairman, Chris Wightman, and Senior Scientific Director, Mark Sampson, flew in from US to join Martyn Rogers (PuriCore, UK) and SG at Oxford for discussions and preparation of the application in Feb 2011.