The Impact of Endosymbiosis on Genome Structure and Content

内共生对基因组结构和内容的影响

• 批准号: RGPIN-2019-04042
• 负责人: Keeling, Patrick
• 金额: $ 5.03万
• 依托单位: University of British Columbia
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=714626
• 关键词: Impact; Endosymbiosis; Genome; Structure; Content

Endosymbiosis is the process where a host cell takes up and retains another cell, resulting in a long-term intracellular association. Endosymbiosis is widely accepted to have impacted evolution and cell function significantly, but we have a surprisingly superficial understanding of how the process actually works, or the ultimate fate of most endosymbionts. We study the gain or loss of endosymbionts and how partners integrate, to better explain the process and its impact on the partners. Sub-cellular organelles (mitochondria and plastids) are are the best-studied endosymbionts, but are also limited as mechanistic models by their extreme age and integration. Indeed, work on more recent insect-bacterial endosymbioses has challenged many longstanding assumptions about the process, including its mutualistic nature. Insects, however, represent a narrow spectrum of endosymbiotic diversity: protist-bacterial endosymbioses are much more diverse, but for most we have few functional or genomic insights. Using single-cell genomics to study even uncultivated microbial endosymbioses, we can develop a broader understanding of how this process unfolds, using two lines of research to balance depth and breadth: 1. Endosymbiont replacement in Euplotes. The ciliate Euplotes harbours an essential endosymbiont, Polynucleobacter, which we have shown is constantly degraded and re-established from free-living strains. But some Euplotes lack Polynucleobacter, and possess different endosymbionts, while others still have extra “accessory” endosymbionts. We will test if the dominant process of repeated replacement extends to these endosymbionts, and whether accessory endosymbionts increase functional complexity of the system. 2. Diverse systems to study protist-bacterial endosymbiosis. To examine a wide breadth of endosymbiotic contexts, we will also explore endosymbiotic integration in diverse protist hosts. One classic system is cellulose-digesting protists in termite hindguts. We will characterize bacterial endosymbionts from several recently-diverged hosts to determine how common are gains, losses, and replacements, and whether they persist through host speciation. Another system is anaerobic ciliates with hydrogen-producing relict mitochondria, “hydrogenosomes”. These can associate with methanogenic archaeal endosymbionts for hydrogen-exchange, and we find genomic reduction of hydrogenosomes may be accelerated by the presence of endosymbionts. We will test this by examining a wide range of ciliate hosts, with and without endosymbionts. Lastly, we will carry out pilot studies on under-explored systems to identify candidates for further development: free-living diplonemids with nucleus- and mitochondrion-associated endosymbionts, and a classic lab-timescale system in Amoeba. These studies will collectively provided significant insights into what are general principles in diverse stages and contexts of an important evolutionary process.

内共生是宿主细胞占据并保留另一个细胞，导致长期的细胞内结合的过程。内共生被广泛认为对进化和细胞功能产生了重大影响，但我们对这个过程是如何实际工作的，或者大多数内共生细菌的最终命运，有一个令人惊讶的肤浅的理解。我们研究内共生菌的得失以及合作伙伴如何整合，以更好地解释这一过程及其对合作伙伴的影响。 亚细胞细胞器(线粒体和叶绿体)是研究最深入的内共生体，但由于其极端的年龄和完整性，也限制了其作为机械模型的作用。事实上，最近对昆虫-细菌内共生生物的研究挑战了许多关于这一过程的长期假设，包括其互惠互利的性质。然而，昆虫代表了一种狭窄的内共生多样性：原生生物-细菌内共生要多样化得多，但对大多数人来说，我们几乎没有功能或基因组方面的见解。使用单细胞基因组学来研究未培养的微生物内共生生物，我们可以更广泛地了解这一过程是如何展开的，使用两条研究路线来平衡深度和广度： 1.放线菌中内共生菌的替代。纤毛虫Eplotes含有一种重要的内共生菌--多核细菌，我们已经证明，这种细菌不断地被降解，并从自由生活的菌株中重建。但一些游走虫缺乏多核细菌，并拥有不同的内共生体，而另一些则仍有额外的“附属”内共生体。我们将测试重复替换的主导过程是否延伸到这些内共生体，以及附属内共生体是否会增加系统的功能复杂性。 2.研究原生生物-细菌内共生作用的多种体系。为了研究广泛的内共生环境，我们还将探索不同原生生物宿主中的内共生整合。一个经典的系统是白蚁后肠中消化纤维素的原生生物。我们将对来自几个最近分离的宿主的细菌内共生体进行表征，以确定获得、损失和替换有多常见，以及它们是否在宿主物种形成过程中持续存在。另一个系统是具有产氢残留线粒体的厌氧纤毛虫，即“氢小体”。这些都可以与产甲烷的古生菌内共生菌进行氢交换，我们发现内共生菌的存在可能会加速氢小体的基因组还原。我们将通过检查具有和不具有内共生体的广泛的纤毛虫宿主来测试这一点。最后，我们将对探索不足的系统进行试点研究，以确定进一步开发的候选系统：具有核和线粒体相关内共生体的自由生活双丝体，以及阿米巴的经典实验室-时间尺度系统。 这些研究将共同为重要进化过程的不同阶段和背景下的一般原则提供重要的见解。