Suppression of post-transcriptional gene silencing intensifies pathogenicity of tomato torrado virus (ToTV) in Nicotiana benthamiana

Abstract

omato torrado virus (ToTV) is a whitefly-transmitted emerging pathogen infecting Solanum lycopersicum and inducing severe necrosis. To date, it was taken for granted that all plant viruses encode suppressors of silencing – proteins that promote disease symptoms in virusinfected plants. The main feature of silencing suppressors is to counteract plant defence mechanisms during infection. Interestingly, such a protein was not described so far for any known members from Torradovirus genus. In this study, we asked how ToTV infection would develop in a presence of a heterologusly expressed strong suppressor of silencing. For this, two experimental approaches were chosen. On one hand, ToTV accumulation was tested in Nicotiana benthmaniana plants stably expressing p19TBSV gene from tomato bushy stunt virus (TBSV) (the p19TBSV is a well-described silencing suppressor). On the other hand, the p19TBSV gene was introduced into ToTV genome to produce a recombined ToTV-Kra-p19 and its accumulation was assessed in the wild type N. benthamiana. We observed that ToTV induced more severe disease symptoms in N. benthamiana in a presence of the p19TBSV what was accompanied by a significantly higher accumulation of viral genomic RNAs. This indicates that the p19TBSV boosts ToTV pathogenicity. On the other hand, it points that the ToTV infectivity does not rely strictly on a presence of a strong silencing suppressor.