Host age-dependent evolution of a plant RNA virus

Viruses are obligate pathogens that entirely rely on their host resources to complete their infectious cycle. The availability of such resources depends upon external and internal factors, being host age one of the most relevant ones. The interplay between host age and virus evolution has not been thoroughly studied in plants. Here, we have used the Arabidopsis thaliana - turnip mosaic virus (TuMV) pathosystem to study plant-virus interactions and virus evolution at three different host ages: vegetative (juvenile), bolting (transition) and reproductive (mature) stages. After infecting plants with a naïve and a well-adapted TuMV isolates, we observed that the older the host the faster and more severe the infections were. The same trend was observed for several other viruses. Thereafter, we experimentally evolved lineages of the naïve and the well-adapted TuMV isolates in plants from each of the three developmental stages. All evolved viruses enhanced their infection phenotypes, being this increase more intense on viruses evolved in younger hosts. The genomic changes of the evolved viral lineages revealed mutation patterns that strongly depended on the founder viral isolate as well as on the age of the host wherein the lineages evolved. ### Competing Interest Statement The authors have declared no competing interest.