Abstract
AbstractThe cellular theory on the nature of life has been one of the first major advancements in biology. Viruses, however, are the most abundant life forms, and their exclusion from mainstream biology and the Tree of Life (TOL) is a major paradox in biology. This article presents a broad, unifying scenario on the origin and evolution of cellular and viral domains that challenges the conventional views about the history of life and supports a TOL that includes viruses. Co-evolution of viruses and their host cells has led to some of the most remarkable developments and transitions in the evolution of life, including the origin of non-coding DNA as a genomic protective device against viral insertion damage. However, one of the major fundamental evolutionary developments driven by viruses was probably the origin of cellular domains - Bacteria, Archaea and Eukarya - from the Last Universal Common Ancestor (LUCA) lineage, by evolving anti-fusion mechanisms. Consistent with a novel fusion/fission model for the population mode of evolution of LUCA, this paper presents a “cell-like world” model for the origin of life. According to this model the evolution of coupled replication, transcription and translation system (RT&T) occurred within non-living cell-like compartments (CCs). In this model, the ancestral ribosome originated as template-based RNA synthesizing machinery. The origin of the cellular genome as a centralized unit for storage and replication of genetic information within the CCs facilitated the evolution of the ancestral ribosome into a powerful translation machinery - the modern ribosome. After several hundred millions of years of providing an enclosed environment and fusion/fission based exchanges necessary for the population mode of evolution of the basic metabolism and the RT&T, the CCs evolved into the first living entities on earth - the LUCA lineage. The paper concludes with a proposal for a TOL that integrates the co-evolution of cellular and viral domains. This is one of a series of three articles that present a unifying scenario on the origin and evolution of viral and cellular domains, including the origin of life, which has significant t bio-medical implications and could lead to a significant paradigm shift in biology.
Highlights
The cellular theory on the nature of life has been one of the first major advancements in biology
Viruses are not included in the Tree of Life (TOL), which represents exclusively the evolution of cellular domains - Archaea, Bacteria and Eukarya [14,15,16]
This scenario resembles the fusion model on the origin of viruses as molecular organisms from parasitic cellular species that fused with their host cells [4]. These early parasitic molecular organisms were probably the first members of the Last Universal Common Ancestor (LUCA) population to undergo reproductive isolation and speciation,leading to the origin of first viral lineages (Fig. 1). These viral species played a significant role in the eventual origin of the three cellular domains - Bacteria, Archaea, and Eukarya - which branched off the LUCA lineage by developing anti-fusion mechanisms, leading to their reproductive isolation and speciation
Summary
The cellular theory on the nature of life has been one of the first major advancements in biology. Based on a suggestion about the potential role of cellular hybridization, or fusion, in the early evolution of cells and the origin of ancestral viruses [17], it is proposed here that the LUCA lineage evolved in a population mode similar to that of sexually reproducing species. Organisms were probably the first members of the LUCA population to undergo reproductive isolation and speciation,leading to the origin of first viral lineages (Fig. 1) These viral species played a significant role in the eventual origin of the three cellular domains - Bacteria, Archaea, and Eukarya - which branched off the LUCA lineage by developing anti-fusion mechanisms, leading to their reproductive isolation and speciation. It took these compartments, which are referred to here as cell-like compartments (CCs), several hundreds of millions years of providing an enclosed environment and fusion/fission based exchanges necessary for the population mode of evolution (i.e., collective evolution) of basic metabolism and RT&T to evolve into genuine cells, the LUCA lineage
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