||2:00pm Mar 06, 2020
CNRS/Aix-Marseille University, France
The DNA Methylation Landscape of Giant Viruses
DNA methylation is an important epigenetic mark that contributes to various regulations in all domains of life. Prokaryotes for instance use it through Restriction-Modification (R-M) systems as a host-defense mechanism against viruses. Giant viruses are widespread dsDNA viruses infecting eukaryotes with gene contents overlapping the cellular world. Genomic and metagenomic data have increasingly been released on these viruses, showing that they are widespread on the planet. But while most of them encode DNA methyltransferases (MTases), virtually nothing is known about their epigenomes. In this talk I will present our recent work on the epigenomes of giant viruses. Using single-molecule real-time sequencing we studied the complete DNA methylome of a large spectrum of families: the Marseilleviridae, the Pandoraviruses, the Molliviruses, the Mimiviridae along with their associated virophages and transpoviron, the Pithoviruses and the Cedratviruses (of which we report a new strain). We showed that DNA methylation is widespread in giant viruses although unevenly distributed. We then identified the corresponding viral MTases, all of which are of bacterial origins and subject to intricate gene transfers between bacteria, viruses and their eukaryotic host. If some viral MTases undergo pseudogenization, most are conserved, functional and under purifying selection, suggesting that they increase the viruses’ fitness. In Marseilleviridae, encoded MTases are paired with cognate restriction endonucleases (REases) forming complete R-M systems. Our data suggest that giant viruses’ MTases are involved in different kind of virus-pathogens interactions during coinfections.