The molecular and genetic basis of aphid virulence

这个项目旨在促进我们对参与蚜虫与寄主植物之间分子相互作用的基因的理解。这一点很重要，因为在危害粮食和非粮食作物的全球害虫排行榜上，蚜虫位居榜首，每年造成数亿美元的损失。除了吸取汁液外，它们还是病毒的主要传播者，因此需要大量使用昂贵的杀虫剂。根据欧盟立法，这些化学品中的一些将被撤回，另一些由于蚜虫产生抗药性而不再有效，这进一步加剧了开发新的强大但可持续的作物保护途径的紧迫性。我们提出的路线以遗传学为中心，而不是化学物质。大多数蚜虫物种都有一定范围的寄主植物，它们可以成功地以这些寄主植物为食。在这些蚜虫-寄主物种对中，两边的一些遗传变异可以极大地影响结果：蚜虫的成功被称为毒力，而成功的植物防御被称为抗性。虽然一些对蚜虫的特定抗性很可能是以类似于更广为人知的抗病机制的“基因对基因”的方式运作，但我们还不清楚蚜虫毒力蛋白(统称为效应器)与植物抗性蛋白之间相互作用的细节。这种知识差距阻碍了作物遗传改良的进展。由于豌豆蚜虫(Acyrthosiphon Pisum)及其寄主之一Barrel Medicc(Medicago Truncatula)的基因测序技术和基因组数据库的巨大进步，首次有机会研究这两个物种的基因，以此作为确定谁应为蚜虫的成功或寄主的抗性负责的途径。我们最近的工作产生了重要的知识和资源，使拟议的项目可行。首先，我们用强毒和非强毒亲本进行杂交，获得了一系列新型的蚜虫杂交种。这些杂交种中有几个表现出亲本中没有的毒力模式，这表明毒力基因存在复杂的遗传模式。其次，我们的初步研究表明，在致病和非致病的蚜虫之间，基因表达模式和蛋白质谱有很大的差异。综上所述，这些发现为缩小影响因素的范围提供了一条有效的途径，并极大地帮助我们了解对蚜虫的抗性是如何发挥作用的。我们的目标是确定决定蚜虫成功或寄主抗性的主要基因。这样的知识可能会导致在广泛的农作物中产生持久抗性的新途径。我们将测试在豌豆蚜虫-医学系统中发现的机制与其他主要英国害虫的关系有多密切，如桃-土豆蚜虫(Myzus Persicae)，它攻击非常广泛的作物，对其几乎或根本没有抗药性。该项目有四个主要活动。首先，我们将产生更多毒性不同的杂交蚜虫种群。这些蚜虫集合将使我们能够发现多种致病和非致病的蚜虫之间的主要共同差异。我们将测量以RNA和蛋白质形式表达的基因产物的数量，并同时寻找可能影响蛋白质功能的DNA序列变异。其次，我们将测试最重要的候选基因和蛋白质，将它们插入到医学植物中，看看它们是否专门模仿寄主侵染症状和/或影响蚜虫的毒力。第三，我们将通过描述一种对某些豌豆蚜虫类型具有特别强抗性的Medc基因来了解更多关于寄主抗性的过程。最后，我们将比较豌豆蚜效应物与其在桃-土豆蚜虫中的等价物，并将测试插入寄主植物中的豌豆蚜效应物是否有可能影响对其他物种的抗性，特别是桃蚜-土豆蚜虫。

This project aims to advance our understanding of the genes involved in molecular interactions between aphids and their host plants. This is important because aphids are at the top of the global league table of insect pests that damage food and non-food crops, causing losses of hundreds of millions of dollars every single year. In addition to sucking sap, they are major transmitters of viruses, and necessitate extensive use of costly pesticides. Some of these chemicals will be withdrawn under EU legislation and others are no longer effective due to aphids becoming resistant, adding further urgency to develop new robust but sustainable routes to crop protection. The route we propose centres on genetics rather than chemicals. Most aphid species have a defined range of host plants on which they can successfully feed. Within those aphid-host species pairs, some genetic variants on both sides can dramatically affect the outcome: aphid success is known as virulence, and successful plant defence is known as resistance. Although some specific resistance to aphids most likely operates in a "gene-for-gene" manner similar to better known mechanisms acting against diseases, we do not yet understand the details of the interactions between the aphid virulence proteins, collectively known as effectors, and plant resistance proteins. This knowledge gap hampers progress toward crop genetic improvement. Because of huge advances in gene sequencing technologies and genomic databases for both pea aphid (Acyrthosiphon pisum) and one of its hosts, barrel medic (Medicago truncatula), there is for the first time the opportunity to study genes in both species as a route to defining those responsible for success of the aphid or resistance of the host.Our recent work has generated vital knowledge and resources that make the proposed project feasible. First, we have made a series of novel aphid hybrids by mating virulent and non-virulent parents. Several of these hybrids exhibited virulence patterns not seen in either parent, which suggests that there are complex patterns of inheritance of virulence genes. Second, our pilot studies show that there are major differences between gene expression patterns and protein profiles between virulent and non-virulent aphids. Together, these findings enable an efficient route to narrow down the effectors responsible, and can greatly aid our understanding of how resistance to aphids works. Our aim is to define the major genes that determine aphid success or host resistance. Such knowledge can potentially lead to new routes to generating durable resistance in a wide array of crop plants. We will test how closely the mechanisms uncovered in the pea aphid-medic system are also relevant to other major UK pests such as peach-potato aphid (Myzus persicae), which attacks a very wide range of crops and for which little or no resistance is known.The project has four major activities. First, we will generate further hybrid aphid populations that differ in virulence. These aphid sets will allow us to discover the major common differences across multiple virulent and non-virulent aphids. We will measure amounts of expressed gene products, both as RNA and as protein, and simultaneously look across the entire pea aphid genome for DNA sequence variants that may affect protein function. Second, we will test the top candidate genes and proteins by inserting them into medic plants to see if they specifically mimic host infestation symptoms and/or affect aphid virulence. Third, we will learn more about host resistance processes by characterising a medic gene that gives particularly strong resistance to some pea aphid types. Finally, we will compare pea aphid effectors with the their equivalents in peach-potato aphid, and will test whether pea aphid effectors inserted into host plants have the potential to affect resistance to other species, especially peach-potato aphid.