Within-host virus spreading and tolerance to infection are key factors of the Arabidopsis thaliana age-dependent susceptibility to viral infections

Arabidopsis thaliana is more susceptible to certain viruses during its later developmental stages. The reasons for this age-dependent susceptibility are not fully understood. Here we explored the possible causes by studying the A. thaliana infection response to turnip mosaic virus at three developmental stages: vegetative, bolting and flowering. We found that infected plants at later stages downregulate cell wall fortification genes and that this downregulation facilitates the viral spread and systemic infection. Despite being more susceptible to infection, infected flowering plants are more fertile (i.e., produce more viable seeds) than vegetative and bolting infected plants; that is, they have greater fitness than plants infected at these earlier developmental stages. Treatment of postbolting plants with salicylic acid increases resistance to infections at the cost of significantly reducing fertility. Together, these observations suggest a negative trade-off between viral susceptibility and plant fertility. Our findings point towards a development-dependent tolerance to infection.