Department of Life Sciences, College of Health, Medicine and Life Sciences, Brunel University London, Uxbridge, UB8 3PH, United Kingdom.
Biosystems. 2021 Apr;202:104353. doi: 10.1016/j.biosystems.2021.104353. Epub 2021 Jan 13.
Serial Endosymbiosis Theory, or SET, was conceived and developed by Lynn Margulis, to explain the greatest discontinuity in the history of life, the origin of eukaryotic cells. Some predictions of SET, namely the origin of mitochondria and chloroplasts, withstood the test of the most recent evidence from a variety of disciplines including phylogenetics, biochemistry, and cell biology. Even though some other predictions fared less well, SET remains a seminal theory in biology. In this paper, I focus on two aspects of SET. First, using the concept of "universal symbiogenesis", developed by Freeman Dyson to search for commonalities in astronomy and biology, I propose that SET can be extended beyond eukaryogenesis. The extension refers to the possibility that even prokaryotic organisms, themselves subject to the process of symbiogenesis in SET, could have emerged symbiotically. Second, I contrast a recent "viral eukaryogenesis" hypothesis, according to which the nucleus evolved from a complex DNA virus, with a view closer to SET, according to which the nucleus evolved through the interplay of the archaeal host, the eubacterial symbiont, and a non-LTR transposon, or telomerase. Viruses joined in later, through the process of viral endogenization, to shape eukaryotic chromosomes in the process of karyotype evolution. These two proposals based on SET are a testament to its longevity as a scientific theory.
内共生体连续进化理论（Serial Endosymbiosis Theory，简称 SET）由 Lynn Margulis 提出并发展，用于解释生命史上最大的不连续性，即真核细胞的起源。SET 的一些预测，如线粒体和叶绿体的起源，经受住了来自系统发生学、生物化学和细胞生物学等多个学科的最新证据的检验。尽管其他一些预测表现不佳，但 SET 仍然是生物学中的一个重要理论。在本文中，我将重点关注 SET 的两个方面。首先，我利用 Freeman Dyson 提出的“普遍共生进化”概念，来寻找天文学和生物学之间的共性，从而提出 SET 可以超越真核生物起源的范畴。这种延伸指的是，即使是原核生物，它们本身也受到 SET 中共生进化过程的影响，也有可能通过共生进化而出现。其次，我对比了最近的“病毒真核生物起源”假说，该假说认为细胞核是从一种复杂的 DNA 病毒进化而来的，而 SET 则认为细胞核是通过古菌宿主、真细菌共生体和非 LTR 转座子或端粒酶的相互作用进化而来的。病毒后来通过病毒内共生的过程，参与了真核染色体的形成，并在核型进化过程中塑造了真核染色体。这两个基于 SET 的建议证明了它作为一种科学理论的持久生命力。
