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

全球粮食安全的基础是小麦、水稻和玉米这三种谷物，其中小麦是人类食物中植物蛋白的主要来源。在英国，这种谷物是最重要的作物，年产值约为12亿英镑。目前，英国田间小麦的平均产量为8.4吨/公顷，但这一产量依赖于高水平的矿物肥料（尤其是氮、磷和钾）和农药的使用。氮肥的使用令人关注，因为除了淡水和海洋生态系统的富营养化外，氮肥的使用还与导致气候变化的高水平能源使用和温室气体排放（如CO2、N2O）有关。然而，氮肥是实现小麦高产所必需的，通过减少氮肥投入来增加可持续性在商业上是不可行的，因为这会导致产量下降。鉴于高氮营养制度在田间是现实的，减少农药使用是提高小麦生产可持续性的一个目标。氮肥的一个不良副作用是它增加了对病原体的易感性。越来越多的证据表明，高土壤氮会促进真菌病原体的发展，如导致小麦叶斑病的Septoria （Simón et al . 2003; Loyce et al . 2008）。导致这些营养诱导的疾病发展变化的机制尚不清楚。Septoria leaf blotch （STB）是目前欧洲小麦最重要的病害，也是美国小麦经济损失最大的三大病害之一。尽管STB很重要，但关于小麦抵抗Septoria感染的防御机制或免疫反应的信息很少。杀菌剂是这一毁灭性疾病的唯一控制措施，但杀菌剂的广泛应用增加了由STB引起的全球经济成本。此外，由于目前可用的杀菌剂对新的Septoria耐药菌株的效果越来越差，STB疫情正变得越来越普遍。因此，迫切需要制定新的战略，在实地防治STB。提案中的工业合作伙伴（KWS）认识到，利用不依赖杀菌剂的内源性防御机制可能提供控制这种疾病的另一种方法，并且了解为什么氮营养水平和抗病性呈负相关可能会导致能够利用内源性防御的策略。我们的初步数据表明，一个转录因子家族（Tfs），即WRKY基因，在模型系统中已被证明是植物防御的核心，在氮素输入和田间稻瘟病抗性之间形成了联系。我们建议研究这些WRKY基因家族TFs的作用，以揭示在不同氮水平下田间对稻瘟病抗性至关重要的特定WRKY基因的身份，以及在维持产量所需的高投入生长条件下提高稻瘟病抗性的机制。该项目的总体目标是了解种植谷物的营养制度如何影响它们对STB疾病的易感性，最终目的是操纵这种关系，以便在高或最佳氮投入生长条件下保持增强的抗病性。

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.