Epiphytic ecology and nutrition for control of a wheat pathogen

我的研究涉及一种真菌，小麦酵母（Zt），它攻击小麦植株，引起一种被称为小麦酵母斑疹病（STB）的疾病。STB每年给英国造成约3亿英镑的小麦产量损失和作物杀菌剂成本。更糟糕的是，这种真菌正在对可用来治疗它的杀菌剂产生耐药性。这意味着我们需要新的方法来控制感染。为了开发控制Zt的新方法，有必要充分了解真菌与小麦植物的相互作用方式，以及这种相互作用如何受到环境条件的影响。在之前的工作中，我发现Zt的一些分离株在入侵前可以在叶片表面生长10天左右。叶片表面生长的数量和持续时间在不同的真菌分离株之间是不同的，而且当同一菌株感染不同的小麦品种时也是不同的。相比之下，大多数植物病原真菌不能在叶片表面获得足够的营养以存活超过24小时。我的FLF研究计划旨在确定叶片表面生长期对Zt的重要性，它是否与疾病严重程度有关，以及分离间的真菌生长差异如何在基因组中编码。为了了解真菌在叶片表面的生存，我的项目还旨在确定真菌在此期间使用了什么营养物质，以及它如何与其他叶片表面微生物相互作用。我和我的团队目前正在描述60多个gfp标记的小麦品种的附生表型，这些小麦品种具有不同程度的抗性。我们正在将这些数据与分离株的基因型和代谢物摄取谱联系起来，以构建支撑表面生存机制的完整图景。我们已经确定了以前未描述的Zt行为，包括形成生物膜的能力。我们还进行了广泛的野外采样，并正在研究Zt与其他叶片表面微生物之间的相互作用。在项目的下一阶段，我将专注于三个目标：首先，我将创建报告菌株，以可视化不同附生表型的分离株之间营养摄取的差异。用于创建这些报告菌株的基因将基于迄今为止在项目中收集的有关附生表型的遗传和代谢差异的信息。报告者将使我们能够实时地看到不同的分离株如何对叶片表面营养可用性的变化作出反应，例如，受精或花粉沉积。我将利用这些信息提出改变杀菌剂/化肥施用制度的建议，以优化疾病控制。其次，我已经证明Zt可以形成生物膜，与非生物膜细胞相比，生物膜细胞对干燥、高温和杀菌剂等胁迫具有更大的抵抗力。我将确定生物膜是否以及何时在野外条件下形成，以及生物膜是否会改变杀菌剂处理的结果或病原体在例如热浪期间的存活。这项工作将有助于开发对天气敏感的杀菌剂制度，最大限度地提高杀菌剂的功效，从而最大限度地减少进一步出现杀菌剂耐药性的风险。第三，我将探讨我们在开发Zt生物防治工作中产生的选择。我将在我们现场收集的附生菌库中搜索与相关现场数据中疾病增加/减少相关的生物体。然后，我将进行实验，看看那些与低疾病有关的是否可以作为生物防治剂，或者相反，是否可以控制那些与疾病增加有关的，例如，通过与埃克塞特大学的公民噬菌体图书馆合作，找到感染它们的噬菌体。这三个目标将大大增加我们对Zt感染生物学和生态学的理解，以及新的疾病控制机制，然后可以与我们的农业伙伴合作进行测试。

My research concerns a fungus, Zymoseptoria tritici (Zt), which attacks wheat plants, causing a disease known as Septoria tritici blotch (STB). STB costs the UK around £300 Million per year in lost wheat yields and in the cost of the fungicide used on the crops. Worse, the fungus is developing resistance to the fungicides available to treat it. This means that we need new methods to control the infection. To develop new ways to control Zt, it is necessary to gain a full understanding of the ways in which the fungus interacts with the wheat plant, and how that interaction can be affected by environmental conditions. In previous work, I showed that some isolates of Zt can grow on the leaf surface for around ten days before invading. The amount and duration of leaf surface growth varies between fungal isolates, and also when the same isolate infects different wheat varieties. Most plant pathogenic fungi, by contrast, can't obtain enough nutrients on the leaf surface to survive for more than 24 h. My FLF research programme aimed to determine the importance of this leaf surface growth phase for Zt, whether it is related to disease severity, and how inter-isolate differences in epiphytic growth are encoded in the genome. To understand fungal survival on the leaf surface, my project also aimed to determine what nutrients the fungus is using during this period, and how it interacts with other leaf surface microbes. My team and I are currently describing the epiphytic phenotypes of over 60 GFP-tagged isolates across a panel of wheat cultivars with varying degrees of resistance. We are linking these data to the genotypes and metabolite uptake profiles of the isolates to build a complete picture of the mechanisms underpinning surface survival. We have identified previously undescribed behaviours in Zt, including the ability to form biofilms. We have also carried out extensive field sampling, and are studying the interactions between Zt and other leaf surface microbes. During the next phase of the project, I will focus on three objectives: First, I will create reporter strains to visualise differences in nutrient uptake between isolates with different epiphytic phenotypes. The genes used to create these reporter strains will be based on the information gathered in the project so far, concerning the genetic and metabolic differences underlying epiphytic phenotypes. The reporters will allow us to visualise, in real time, how different isolates respond to changes in leaf surface nutrient availability due to, for e.g., fertilisation or pollen deposition. I will use this information to propose changes in fungicide/fertiliser application regimes that will optimise disease control. Secondly, I have shown that Zt can form biofilms, which have greater resistance to stresses such as drying, high temperature, and fungicides than do non-biofilm cells. I will determine whether and when biofilm formation occurs under field conditions and whether biofilms alter the outcome of fungicide treatment or survival of the pathogen during, for example, a heatwave. This work will help to develop weather-sensitive fungicide regimes and maximise fungicide efficacy, thus minimising the risk of further fungicide resistance emerging. Thirdly, I will explore options arising from our work to develop biocontrol of Zt. I will search our field-collected epiphyte library for organisms linked to increased/decreased disease in our related field data. I will then conduct experiments to see whether those linked to low disease are viable as biocontrol agents or, conversely, whether those linked to increased disease can be controlled, for example by working with Exeter's Citizen Phage Library to find phages that infect them. These three objectives will provide significant increases in our understanding of Zt infection biology and ecology alongside novel disease control mechanisms, which can then be tested in collaboration with our agricultural partners.