DNA polymerases (DNAPs) synthesize DNA from deoxyribonucleotides in a semi-conservative manner and serve as the core of DNA replication and repair machineries. In eukaryotic cells, there are two genome-containing organelles, mitochondria and plastids, that were derived from an alphaproteobacterium and a cyanobacterium, respectively. Except for rare cases of genome-lacking mitochondria and plastids, both organelles must be served by nucleus-encoded DNAPs that localize and work in them to maintain their genomes. The evolution of organellar DNAPs has yet to be fully understood because of two unsettled issues. First, the diversity of organellar DNAPs has not been elucidated in the full spectrum of eukaryotes. Second, it is unclear when the DNAPs that were used originally in the endosymbiotic bacteria giving rise to mitochondria and plastids were discarded, as the organellar DNAPs known to date show no phylogenetic affinity to those of the extant alphaproteobacteria or cyanobacteria. In this study, we identified from diverse eukaryotes 134 family A DNAP sequences, which were classified into 10 novel types, and explored their evolutionary origins. The subcellular localizations of selected DNAPs were further examined experimentally. The results presented here suggest that the diversity of organellar DNAPs has been shaped by multiple transfers of the PolI gene from phylogenetically broad bacteria, and their occurrence in eukaryotes was additionally impacted by secondary plastid endosymbioses. Finally, we propose that the last eukaryotic common ancestor may have possessed two mitochondrial DNAPs, POP and a candidate of the direct descendant of the proto-mitochondrial DNAP, rdxPolA, identified in this study.

中文翻译：

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位于细胞器中的 A 家族 DNA 聚合酶百科全书：包括原线粒体在内的细菌的进化贡献

DNA聚合酶（DNAP）以半保守方式从脱氧核糖核苷酸合成DNA，并作为DNA复制和修复机制的核心。在真核细胞中，有两种含有基因组的细胞器：线粒体和质体，它们分别源自α变形菌和蓝细菌。除了罕见的缺乏基因组线粒体和质体的情况外，这两种细胞器都必须由核编码的 DNAP 提供服务，这些 DNAP 定位并在其中发挥作用以维持其基因组。由于两个未解决的问题，细胞器 DNAP 的进化尚未完全了解。首先，真核生物全谱中细胞器 DNAP 的多样性尚未得到阐明。其次，尚不清楚最初用于产生线粒体和质体的内共生细菌中的DNAP何时被丢弃，因为迄今为止已知的细胞器DNAP与现存的α变形菌或蓝细菌的DNAP没有系统发育亲和力。在这项研究中，我们从不同的真核生物中鉴定了134个A家族DNAP序列，将其分为10个新类型，并探讨了它们的进化起源。通过实验进一步检查了选定 DNAP 的亚细胞定位。这里提出的结果表明，细胞器 DNAP 的多样性是由来自系统发育广泛的细菌的 PolI 基因的多次转移形成的，并且它们在真核生物中的出现还受到次生质体内共生的影响。最后，我们提出，最后的真核生物共同祖先可能拥有两个线粒体 DNAP（POP）和本研究中确定的原线粒体 DNAP 直系后代的候选者 rdxPolA。