RNA silencing is an essential antiviral defense system in plants. Triggered by doublestranded RNA, silencing results in degradation or translational repression of target RNA. Viruses are inducers and targets of RNA silencing. To condition susceptibility, most plant viruses encode silencing suppressor proteins that interfere with RNA silencing. Tomato spotted wilt virus (TSWV) NSs protein is an RNA silencing suppressor. The mechanism of RNA silencing suppression by NSs and its role in virus infection and movement remain to be determined. We cloned NSs from the Hawaii isolate of TSWV. Using two independent assays, we show that NSs restored pathogenicity and supported the formation of local infection foci by suppressor-deficient Turnip mosaic virus (TuMV) and Turnip crinkle virus (TCV). Suppression of silencing directed against heterologous viruses establishes the foundation to determine the mechanism of antiviral RNA silencing suppression by NSs
