Nitrogen availability influences Septoria defence in wheat by modulating WRKY transcription factor gene expression.

Lead Research Organisation: Durham University
Department Name: Biosciences

Abstract

The foundation of global food security is built on the three cereals wheat, rice and maize, where wheat is the leading source of vegetable protein in human food. In the UK this cereal is the most important crop grown with an annual value of about £1.2 billion. The average yield of wheat in the field in the UK is currently 8.4 tonnes/ha, but this yield is dependent on high levels of mineral fertilizer (especially Nitrogen, Phosphorus and Potassium) and pesticide usage. Nitrogen (N) fertiliser use is of concern because it is associated both with high levels of energy use and greenhouse gas emissions (e.g. CO2, N2O) that cause climate change, in addition to eutrophication of fresh water and marine ecosystems. However, nitrogen fertilisation is required for achieving high yield in wheat, and increasing sustainability through decrease in nitrogen input is not commercially feasible due to the resulting fall in yield. Given that high-nitrogen nutrient regimes are reality in the field, decreasing pesticide usage is a target for enhancing sustainability of wheat production.
An undesirable side-effect of nitrogen fertilisation is that it increases susceptibility to pathogens. There is increasing evidence that high soil nitrogen enhances the development of fungal pathogens such as Septoria that causes wheat leaf blotch disease (Simón et al 2003; Loyce et al 2008). The mechanisms leading to these nutrient induced changes in disease development are not known. Septoria leaf blotch (STB) is currently the most important disease of wheat in Europe and is among the top three most economically damaging diseases of this crop in the United States. Despite the importance of STB, there is very little information available on the defence mechanisms or immune responses that allow wheat to counter Septoria infection. Fungicides provide the only control measure for this devastating disease, but extensive applications of fungicides increase the worldwide economic costs attributed to STB. In addition, STB outbreaks are becoming more prevalent as currently available fungicides are becoming less effective against new resistant strains of Septoria. Therefore there is an urgent need to develop new strategies to combat STB in the field. The industrial partners (KWS) in the proposal recognise that exploiting endogenous defence mechanisms that do not rely on fungicides may provide an alternative method to control this disease, and that an understanding of why Nitrogen nutrient level and disease resistance are inversely correlated is likely to lead to strategies which will enable exploitation of endogenous defence.
Our preliminary data have suggested that a family of transcription factors (Tfs), the WRKY genes that have been shown to be central to plant defence in model systems, form a link between nitrogen input and Septoria disease resistance in the field. We propose to investigate the roles of these WRKY gene family TFs to reveal the identity of the specific WRKYs which are critical for Septoria resistance in the field under varying nitrogen levels and mechanisms which can be exploited to boost Septoria resistance under the high input growth conditions necessary for maintaining yield.
The overall objective of this project is to gain an understanding of how the nutrient regime under which cereals are grown affects their susceptibility to STB disease, with the ultimate aim of manipulating this relationship to allow enhanced disease resistance to be retained under high or optimum nitrogen input growth conditions.

Technical Summary

Wheat yield is dependent upon the use of high levels of mineral fertilizer. This has a drastic side effect of rendering wheat plants more susceptible to diseases, particularly from the foliar pathogen Zymoseptoria tritici (Septoria), the causal agent of Septoria leaf blotch disease (STB). STB is economically the most important disease affecting yield in many wheat growing regions, including Northern Europe. Our preliminary data have suggested that a family of transcription factors (Tfs), the WRKY genes that have been shown to be central to plant defence in model systems, form a link between nitrogen input and Septoria disease in the field. We propose to investigate the roles of these WRKY gene family TFs to reveal: i) the identity of the specific WRKYs which are critical for Septoria resistance in the field under varying nitrogen levels. ii) key molecular mechanisms which will enable increased Septoria resistance under the high input growth conditions necessary for maintaining yield.
The overall objective of this project is to gain an understanding of how the nutrient regime under which cereals are grown affects their susceptibility to STB disease, with the ultimate aim of manipulating this relationship to allow enhanced disease resistance to be retained under high or optimum nitrogen input growth conditions.
Key hypotheses to be addressed in this proposal are:
1. Nitrogen availability influences the expression of WRKY transcription factors.
2. WRKY transcription factors regulate foliar disease resistance mechanisms against Septoria in wheat.
3. Manipulation of expression of WRKY transcription factors can decouple nutrient availability from Septoria susceptibility.
During the course of this project we should generate fundamentally new knowledge about the regulation of resistance mechanisms in wheat against a pathogen of major economic importance. This will allow us to develop new tools for devising new crop protection strategies against Septoria leaf botch.

Planned Impact

Loss of the UK wheat yield by Septoria is estimated between 10-30%, equating to an economic loss of £200-£600m/y. If UK publicly funded research is to underpin food security, it must deliver outputs that can be readily used by the breeding companies, as highlighted by the Royal Society report "Reaping the benefits". This project is very focused in its goal: To 'decouple' defence from growth, thereby maintaining/increasing yield with reduced susceptibility to Septoria under conventional nitrogen input through elucidating the linkages between regulators of expression (transcription factors, Tfs) and the genes they control. The proposed research is highly relevant to seed companies and cereal growers in UK agriculture, and would lead to decreased fungicide usage and lower crop losses. For the research to be translated into useful practical outcomes, a formal partnership has been developed with KWS who are the industrial partners in this LINK proposal. KWS UK Ltd, based at Thriplow, is part of the KWS Group, recognised as one of the leading cereal breeders in the world, operating in some 70 countries with a worldwide seeds turnover > 750 million Euros. KWS views higher yields, superior disease and pest resistance and improved performance in adverse conditions as key breeding objectives, reinvesting 15% of its annual turnover in breeding and research to ensure the continuing pipeline of innovative new elite cultivars with appropriate characteristics. KWS UK also has strong links with other breeders for whom they act as a route to the UK market. Both academic institutions have strong and long-standing links with KWS through previous BBSRC funding and EU funded projects (they are partners in a currently funded EU-FP7 NUE-crops project). The applicants have extensive experience of working with industry and have current collaborations with international agricultural biotechnology companies (Lonza, Monsanto, Tozer Seeds, Syngenta), and have had previous BBSRC-funded LINK projects (Susceptibility of the cereal aphid Metopolophium dirhodum to the entomopathogenic fungus Pandora neoaphidis on GNA wheat; PI, Rothamsted_Res; Co-I, AMRG) and DEFRA-funded LINK projects (Insecticidal fusion proteins; PI, JAG). The proposed collaboration with KWS will provide a route for the practical uptake of the technologies developed by this project.

