title: The pre-endosymbiont hypothesis: a new perspective on the origin and evolution of mitochondria.
abstract: Mitochondrial DNA (mtDNA) is unquestionably the remnant of an α-proteobacterial genome, yet only ~10%-20% of mitochondrial proteins are demonstrably α-proteobacterial in origin (the "α-proteobacterial component," or APC). The evolutionary ancestry of the non-α-proteobacterial component (NPC) is obscure and not adequately accounted for in current models of mitochondrial origin. I propose that in the host cell that accommodated an α-proteobacterial endosymbiont, much of the NPC was already present, in the form of a membrane-bound metabolic organelle (the premitochondrion) that compartmentalized many of the non-energy-generating functions of the contemporary mitochondrion. I suggest that this organelle also possessed a protein import system and various ion and small-molecule transporters. In such a scenario, an α-proteobacterial endosymbiont could have been converted relatively directly and rapidly into an energy-generating organelle that incorporated the extant metabolic functions of the premitochondrion. This model (the "pre-endosymbiont hypothesis") effectively represents a synthesis of previous, contending mitochondrial origin hypotheses, with the bulk of the mitochondrial proteome (much of the NPC) having an endogenous origin and the minority component (the APC) having a xenogenous origin.
authors.affiliation: Centre for Comparative Genomics and Evolutionary Bioinformatics, Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia B3M 4R2, Canada.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Gray
mesh_terms: D020561:Alphaproteobacteria / Q000235:genetics; D005075:Biological Evolution; D004272:DNA, Mitochondrial / Q000737:chemistry; D016680:Genome, Bacterial; D054629:Genome, Mitochondrial; D008928:Mitochondria / Q000235:genetics* / Q000502:physiology / Q000648:ultrastructure; D010802:Phylogeny; D013559:Symbiosis
chemical_list: D004272:DNA, Mitochondrial