Seasonality of interactions between a plant virus and its host during persistent infection in a natural environment.

Persistent infection, wherein a pathogen is continually present in a host individual, is widespread in virus-host systems. However, little is known regarding how seasonal environments alter virus-host interaction during such metastability. We observed a lineage-to-lineage infection of the host plant Arabidopsis halleri with Turnip mosaic virus for 3 years without severe damage. Virus dynamics and virus-host interactions within hosts were highly season dependent. Virus accumulation in the newly formed leaves was temperature dependent and was suppressed during winter. Transcriptome analyses suggested that distinct defence mechanisms, i.e. salicylic acid (SA)-dependent resistance and RNA silencing, were predominant during spring and autumn, respectively. Transcriptomic difference between infected and uninfected plants other than defence genes appeared transiently only during autumn in upper leaves. However, the virus preserved in the lower leaves is transferred to the clonal offspring of the host plants during spring. In the linage-to-linage infection of the A. halleri-TuMV system, both host clonal reproduction and virus transmission into new clonal rosettes are secured during the winter-spring transition. How virus and host overwinter turned out to be critical for understanding a long-term virus-host interaction within hosts under temperate climates, and more generally, understanding seasonality provides new insight into ecology of plant viruses.