The regulation of plant-nematode parasitism

植物寄生线虫是全球粮食安全的一个持续威胁。经济上最重要的物种有能力将植物细胞转化为永久和专用的摄食场所。植物和寄生线虫陷入了一场“进化军备竞赛”。在第一线，是寄生虫的“效应器”：在感染过程中分泌到宿主植物中的分子。植物寄生线虫使用数百种效应器来操纵它们的宿主。通常，单个效应器针对宿主中的特定功能。科学界一直致力于了解和阻断这些效应子功能。这种方法的一个弱点是，数千年来，植物一直在利用抗性基因来识别效应子，并产生免疫反应。这意味着寄生虫在强大的进化选择压力下对抗这一点，发展了许多机制来逃避或否定效应子识别（序列多样性，在基因组快速突变的区域中分配效应子，功能冗余等）。实际上，这意味着针对单个效应器来控制寄生虫很少是非常成功的，并且不太可能是稳健的。我们需要的是一系列新的靶点，这些靶点并不是这种进化选择压力的焦点，这个提议旨在通过将焦点从单个效应器转移到“高级”功能来提供新的靶点：寄生是如何调节的？这个想法是，如果我们能够破坏寄生调节的过程，我们就可以同时破坏许多效应器的功能。我们对寄生调节的理解最近取得了两项突破，这表明现在是启动这种焦点转移的正确时机。这个特征统一了数百个原本不相关的效应器。这意味着有一些线虫的调节机制，承认这一签名，并在这样做编排这方面的寄生。我预测，如果我们能够破坏这个“主调节器”，它将反过来破坏数百个相关的效应器。在最近的一次努力中，我已经确定了这种调节剂的候选者。第二个突破是发现线虫不会同时合成所有的效应物，这表明它们可能是以波的形式传递的，这表明在感染过程中有一个复杂的“寄生程序”。这种效应物产生的顺序程序表明，将有一系列在特定时间点被激活的额外调节器。破坏其中任何一个都可能对寄生虫造成严重损害。重要的是，植物免疫系统对这些主调节器是“盲”的。这意味着它们不太可能受到使靶向效应器如此困难的相同机制的保护。总之，这表明寄生主调节器将是一组有吸引力的控制目标。在这个提议中，我将识别、验证和破坏这些主调节器。寄生线虫可预见地执行“寄生程序”的事实也给了我们一些关于它们如何转化植物组织的见解。这表明寄主取食部位形成的调节可能是一个多阶段的过程，且具有相同或非常相似的阶段数。这是对这种组织如何形成的新见解，并提供了一个了解支撑这一过程的基本生物学的机会。在本提案中，我将开发一个系统来测量宿主基因调控的变化，并将这些变化与线虫寄生程序的进展联系起来，最终建立理解这种现象的基础。

Summary: The regulation of plant-nematode parasitism.Plant-parasitic nematodes are a persistent threat to global food security. The most economically important species have the ability to transform plant cells into permanent and dedicated feeding sites. Plants and parasitic nematodes are locked in an "evolutionary arms race". At the front-line, are the parasite "effectors": molecules secreted into the host plant during infection. Plant-parasitic nematodes use hundreds of effectors to manipulate their host. Often individual effectors target a specific function in the host. The scientific community has focused on trying to understand and block these effector functions.A vulnerability of this approach is that for thousands of years plants have been deploying resistance genes to recognise effectors, and mount an immune response. This means that the parasites are under a strong evolutionary selection pressure to counteract this, developing a number of mechanisms to evade or negate effector recognition (sequence diversity, partitioning effectors in regions of the genome that mutate rapidly, functional redundancy, etc.). Practically, this means that targeting individual effectors to control the parasite is rarely highly successful, and unlikely to be robust. What we need is a series of new targets that have not been the focus of this kind of evolutionary selection pressure.This proposal is designed to deliver new targets by shifting the focus away from individual effectors to "high-level" functions: how is parasitism regulated? The idea is that if we can disrupt the process of parasitism regulation we can disrupt the functions of many effectors at the same time. Two recent breakthroughs in our understanding of parasitism regulation suggest that now is the right time to initiate this shift in focus.In 2016 I identified a regulatory genetic signature of nematode effectors. This signature unifies hundreds of otherwise unrelated effectors. This implies there is some nematode regulatory machinery that recognises this signature, and in so doing orchestrates this aspect of parasitism. I predict that if we could disrupt this "master-regulator", it would in turn disrupt hundreds of associated effectors. In a recent effort I have identified a candidate for such a regulator.The second breakthrough is the discovery that nematodes do not synthesise all effectors at the same time, suggesting that they may be delivered in waves that indicate a complex "parasitism programme" during infection. This sequential programme of effector production suggests that there will be a series of additional regulators that are activated at specific time-points. Disrupting any of these is likely to be severely detrimental to the parasite. Importantly, the plant immune system is "blind" to these master regulators. This means that they are unlikely to be protected by the same mechanisms that make targeting effectors so difficult. Together, this suggests that parasitism master regulators will be an attractive set of targets for control. In this proposal I will identify, validate, and disrupt these master-regulators.The fact that parasitic nematodes predictably execute a "parasitism programme" also gives us some insights into how they transform plant tissues. It suggests that the regulation of feeding site formation in the host is probably a multi stage process, and has the same or a very similar number of stages. This is a new insight into how this tissue is formed and presents an opportunity to understand the fundamental biology that underpins this process. In this proposal I will develop a system to measure changes in the host gene regulation and link these changes to progression through the nematode parasitism programme, ultimately building the foundation to understand this phenomenon.