Analysis of RNA-mediated virus resistance by NSs and NSm gene sequences from Tomato spotted wilt virus

Nicotiana benthamiana was transformed with the NSs gene sequence of Tomato spotted wilt virus (TSWV). When a non-silenced line showing high levels of the transgene expression was inoculated with Potato virus X (PVX) engineered to contain the NSs gene sequences, reduced transgene mRNA accumulation was observed. RNA silencing was the underlying mechanism for the reduction. Previously, non-transgenic N. benthamiana infected with PVX engineered to contain the nucleocapsid protein (N) gene of TSWV was shown to be resistant to TSWV infection [Plant Sci. 164 (2003) 717]. In the present study, interactions between PVX engineered to contain the NSs gene sequences and TSWV were examined. Plants infected with PVX containing the NSs gene sequences showed a partial virus resistance to TSWV. However, the degree of the resistance was apparently lower than that observed in plants infected with PVX engineered to contain the N gene. Similar low levels of the resistance to TSWV was observed in plants infected with PVX engineered to contain the NSm gene of TSWV. These results suggest that RNA-mediated virus resistance conferred by the NSs and NSm gene sequences of TSWV was less effective to TSWV. Furthermore, it was also suggested that RNA-mediated virus resistance was affected by viral genes or sequences rather than the amount of nucleotide sequence homology.