Route of NCLDV evolution: the genomic accordion

- General presentation of the NCLDV family.
- Description of the main evolutionary forces acting on their genomes (gene duplications and deletions, gene transfers, movement of mobile elements).
- NCLDV genomes evolve as genomic accordions with successive steps of expansion and shrinkage.

Nucleo cytoplasmic large DNA virus (NCLDV) superfamily forms a diverse group of viruses that infects a wide range of eukaryotic hosts (e.g. vertebrates, insects, protests, etc.). These viruses are characterized by a huge range in genome size (between 100 kb and 1.2 Mb), coupled with an extraordinary diverse genomic repertoire. Here I will review some recent results that shed light on the origin and genome evolution of these viruses, introducing the idea that these viruses evolved using a complex process of genomic accordion that imply successive steps of genome expansions (duplication and gene transfers) and genome reduction, in addition to movement and amplification of diverse mobile genetic elements.