Knowledge of the origin of eukaryotes is key to broadening our understanding of the eukaryotic genome and the relationship among internal structures within a eukaryotic cell. Since the discovery of archaea in 1977 and the proposal of three-domain tree of life by the American microbiologist Carl Woese, the intimate relationship in evolution between eukaryotes and archaea has been demonstrated by considerable experiments and analyses. From the beginning of the 21st century, with the development of phylogenetic methods and the discovery of new archaeal phyla more related to eukaryotes, increasing evidence has shown that Eukarya and Archaea should be merged into one domain, leading to a two-domain tree of life. Nowadays, the Asgard superphylum discovered via metagenomic analysis is regarded as the closest prokaryotes to eukaryotes. Nevertheless, several key questions are still under debate, such as what the ancestors of the eukaryotes were and when mitochondria emerged. Here, we review the current research progress regarding the changes of the tree of life and the detailed eukaryotic evolutionary mechanism. We show that the recent findings have greatly improved our knowledge on the origin of eukaryotes, which will pave the way for future studies.
作为重大进化谜题,真核生物起源的研究对于解码真核基因组、阐释真核细胞内部结构之间的关系有重要启示作用。在1977年美国微生物学家Carl Woese发现古细菌并提出三域生命之树之后,大量研究显示古细菌与真核生物在进化上存在着密切联系。21世纪以来,系统发育分析方法不断改进,泉古菌门(Crenarchaeota)、广古菌门(Euryarchaeota)之外与真核生物更加相似的新古细菌门类也相继被发现,这些证据更加支持将真核生物与古细菌合并为一域,形成二域生命之树。目前,通过宏基因组技术发现的Asgard古细菌是与真核生物进化距离最近的原核生物。然而,真核生物祖先的身份以及线粒体起源的时间等核心问题仍是学术界争论的焦点。本文结合近年来国内外研究成果,从生命之树的形态变化与真核生物演变的具体机制两个角度梳理了目前对真核生物起源的认知过程、现有水平和研究前景,以期为揭示真核生物起源进程的后续研究提供参考与指引。.
Keywords: Asgard superphylum; archaea; endosymbiosis; eukaryogenesis; mitochondria; three domains; tree of life; two domains.