Wang Zhang, Wu Martin
Department of Biology, University of Virginia, Charlottesville, Virginia, United States of America.
PLoS One. 2014 Oct 15;9(10):e110685. doi: 10.1371/journal.pone.0110685. eCollection 2014.
Reconstruction of mitochondrial ancestor has great impact on our understanding of the origin of mitochondria. Previous studies have largely focused on reconstructing the last common ancestor of all contemporary mitochondria (proto-mitochondria), but not on the more informative pre-mitochondria (the last common ancestor of mitochondria and their alphaproteobacterial sister clade). Using a phylogenomic approach and leveraging on the increased taxonomic sampling of alphaproteobacterial and eukaryotic genomes, we reconstructed the metabolisms of both proto-mitochondria and pre-mitochondria. Our reconstruction depicts a more streamlined proto-mitochondrion than these predicted by previous studies, and revealed several novel insights into the mitochondria-derived eukaryotic metabolisms including the lipid metabolism. Most strikingly, pre-mitochondrion was predicted to possess a plastid/parasite type of ATP/ADP translocase that imports ATP from the host, which posits pre-mitochondrion as an energy parasite that directly contrasts with the current role of mitochondria as the cell's energy producer. In addition, pre-mitochondrion was predicted to encode a large number of flagellar genes and several cytochrome oxidases functioning under low oxygen level, strongly supporting the previous finding that the mitochondrial ancestor was likely motile and capable of oxidative phosphorylation under microoxic condition.
线粒体祖先的重建对我们理解线粒体的起源具有重大影响。以往的研究主要集中在重建所有当代线粒体的最后共同祖先（原线粒体），而不是更具信息性的前线粒体（线粒体及其α-变形菌姐妹进化枝的最后共同祖先）。我们采用系统基因组学方法，并利用α-变形菌和真核生物基因组分类取样的增加，重建了原线粒体和前线粒体的代谢。我们的重建描绘了一个比以往研究预测的更简化的原线粒体，并揭示了对线粒体衍生的真核生物代谢（包括脂质代谢）的几个新见解。最引人注目的是，预测前线粒体拥有一种质体/寄生虫类型的ATP/ADP转位酶，可从宿主导入ATP，这将前线粒体定位为一种能量寄生虫，这与线粒体目前作为细胞能量生产者的角色形成直接对比。此外，预测前线粒体编码大量鞭毛基因和几种在低氧水平下起作用的细胞色素氧化酶，有力地支持了先前的发现，即线粒体祖先可能具有运动能力，并且能够在微氧条件下进行氧化磷酸化。
