Akanni Wasiu A, Siu-Ting Karen, Creevey Christopher J, McInerney James O, Wilkinson Mark, Foster Peter G, Pisani Davide
School of Biological Sciences and School of Earth Sciences, University of Bristol, Life Sciences Building, Bristol BS8 1TG, UK Department of Biology, National University of Ireland, Maynooth, Co. Kildare, Ireland Department of Life Science, The Natural History Museum, London SW7 5BD, UK.
School of Biological Sciences and School of Earth Sciences, University of Bristol, Life Sciences Building, Bristol BS8 1TG, UK Department of Biology, National University of Ireland, Maynooth, Co. Kildare, Ireland Department of Life Science, The Natural History Museum, London SW7 5BD, UK Institute of Biological, Environmental and Rural Sciences (IBERS), Aberystwyth University, Aberystwyth, Ceredigion SY23 3FG, UK.
Philos Trans R Soc Lond B Biol Sci. 2015 Sep 26;370(1678):20140337. doi: 10.1098/rstb.2014.0337.
The origin of the eukaryotic cell is considered one of the major evolutionary transitions in the history of life. Current evidence strongly supports a scenario of eukaryotic origin in which two prokaryotes, an archaebacterial host and an α-proteobacterium (the free-living ancestor of the mitochondrion), entered a stable symbiotic relationship. The establishment of this relationship was associated with a process of chimerization, whereby a large number of genes from the α-proteobacterial symbiont were transferred to the host nucleus. A general framework allowing the conceptualization of eukaryogenesis from a genomic perspective has long been lacking. Recent studies suggest that the origins of several archaebacterial phyla were coincident with massive imports of eubacterial genes. Although this does not indicate that these phyla originated through the same process that led to the origin of Eukaryota, it suggests that Archaebacteria might have had a general propensity to integrate into their genomes large amounts of eubacterial DNA. We suggest that this propensity provides a framework in which eukaryogenesis can be understood and studied in the light of archaebacterial ecology. We applied a recently developed supertree method to a genomic dataset composed of 392 eubacterial and 51 archaebacterial genera to test whether large numbers of genes flowing from Eubacteria are indeed coincident with the origin of major archaebacterial clades. In addition, we identified two potential large-scale transfers of uncertain directionality at the base of the archaebacterial tree. Our results are consistent with previous findings and seem to indicate that eubacterial gene imports (particularly from δ-Proteobacteria, Clostridia and Actinobacteria) were an important factor in archaebacterial history. Archaebacteria seem to have long relied on Eubacteria as a source of genetic diversity, and while the precise mechanism that allowed these imports is unknown, we suggest that our results support the view that processes comparable to those through which eukaryotes emerged might have been common in archaebacterial history.
真核细胞的起源被认为是生命史上主要的进化转变之一。目前的证据有力地支持了一种真核生物起源的设想，即两种原核生物，一种古细菌宿主和一种α-变形菌（线粒体的自由生活祖先），进入了稳定的共生关系。这种关系的建立与嵌合化过程相关，在此过程中，来自α-变形菌共生体的大量基因转移到了宿主细胞核中。长期以来，一直缺乏一个能从基因组角度对真核生物起源进行概念化的总体框架。最近的研究表明，几个古细菌门的起源与大量真细菌基因的导入同时发生。虽然这并不表明这些门是通过导致真核生物起源的相同过程产生，但这表明古细菌可能普遍倾向于将大量真细菌DNA整合到其基因组中。我们认为，这种倾向提供了一个框架，据此可以根据古细菌生态学来理解和研究真核生物起源。我们将一种最近开发的超树方法应用于一个由392个真细菌属和51个古细菌属组成的基因组数据集，以测试从真细菌流入的大量基因是否确实与主要古细菌分支的起源同时发生。此外，我们在古细菌树的基部发现了两个方向不确定的潜在大规模转移。我们的结果与先前的发现一致，并似乎表明真细菌基因的导入（特别是来自δ-变形菌、梭菌和放线菌）是古细菌历史中的一个重要因素。古细菌似乎长期以来一直依赖真细菌作为遗传多样性的来源，虽然允许这些导入的精确机制尚不清楚，但我们认为我们的结果支持这样一种观点，即在古细菌历史中，类似于真核生物出现的过程可能很常见。
