Functional analysis of a symbiotic polydnavirus

许多微生物已经进化出与后生动物的联系，从有益的共生到致病。虽然细菌被公认为与后生动物形成有益的共生关系，但病毒通常被视为非生物、寄生实体，它们与宿主相互作用的方式只有利于它们自己的传播和持久性。然而，许多病毒是垂直传播的，而且与包括无脊椎动物和哺乳动物在内的各种宿主保持着持久的、非破坏性的联系。目前对病毒和宿主衍生的基因如何相互作用来调节病毒复制和维持共生关系知之甚少。携带多核糖核酸病毒的寄生蜂是病毒进化为[垂直传播的、持久的]有益共生体的最有力的例子之一。[背景研究表明，来自茧蜂的多核糖核酸病毒是从致病的核糖体进化而来的，但现在是有益的共生体，它们作为整合的前核糖体存在，但在黄蜂生命周期的非常特定的时间复制以产生病毒粒子。然而，关于多聚核糖核酸病毒和黄蜂基因如何相互作用以维持共生关系或如何调控病毒复制，人们知之甚少。为了解决这个问题，我建议将重点放在黄蜂破坏微囊虫及其相关的多聚核糖核酸病毒上，该病毒被称为破坏微囊蜂病毒(M.Droplitor BrackVirus，MdBV)。我的具体目标是：1)使用大规模平行测序技术鉴定与MdBV复制有关的基因；2)通过进行一系列功能实验来鉴定病毒粒子形成所必需的基因；以及3)鉴定病毒聚合酶结合的序列，以通过进行染色质免疫沉淀(ChIP)检测以及对捕获的DNA进行测序来评估它是否仅转录病毒基因或也转录宿主基因。我的研究的预期结果将加强对多聚核糖核酸病毒复制以及病毒和宿主基因在这一过程中所起作用的理解。[前病毒的长期持续和间歇性复制是病毒学中的一种普遍现象，对许多疾病非常重要，但对调节病毒激活的过程的了解仍然局限于少数几个病毒分类群。因此，更广泛地说，我的研究对于理解病毒和宿主基因组如何进化以形成长期关联、病毒如何进化以发挥共生体的功能以及大型DNA病毒的激活/复制如何在分子水平上进行调控至关重要。]

Many microorganisms have evolved associations with metazoans that range from beneficial symbiosis to pathogenic. While bacteria are well recognized to form beneficial symbiotic associations with metazoans, viruses are usually viewed as non-living, parasitic entities that interact with hosts in ways that only benefit their own transmission and persistence. Yet, many viruses are vertically transmitted, [and are maintained as persistent, nondestructive associations with a wide diversity of hosts, including invertebrates and mammals. Little is currently known about how virus- and host-derived genes interact to regulate viral replication and maintain the symbiotic association. Parasitoid wasps that carry polydnaviruses provide among the strongest examples of viruses evolving into [vertically transmitted, persistent,] beneficial symbionts. [Background studies show that polydnaviruses from braconid wasps evolved from pathogenic nudiviruses but are now beneficial symbionts that persist as integrated proviruses but which replicate at a very specific time in the wasp life cycle to produce virions. However, little is known about how polydnavirus and wasp genes interact to maintain the symbiotic association or how viral replication is regulated. To address this question, I propose to focus on the wasp Microplitis demolitor and its associated polydnavirus named M. demolitor bracovirus (MdBV). My specific aims are to: 1) characterize genes involved in replication of MdBV using massively parallel sequencing technology; 2) identify genes essential for virion formation by conducting a series of functional experiments, and; 3) characterize sequences the viral polymerase binds to assess whether it transcribes only viral or also host genes by conducting chromatin immunoprecipitation (ChIP) assays together with sequencing of captured DNAs. Expected outcomes of my studies will enhance understanding of polydnavirus replication and the roles of virus- and host genes play in this process. [Long term persistence as proviruses combined with episodic replication is a widespread phenomenon in virology of great importance to numerous diseases, yet understanding of the processes that regulate viral activation remain limited to a handful of viral taxa. Thus, more broadly, my study i fundamentally important for understanding how virus and host genomes evolve to form long-term associations, how viruses can evolve to function as symbionts, and how activation/replication of large DNA viruses is regulated at the molecular level.]