![]() Several popular drawings of the universal tree of life are widespread in the scientific literature and textbooks. A robust universal tree is critical to make sense of the evolution of the several types of lipids, cell envelopes and surface structures that originated and evolved on top of this continuity. This implies a fascinating continuity in the heredity of the cell membrane from LUCA to modern members of the three domains. The universal tree of ribosome-encoding organisms contains cellular organisms that, unlike viruses, reproduce via cell cycles that imply the formation of new cells from the division of mother cells. However, this should not be viewed as neglecting the role of viruses in biological evolution because “ the tree of life is infected by viruses from the root to the leaves” ( Forterre et al., 2014a). Viruses (capsid encoding organisms) are polyphyletic, therefore their evolution can be neither illustrated by a single tree nor included in the universal tree as additional domains ( Forterre et al., 2014a). I will draw a “universal tree” limited to ribosome-encoding organisms ( Raoult and Forterre, 2008) that diverged from the last universal common ancestor (LUCA). In this paper, I thus try to propose updated versions of the universal tree that include as many features as possible validated by robust phylogenetic analyses and/or comparative molecular biology and biochemistry. Thus, it will be difficult to draw a consensus tree welcomed by all scientists in the field. This is a daunting task indeed, given that the concept of a universal “tree” is disputed by some scientists, who have suggested replacing trees with networks, and that major features of the tree are still controversial ( Gribaldo et al., 2010 Forterre, 2012). ![]() The editors of research topic on “ archaeal cell envelopes and surface structures” gave me the challenging task of drawing an updated version of the universal tree of life. These trees, that will be easily updated as new data become available, could be useful to discuss controversial scenarios regarding early life evolution. Finally, I present a detailed tree of the domain Archaea, proposing the sub-phylum neo-Euryarchaeota for the monophyletic group of euryarchaeota containing DNA gyrase. Viruses are not indicated in these trees but are intrinsically present because they infect the tree from its roots to its leaves. This last scenario assumes the transformation of a modern domain into another, a controversial evolutionary pathway. A consensus version, in which each of the three domains is unrooted, and a version in which eukaryotes emerged within archaea are also presented. ![]() The tree is rooted between Bacteria and Arkarya, a new name proposed for the clade grouping Archaea and Eukarya. I propose here an updated version of Woese’s universal tree that includes several rootings for each domain and internal branching within domains that are supported by recent phylogenomic analyses of domain specific proteins. These proposals are misleading, suggesting that endosymbiosis can modify the shape of a tree or that viruses originated from the last universal common ancestor (LUCA). Several authors have proposed to replace the traditional universal tree with a ring of life, whereas others have proposed more recently to include viruses as new domains. Several universal trees based on ribosomal RNA sequence comparisons proposed at the end of the last century are still widely used, although some of their main features have been challenged by subsequent analyses. It is indeed a priori possible to construct an organismal tree connecting the three major domains of ribosome encoding organisms: Archaea, Bacteria and Eukarya, since they originated by cell division from LUCA. 2Institut de Biologie Intégrative de la cellule, Université Paris-Saclay, Paris, Franceīiologists used to draw schematic “universal” trees of life as metaphors illustrating the history of life.1Unité de Biologie Moléculaire du Gène chez les Extrêmophiles, Département de Microbiologie, Institut Pasteur, Paris, France.
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