Functional Genomics of Aphid Adaptation to Plant Species

1.背景：桃蚜Myzus persicae(GPA)是一种世界性的重要农艺害虫，可寄生在50多个植物科的400多种不同植物上，具有世界纪录的抗药性机制，对至少70种不同的合成化合物表现出抗性。此外，GPA具有显著的可塑性，因此由基因相同的雌性组成的克隆人可以在广泛的植物物种上存活和繁殖。这与大多数其他种类的蚜虫形成了鲜明的对比，包括豌豆蚜虫(Acyrthosiphon Pisum)，它已经适应了一个植物科中的一个或几个相关植物物种。大问题：GPA表型可塑性背后的遗传控制机制是什么？这种可塑性是否与GPA在过去60年中对至少70种不同合成化合物的抗药性进化能力有关？3.假设：我们假设GPA的表型可塑性是由于它(1)以某些对毒力重要的多基因家族的扩大的形式进行基因组适应，以及(2)表观遗传调节影响基因家族成员的基因表达水平。根据对植物寄主和杀虫剂的暴露，基因家族中的某些成员受到不同程度的上调或下调，为寄生虫提供了一个多功能的“遗传工具箱”。支持数据：霍根豪特实验室已经为GPA克隆“O”开发了研究工具，这种克隆在英国占主导地位，近年来对多种作物造成了损害。我们坚持认为这个克隆是遗传上相同的雌性，可以在不同的植物物种上生存和繁殖，例如大白菜和烟草植物，这些植物产生不同的防御化合物，对蚜虫有毒。GPA克隆O的全基因组序列目前正在组装，并使用基因表达数据进行注释。我们有证据表明，特定基因家族的成员，如组织蛋白和角质蛋白，在GPA对植物物种的表型适应中发挥作用。我们还对细胞色素450单加氧酶(P450)感兴趣，它是植物化学物质和杀虫剂等有机物的解毒酶。最后，我们开发了植物介导的RNA干扰(RNAi)技术，使研究特定GPA基因的敲除对不同植物物种GPA生存和繁殖的影响成为可能。目的：在第一个目标中，我们将推进物理基因组图谱的构建，确定编码序列，并对GPA克隆O的基因家族成员进行进化分析。在第二个目标中，我们将评估在不同植物上饲养并暴露于各种农药下的GPA克隆O中哪些基因存在差异调控。我们还将对其他对杀虫剂敏感和抗药性的GPA克隆的基因组进行测序，并确定差异表达的基因是否受到高突变频率的影响。在第三个目标中，我们使用植物介导的RNAi来下调特定基因的表达，以评估它们对GPA在不同植物物种上和在杀虫剂暴露下生存能力的影响。我们将评估DNA甲基化是否与GPA表型可塑性有关。6.影响：在这个项目完成后，我们将更好地了解GPA如何适应多种植物物种，以及这是否与GPA的抗药性发展机制有关。我们还将阐明对杀虫剂敏感和抗药性的GPA克隆之间的基因组变异水平。这项研究对我们全面了解昆虫如何适应环境至关重要。最终，这可能会对作物病虫害防治中日益严重的抗药性进化问题产生实际影响。

1. The Background: The green peach aphid (GPA) Myzus persicae, an agronomically important pest worldwide, can colonize over 400 different plant species from more than 50 plant families and holds the world record of insecticide resistance mechanisms, showing resistance to at least 70 different synthetic compounds. Moreover, GPA is remarkably plastic such that one clone consisting of genetically identical females can survive and reproduce on a wide range of plant species. This is in contrast to majority of other aphid species, including the pea aphid (Acyrthosiphon pisum), which has adapted to one or a few related plant species within one plant family.2. The Big Questions: What are the genetic control mechanisms that underlie the phenotypic plasticity of GPA? Is this plasticity related to GPA ability to evolve insecticide resistance to at least 70 different synthetic compounds in the last 60 years, i.e. an "evolutionary blink-of-an-eye"?3. The Hypotheses: We hypothesize that the phenotypic plasticity of GPA is due to its (1) genomic adaptations in the form of the expansion of certain multigene families that are important for virulence, in combination with (2) epigenetic regulation affecting gene expression levels of gene family members. Depending on exposure to plant hosts and pesticides, certain members within gene families are differentially up or down-regulated, providing the parasite with a versatile "genetic toolbox".4. The Supportive Data: The Hogenhout lab has developed research tools for GPA clone "O", which has predominated in the UK, causing damage to diverse crops in recent years. We maintain this clone as genetically identical females that can survive and reproduce on diverse plant species, including for example Chinese cabbage and tobacco plants, which produce different defense compounds that are toxic to aphids. The GPA clone O whole genome sequence is currently being assembled and annotated using gene expression data. We have evidence that members of specific gene families, such as cathepsins and cuticular proteins, play a role in the phenotypic adaptation of GPA to plant species. We are also interested in cytochrome 450 monooxygenases (P450s), which are detoxification enzymes of organic substances such as phytochemicals and pesticides. Finally, we have developed the plant-mediated RNA interference (RNAi) technology enabling studies of the effect of the knock down of specific GPA genes on GPA survival and reproduction on various plant species.5. The Objectives:In the first objective we will advance the construction of a physical genomic map, identify coding sequences and conduct evolutionary analysis of gene family members of GPA clone O. In the second objective we will assess which genes are differentially regulated in GPA clone O reared on different plant species and exposed to various pesticides. We will also sequence the genomes of additional GPA clones that are susceptible and resistant to pesticides and determine if differentially expressed genes are subject to high mutation frequencies. In the third objective we use plant-mediated RNAi to knock down the expression of specific genes to assess their effect on the ability of GPA to survive on different plant species and upon insecticide exposure. We will assess if DNA methylation is involved in GPA phenotypic plasticity. 6. The Implications: At completion of this project we will have gained a better understanding of how GPA adapts to multiple plant species and if this relates to mechanisms involved in the development of insecticide resistance of GPA. We will also have elucidated the level of genomic variation amongst GPA clones susceptible and resistant to pesticides. This research is fundamentally important to our overall understanding of how insect adapt to their environments. Ultimately, this could have practical implications for the increasing problem of the evolution of insecticide resistance in crop-pest control.