Insights into Genome Evolution of Giant Viruses

In contrast to most viruses with only a small number of genes, the emerging group of giant viruses can have hundreds to thousands of genes per genome. They infect diverse eukaryotes, causing animal diseases such as African swine fever and algal population demise in marine blooms. To better understand how their genomes evolved, we employed large-scale analyses to dissect giant virus gene repertoires. We found that the ancestors of giant viruses had small genomes for a long time until relatively recently, when multiple lineages parallelly accumulated large amounts of genes during the adaptation to various eukaryotic hosts that led to viral genome gigantism. This study explains why different giant virus lineages infecting the same host can have very dissimilar gene repertoires and sheds light on the origin of giant viruses and their coevolutionary relationships with eukaryotes.