The portrait of LUCA and the topology of the tree of life
Based on algorithmic analyses of thousands of proteins shared by these two domains, it has been recently suggested that LUCA (the last Universal Common Ancestor) was rather similar to modern Bacteria and Archaea living at high temperature (1). However, focusing on comparative molecular biology and careful analysis of some critical proteins, such as reverse gyrase, the most parsimonious scenario suggests that LUCA was not a hyperthermophile and was much simpler than modern organisms, with possibly still an RNA genome (2, 3). This explains why the evolutionary tempo was much faster at the time of LUCA than during the diversification of the three domains. The debate about the position of eucaryotes in the tree of life, has also important implications to draw the portrait of LUCA. If Archaea and Eucarya are sister group, as suggested by our analyses (4), some eucaryotic features might have been present in LUCA and later lost in Archaea and Bacteria. The nature of the LUCA virome is another matter of debate. To explain the odd distribution pattern of DNA viruses in the tree of life, I recently suggested that DNA viruses only originated during the diversification of the three domains from an RNA-based LUCA (3).
1) Moody et al., 2024, Nat Ecol Evol, PMID: 38997462
2) Catchpole and Forterre, 2019, PMID: 31504731
3) Forterre, 2024, J.Mol Evol, PMID: 39158619
4) Da Cunha et al., 2022, mlife, PMID: 38818326
Prof. Patrick Forterre is presently honorary professor at the Institut Pasteur and emeritus Professor at the University Paris-Saclay. Patrick Forterre started working on DNA replication and DNA topology in Bacteria. Inspired by Carl Woese’s work, he turned out to study these mechanisms in Archaea (formerly archaebacteria). His first major contribution was the characterization of reverse gyrase, a novel type of DNA topoisomerase that introduces positive superturns into DNA. He could show that reverse gyrase is the only protein essential for life at high temperature. Patrick Forterre defended his Habilitation in 1985 at the University of Paris VII and become Professor at the University of Orsay where he set up his own laboratory in 1989. In 1997, his team discovered the enzyme that triggers meiotic recombination in eukaryotes, SPO11, thanks to their work on archaeal DNA topoisomerase. In 2000, they identified the first DNA replication origin in Archaea. In 2004, Patrick Forterre became head of the Microbiology Department at the Insitute Pasteur in Paris. He invited David Prangishvili to work with him on archaeal viruses in Pasteur. They described several new viral families and a fascinating new mechanism of virus egress. In 2014, he received a five year ERC award to study virus-like vesicles in Archaea.
The interest of Patrick Forterre for Archaea was early on boosted by their pivotal position in the universal tree of life. He promoted the name LUCA, for the Last Universal Common Ancestor. More recently, he revisited with his coworkers Violette Da Cunha and Morgan Gaia the phylogenies sugggesting that eukaryotes originated from Asgard archaea. Their work supports instead the classical Woese’s tree of life and suggest ancient gene exchanges between Asgard and the ancestors of modern eukaryotes.