线粒体起源于一个古老的内共生,涉及一个α变形杆菌。1,2,3随着时间的推移,这些细胞器大量降低了它们的基因含量,大多数基因在最后一个真核生物共同祖先(LECA)之前转移到宿主细胞核。4这个过程在现代有丝分裂基因组中产生了不同的基因组成,包括在某些极端情况下,该细胞器基因组的完全丧失。5,6,7,8,9,10,11,12,13,14在光谱的另一端,Jakobids拥有最丰富基因的有丝分裂基因组,编码60-66蛋白质8这里,我们为大家介绍了棘藻的有丝分裂基因组,来自深枝CRUMs超群的原生生物。15,16值得注意的是,它拥有除jakobids外最富含基因的有丝分裂基因组,通过容纳91个基因,包括62个蛋白质编码。其中包括细菌型细胞色素c成熟系统I的四个亚基的稀有同源物(CcmA,CcmB,CcmC,和CcmF)以及独特的核糖体蛋白S6。在线粒体的早期进化过程中,由于系统促进了宿主细胞质中合成的蛋白质转运回线粒体,因此基因从原始线粒体内共生体转移到细胞核成为可能。除了普遍发现的真核蛋白质进口系统,据报道,jakobid有丝分裂基因组独特地编码Sec一般分泌途径的SecY跨膜蛋白,然而,其进化起源尚不清楚。Mantamonas有丝分裂基因组不仅编码SecY,还编码SecA,SecE,还有SecG,使其成为已知的唯一真核生物,以容纳完整的线粒体Sec易位系统。此外,我们的系统发育和比较基因组分析为该系统的α-蛋白质细菌起源提供了令人信服的证据,在LECA建立其存在。
Mitochondria originated from an ancient endosymbiosis involving an alphaproteobacterium.1,2,3 Over time, these organelles reduced their gene content massively, with most genes being transferred to the host nucleus before the last eukaryotic common ancestor (LECA).4 This process has yielded varying gene compositions in modern mitogenomes, including the complete loss of this organellar genome in some extreme cases.5,6,7,8,9,10,11,12,13,14 At the other end of the spectrum, jakobids harbor the most gene-rich mitogenomes, encoding 60-66 proteins.8 Here, we introduce the
mitogenome of Mantamonas sphyraenae, a protist from the deep-branching CRuMs supergroup.15,16 Remarkably, it boasts the most gene-rich
mitogenome outside of jakobids, by housing 91 genes, including 62 protein-coding ones. These include rare homologs of the four subunits of the bacterial-type cytochrome c maturation system I (CcmA, CcmB, CcmC, and CcmF) alongside a unique ribosomal protein S6. During the early evolution of mitochondria, gene transfer from the proto-mitochondrial endosymbiont to the nucleus became possible thanks to systems facilitating the transport of proteins synthesized in the host cytoplasm back to the mitochondrion. In addition to the universally found eukaryotic protein import systems, jakobid mitogenomes were reported to uniquely encode the SecY transmembrane protein of the Sec general secretory pathway, whose evolutionary origin was however unclear. The Mantamonas
mitogenome not only encodes SecY but also SecA, SecE, and SecG, making it the sole eukaryote known to house a complete mitochondrial Sec translocation system. Furthermore, our phylogenetic and comparative genomic analyses provide compelling evidence for the alphaproteobacterial origin of this system, establishing its presence in LECA.