The regulation of plant-nematode parasitism

摘要：植物线虫寄生的调控。植物寄生线虫是对全球粮食安全的持续威胁。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取食场所。植物和寄生线虫陷入了一场“进化军备竞赛”。站在第一线的是寄生虫“效应器”：在感染期间分泌到寄主植物中的分子。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的特定功能。科学界一直致力于试图理解和阻止这些效应功能。这种方法的一个弱点是，数千年来，植物一直在部署抗性基因来识别效应物，并发起免疫反应。这意味着寄生虫在强大的进化选择压力下对抗这种情况，发展了许多机制来逃避或否定效应物识别（序列多样性，快速突变的基因组区域的分割效应物，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，而且不太可能是强大的。我们需要的是一系列新的目标，这些目标还没有成为这种进化选择压力的焦点。该提案旨在通过将重点从个体效应转移到“高层”功能来提供新的目标：寄生是如何调节的？这个想法是，如果我们能破坏寄生调节的过程，我们就能同时破坏许多效应器的功能。我们对寄生调控的理解最近取得了两项突破，这表明现在是开始转移重点的合适时机。2016年，我发现了线虫效应物的调控遗传特征。这一特征将数百种不相关的效应结合在一起。这意味着有一些线虫的调节机制可以识别这一特征，并在这样做的过程中协调寄生的这一方面。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，我确定了这样一个监管机构的候选人。第二个突破是发现线虫不会同时合成所有效应器，这表明它们可能在感染期间以波的形式传递，这表明了一个复杂的“寄生程序”。效应器生产的顺序计划表明，将有一系列在特定时间点激活的附加调节器。破坏其中任何一种都可能对寄生虫严重有害。重要的是，植物免疫系统对这些主要的调节因子是“盲目的”。这意味着它们不太可能受到使靶向效应物如此困难的相同机制的保护。总之，这表明，寄生的主要监管机构将成为一组有吸引力的控制目标。在本提案中，我将识别、验证和破坏这些主监管机构。寄生线虫可预见地执行“寄生程序”的事实也让我们对它们如何转化植物组织有了一些了解。这表明寄主摄食部位形成的调控可能是一个多阶段的过程，并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，并通过线虫寄生计划将这些变化与进展联系起来，最终为理解这一现象奠定基础。

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.