Shrinkage of Genome Size in a Plant RNA Virus upon Transfer of an Essential Viral Gene into the Host Genome

Tromas, Nicolas; Zwart, Mark P.; Forment, Javier; Elena, Santiago F.

Finally, it is fair to mention that our experimental system remains artificial to some extent. Although many examples of DNA viruses using host enzymes for replication exist (e.g., geminiviruses and polydnaviruses), no RNA virus has been described so far that does not encode for its own functional RdRp, even though certain plants encode functional RdRps of viral origin in their genomes, for example, the narnaviruslike RdRp found in the mitochondria of Arabidopsis thaliana (Hong et al. 1998) . In this respect, a critical reader may argue that RdRp was not the best choice for studying the pseudogenization of viral genes in the presence of a homologous NIRV. However, our results should be strong enough to convince such a reader that even a highly constrained gene, such as RdRp can be lost from viral genomes if provided in trans by the host.