Immunization by mobile virus-derived siRNAs is crucial for plant antiviral silencing

Ascertaining this role is challenging because it requires uncoupling vsiRNA mobility from viral movement while preserving viral virulence. Consequently, the contribution of non-cell-autonomous RNAi to plant antiviral immunity remains essentially unknown.

Here, we investigated the naturally phloem-restricted infection of turnip yellows virus (TuYV) in the stereotypical Arabidopsis root system at cellular resolution. We uncovered intertwined, complex mechanisms operating in both vsiRNA-emitting and -recipient cells, that drive reiterated short-range (~3-4 cell) immunization events. We found that, while intracellular antiviral RNAi is nullified by TuYV, non-cell-autonomous immunization accounts mainly —if not exclusively— for the containment of viral tissue invasion, titers and symptoms severity at the whole-plant scale.