This project seeks to interface with the seeds and cereal breeding company KWS so that high yielding wheat lines exhibiting resistance to Septoria can be selected for using markers derived from genes identified within the project, enabling basic crop science research to be translated into practical applications by breeders. Information gained from this project will give greater flexibility to wheat breeders to enable them to respond to EU driven change (e.g. 'reducing the use of plant protection products') and in so doing, will increase UK competitiveness by allowing it to respond more effectively to increased demands for world food and to climate change.

Development of novel scientific bases for the protection of wheat from pathogen attack, as proposed in this research, has the potential to generate patentable know-how and products. Input and advice relating to any Intellectual Property issues that may arise during the project will be sought from patent and IP specialists in Durham University Newcastle University and KWS.

Dissemination is viewed as key to impact. Where appropriate, information will be disseminated through peer-reviewed journals, presentations at national and international conferences, the trade press, and through the media (radio, TV, internet). Agricultural shows such as Cereals, will be a target for dissemination. These routes for dissemination will bring the salient findings of this project to all interested parties. Collaboration with KWS will ensure rapid technology transfer to the industry and facilitate effective commercialisation.
 
Description Zymoseptoria Tritici (also known commonly as Septoria) is the causal pathogen of Septoria Tritici Blotch (STB), one of the most damaging wheat foliar diseases across temperate regions, causing up to 40% yield loss if fungicides are not deployed. Resistance to Septoria is one of the major targets in wheat breeding programmes. Understanding the molecular mechanisms that underpin Septoria-wheat interaction will be crucial for generating new control strategies against STB. Our report provides new insight into Septoria- wheat interaction and also details an approach that could pave the way to boosting immunity in wheat under field conditions against this devastating pathogen.
Plant hormones are essential regulators of growth and immunity. Jasmonic acid (JA) is an ubiquitous plant hormone whose abundance determines how programmed developmental events are adapted to wounding, pest and pathogen attack. JA-dependent defence has been widely studied in the model system Arabidopsis thaliana but its role in immunity in wheat is largely unknown. In this study we provide a new facet to JA signalling in wheat that has not been described in other model plants. Jasmonic acid (JA) plays a central role during defence against necrotrophic pathogens. Recently transcriptomic studies established that JA biosynthetic genes are upregulated upon Septoria infection. Nevertheless the mechanism underpinning the signal perception and transduction remains yet unclear. Here we reveal that TaWRKY10 gene controls a novel regulatory step in JA responses in wheat.
Exploitation Route In this study we identify a WRKY transcripton factor, TaWRKY10 as a grass subfamily Pooideae-specific component of resistance to a globally important wheat disease Septoria leaf blotch (STB). TaWRKY10 gene expression correlated with eight wheat varieties with distinct susceptibilities to Septoria under field conditions. Using gene-silencing experiments we demonstrate the different degrees of susceptibilities to Septoria is due to the expression levels of TaWKRY10. Transcriptional profiling of TaWRKY10 knock-down plants indicates that it is a negative regulator of the JA receptor TaCOI1 gene expression. Wheat plants silenced for TaWRKY10 show an upregulated JA response. We demonstrate that TaWRKY10 downregulates JA responses contributing to Septoria susceptibility observed in wheat varieties. Our data indicates that manipulating TaWRKY10 may provide a new pathway to regulating JA signaling in plants and potentially increasing Septoria resistance in wheat.
This can be done in conjunction with industry partners or with government funding.
Sectors Agriculture, Food and Drink

 
Description The industry partner in currently evaluating the efficacy of using the data generated within the project to develop new wheat varieties with increased resistance against fungal diseases. A world patent for the new technology has been granted.
First Year Of Impact 2018
Sector Agriculture, Food and Drink
Impact Types Economic

 
Description KWS technicians funding
Amount £160,000 (GBP)
Funding ID BB/M022048/1 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 09/2018 
End 10/2018
 
Title transgenomic complementation assays 
Description Expressing gnes from unrelated plant species to identify conserved signalling pathways 
Type Of Material Technology assay or reagent 
Year Produced 2006 
Provided To Others? Yes  
Impact Publications form the reagents generated from this method 
 
Description nutrient effect on Septoria resistance in wheat 
Organisation Newcastle University
Department School of Biology
Country United Kingdom 
Sector Academic/University 
PI Contribution Generated new molecular tools for the development of control strategies against septoria tritici blotch disease in wheat
Collaborator Contribution Knowledge of nutrient use efficiency in wheat
Impact Publications; Lee et al., 2015 New Phytologist BBSRC grant BB/M022048/1 Industrial funding form KWS breeding company Patents filed on the discoveris from the work
Start Year 2012
 
Description media presentation 
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 Media (as a channel to the public)
Results and Impact short interview on Farming today program on BBC radio 4
Year(s) Of Engagement Activity 2015