Genome evolution and radical lifestyle changes in eukaryotic microbes

真核微生物的基因组进化和生活方式的彻底改变

• 批准号: RGPIN-2015-05754
• 负责人: Slamovits, Claudio
• 金额: $ 2.19万
• 依托单位: Dalhousie University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2015
• 资助国家: 加拿大
• 起止时间: 2015-01-01 至 2016-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=590618
• 关键词: Genome; evolution; radical; lifestyle; changes

Changes in evolutionary trajectories entail deep alterations in the biology of organisms, often at the level of genomic organization. A key example is genomic reduction after acquisition of an intracellular parasitic lifestyle, a phenomenon that has been investigated in bacterial endosymbionts. Eukaryotic genomes are larger and more complex than their bacterial counterparts, and the consequences of lifestyle changes on their genomes are poorly known. My research program has the long-term goal of improving our understanding of the evolution of eukaryotic genomes, with emphasis on the relationships between life history (e.g. symbiosis, parasitism) and genome form/function. To this aim, I focus my study on members of ALVEOLATA, a diverse group of eukaryotic microbes composed by apicomplexan, dinoflagellate and ciliate protozoa. This lineage is particularly well suited to investigate these questions. On one side, the apicomplexans evolved from free-living unicellular algae into highly specialized obligate intracellular parasites, some of which are very dangerous human pathogens such as the agents of malaria and toxoplasmosis. The closest relatives of apicomplexans are dinoflagellates, which collectively exhibit a bewildering array of unusual genomic features that appear to have played a major role in the evolution of these organisms. This proposal builds on our previous work advancing on our goals through the following specific topics: 1) we are exploring the genomic architecture of the dinoflagellate model species Oxyrrhis marina, whose genome is 8 times larger than human’s. Our analysis focuses on describing and analyzing genomic elements that are hypothetically involved in the size expansion and other unusual features of these genomes. We will also use biochemical and molecular biology approaches to unravel the secrets of the unique organization of their chromosomes. 2) Our second focus is on apicomplexans. So far we have been working on elucidating the relationships among the various apicomplexans lineages in order to have a solid phylogenetic framework to explore the cellular and genomic correlates of the transition from free-living and predatory organisms to highly specialized intracellular parasites. As part of this goal, we will investigate an organism called Nephromyces, whose life cycle uniquely deviates from the standard apicomplexan lifestyle: instead of growing intracellularly, Nephromyces invades a peculiar organ in their animal host where it completes its life cycle, which includes many coexisting cell types. In stark contrast to other apicomplexans, there is no evidence that it is pathogenic for its host, and some evidence points to metabolic exchanges between host and symbiont. We expect this unique microbe will shed substantial light on the origins of parasitism and its consequences.

进化轨迹的变化导致生物体生物学的深刻变化，通常是在基因组组织的水平上。一个关键的例子是在获得细胞内寄生生活方式后基因组减少，这一现象已经在细菌内共生体中进行了研究。真核生物的基因组比细菌基因组更大、更复杂，生活方式变化对它们基因组的影响鲜为人知。我的研究计划的长期目标是提高我们对真核基因组进化的理解，重点是生命史(例如共生、寄生)和基因组形式/功能之间的关系。为此，我的研究重点是ALVEOLATA的成员，这是一个由顶端复合体、甲鞭毛虫和纤毛虫原生动物组成的多样化的真核微生物群体。这种血统特别适合研究这些问题。一方面，顶端复合体从自由生活的单细胞藻类进化成高度专一的细胞内寄生虫，其中一些是非常危险的人类病原体，如疟疾和弓形虫病的病原体。顶端复合体的近亲是甲藻，它们共同展示了一系列令人眼花缭乱的不寻常的基因组特征，这些特征似乎在这些生物的进化中发挥了重要作用。这项建议建立在我们之前的工作基础上，通过以下具体主题推进我们的目标：1)我们正在探索甲藻模式物种Oxyrvis marina的基因组结构，其基因组比人类的大8倍。我们的分析重点是描述和分析与这些基因组的大小膨胀和其他不寻常特征有关的基因组元件。我们还将使用生化和分子生物学的方法来揭开它们染色体独特组织的秘密。2)我们的第二个重点是顶端复合体。到目前为止，我们一直致力于阐明不同顶端复合体谱系之间的关系，以便有一个坚实的系统发育框架，以探索从自由生活的捕食性生物向高度专业化的细胞内寄生虫转变的细胞和基因组相关性。作为这个目标的一部分，我们将研究一种名为Nephromyces的生物，它的生命周期独特地偏离了标准的复合体生活方式：Nephromyces不是在细胞内生长，而是在其动物宿主中的一个特殊器官中入侵，在那里它完成了它的生命周期，其中包括许多共存的细胞类型。与其他顶端复合体形成鲜明对比的是，没有证据表明它对宿主是致病的，一些证据表明宿主和共生体之间的代谢交换。我们预计，这种独特的微生物将为寄生虫的起源及其后果提供实质性的线索。