‘A tale of two viral lineages : evolution of viruses and the cellular universal tree of life
Anthony WOO / Unit : Molecular Biology of Genes in Extremophiles headed by Patrick Forterre
Over the past two decades, many new viruses have been identified in diverse habitats, providing important insights into the diversity and ecology of the virosphere. However, there is still much debate concerning the origins of viruses in the evolutionary history of life. Studying virus origin and evolution is a challenging exercise, especially when addressing early co-evolution with cellular domains. While cellular domains (Archaea, Bacteria, and Eukarya) have been established based on ribosome sequences, viral lineages have been classified based on the conservation of their major capsid proteins (MCPs) structure. There are two categories of viral lineage: domain-specific (identified in one domain only) and cosmopolitan lineages (identified in hosts from more than one domain). To date, only two cosmopolitan lineages were discovered across the three domains of life, namely the HK97 and the PRD1-adenovirus lineages. The HK97 lineage consists of viruses such as head-tailed viruses and herpesviruses, whereas the PRD1-adenovirus lineage encompasses giant viruses as well as smaller viruses such as bacteriophage PRD1. Here we analyzed the evolutionary history of these lineages and found that the viral tree of life is incongruent with the cellular universal tree of life, raising various evolutionary scenarios that could explain this paradox.
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