Blackstone Neil W
Department of Biological Sciences, Northern Illinois University, DeKalb, Illinois, 60115.
Evolution. 1995 Oct;49(5):785-796. doi: 10.1111/j.1558-5646.1995.tb02315.x.
Discussions of mitochondria and their hosts often conceptualize this relationship in a more or less modern form, focusing on the metabolic benefits of mitochondria to the host cell or on the possibility of intragenomic conflict. A more inclusive units-of-evolution perspective recognizes that both costs and benefits must be viewed from the level of the cells that initiated this interaction, the protomitochondrion and the primitive host cell. From this perspective, ecological and physiological considerations become central to the characterization of initial and subsequent host-mitochondria associations. Foremost among these considerations is the generation of superoxide radicals by modern mitochondria and the deleterious effects of these endogenous oxidants on modern eukaryotic cells. Because of their photosynthetic and aerobic ecologies, protomitochondria likely were relatively tolerant of such oxidants; anaerobic, heterotrophic, primitive host cells, on the other hand, likely were not. In the initial association of host and symbiont, the latter may have manipulated the former's life history by means of both endogenous oxidants and a superabundance of ATP. A resolution of this units-of-evolution conflict was necessary to continue this association, and this resolution, in a ritualized form, may have shaped the evolution of many features of modern eukaryotic cells and mitochondria, for example, the messenger functions of calcium ions, the regulatory role of phosphorylation cascades in cell-division cycles, the absence from the mitochondrial genome of replication factors, transcription factors, and adenine nucleotide carrier genes. The initial host-mitochondria interaction may have further channeled the evolution of multicellular eukaryotes, particularly animals, resulting in the association of mitochondria and the germinal plasm and in the use of extracellular ATP and endogenous oxidants as developmental signals. Evolutionary explanations for "free-radical" theories of development and aging are thus suggested.
关于线粒体及其宿主的讨论，常常以或多或少现代的形式来概念化这种关系，聚焦于线粒体对宿主细胞的代谢益处或基因组内冲突的可能性。一个更具包容性的进化单位视角认识到，成本和益处都必须从发起这种相互作用的细胞层面来审视，即原始线粒体和原始宿主细胞。从这个角度看，生态和生理方面的考量成为最初及后续宿主 - 线粒体关联特征描述的核心。这些考量中首要的是现代线粒体产生超氧自由基以及这些内源性氧化剂对现代真核细胞的有害影响。由于其光合和需氧生态，原始线粒体可能对这类氧化剂相对耐受；另一方面，厌氧、异养的原始宿主细胞可能并非如此。在宿主与共生体的最初关联中，后者可能通过内源性氧化剂和过量的ATP来操控前者的生命历程。解决这种进化单位冲突对于延续这种关联是必要的，而这种以仪式化形式的解决方式，可能塑造了现代真核细胞和线粒体许多特征的进化，例如钙离子的信使功能、磷酸化级联反应在细胞分裂周期中的调节作用、线粒体基因组中复制因子、转录因子和腺嘌呤核苷酸载体基因的缺失。最初的宿主 - 线粒体相互作用可能进一步引导了多细胞真核生物，尤其是动物的进化，导致线粒体与生殖质的关联以及将细胞外ATP和内源性氧化剂用作发育信号。因此，有人提出了对发育和衰老的“自由基”理论的进化解释。
