VIGS in tomato plants suggests a strong RNAi-based response of a local tomato variety to TSWV-RB infection.

Plant RNAi operates as a potent defence system where RNA-dependent RNA polymerases (RDRs) enzymes are core components of the pathways involved in siRNA biogenesis and responsible for the spread of the silencing signal on short and long distance. We used a Tobacco rattle virus (TRV) based virus-induced gene silencing (VIGS) system to investigate the role of RDR1 and RDR6 genes in response to viral infection supported by RB strains of Tomato spotted wilt virus (TSWV) in two tomato cultivars, LV and UC82, characterized by a different response to the disease. The RDR silencing resulted in an increased susceptibility to viral infection, in both cultivars, suggesting that the tolerance to TSWV observed in LV but not in UC82 involves a stronger RNAi-based response. Consistent with previous findings, RDR1 and RDR6 cooperated to limit primary infections and to prevent systemic invasion, indicating a synergistic interaction through the RNA silencing-based antiviral system. Transcriptome analysis suggests the propensity of both varieties to compensate the lower expression of the silenced gene through the over-expression of the other. Interesting, in plants with one RDR silenced gene, cv. LV exhibited the potential to counteract viral infection by an increased transcription level of the other nonsilenced gene compared with cv. UC82.