Laboratório de Genética Evolutiva Paulo Leminski, Centro de Ciências Exatas e da Natureza, Universidade Federal da Paraíba, João Pessoa, Paraíba, Brazil; Network of Researchers on the Chemical Evolution of Life (NoRCEL), Leeds, LS7 3RB, UK.
Theoretical Biology Group, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, D.F. C.P. 04510, México, USA.
Biosystems. 2021 Apr;202:104371. doi: 10.1016/j.biosystems.2021.104371. Epub 2021 Jan 30.
Cells occupy a prominent place in the history of life in Earth. The central role of cellular organization can be understood by the fact that "cellular life" is often used as a synonym for life itself. Thus, most characteristics used to define cell overlap with those ones used to define life. However, innovative scenarios for the origin of life are bringing alternative views to describe how cells may have evolved from the open biological systems named progenotes. Here, using a logical and conceptual analysis, we re-evaluate the characteristics used to infer a single origin for cells. We argue that some evidences used to support cell monophyly, such as the presence of elements from the translation mechanism together with the universality of the genetic code, actually indicate a unique origin for all "biological systems", a term used to define not only cells, but also viruses and progenotes. Besides, we present evidence that at least two biochemical pathways as important as (i) DNA replication and (ii) lipid biosynthesis are not homologous between Bacteria and Archaea. The identities observed between the proteins involved in those pathways along representatives of these two ancestral domains of life are too low to indicate common genic ancestry. Altogether these facts can be seen as an indication that cellular organization has possibly evolved two or more times and that LUCA (the Last Universal Common Ancestor) may not have existed as a cellular entity. Thus, we aim to consider the possibility that different strategies acquired by biological systems to exist, such as viral, bacterial and archaeal were most likely originated independently from the evolution of different progenote populations.
细胞在地球生命史上占据着重要地位。细胞组织的核心作用可以理解为，“细胞生命”通常被用作生命本身的同义词。因此，用于定义细胞的大多数特征与用于定义生命的特征重叠。然而，生命起源的创新方案带来了替代观点，描述了细胞如何可能从名为原核生物的开放生物系统中进化而来。在这里，我们使用逻辑和概念分析，重新评估用于推断细胞单一起源的特征。我们认为，一些用于支持细胞单系发生的证据，例如翻译机制的元素的存在以及遗传密码的普遍性，实际上表明所有“生物系统”都有一个独特的起源，这个术语不仅用于定义细胞，还用于定义病毒和原核生物。此外，我们还提出了证据表明，至少有两种与（i）DNA 复制和（ii）脂质生物合成一样重要的生化途径在细菌和古菌之间没有同源性。这些两种生命古老领域的代表物之间涉及这些途径的蛋白质的同一性太低，无法表明共同的基因祖先。所有这些事实都可以被视为细胞组织可能已经进化了两次，并且 LUCA（最后的普遍共同祖先）可能没有作为细胞实体存在的迹象。因此，我们的目标是考虑这样一种可能性，即生物系统为了生存而采用的不同策略，如病毒、细菌和古菌，很可能是从不同原核生物种群的进化中独立起源的。
