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.

After 30 weeks of evolution, we measured virus accumulation of the evolved lineages ( fig. 3B ). The data were analyzed by ANOVA (table 1) , and we found no effect of the virus type (TEV or TEV-ÁNIb) on accumulation, although there was a strong effect of lineage. The significant lineage-dependent effects suggest that random factors have played an important role during evolution, implicating genetic drift effects due to short passage duration. When pairwise comparisons were made between the evolved lineages and their respective ancestral viruses, Lineage 1 of TEV-ÁNIb had a significantly lower accumulation (t-test with Holm-Bonferroni correction: t 7 ¼ 4.001, P ¼ 0.005). Accumulation of all other lineages was not significantly different from the ancestral virus, although the data suggest Lineage 3 and Lineage 5 of TEV-ÁNIb also have low accumulation ( fig. 3B ).