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.

Our results demonstrate that rapid deletions of NIb occurred upon passaging in N. tabacum 35S::NIb. In two lineages, these variants reached high frequencies, comprising approximately a fourth of the population. These results are therefore a proof of principle that NIRV expression could have a similar effect on a virus population: allowing deletion mutants to be maintained in the virus populations, while also providing conditions in which these mutants could reach high frequencies. The immediate effect of these deletions will be that a part of the virus population is replication defective in host individuals that do not express the NIRV. This could have important ramifications for viral spread, and virus-host coevolution. On the other hand, the further evolution of a virus population in a host expressing virus genes may also be contingent upon the presence of genomic deletions in the viral genome.