CHARACTERIZATION OF RNA-MEDIATED RESISTANCE TO TOMATO SPOTTED WILT VIRUS IN TRANSGENIC TOBACCO PLANTS EXPRESSING NSM GENE-SEQUENCES

Transgenic Nicotiana tabacum plants expressing RNA sequences of the to mato spotted wilt virus NSM gene, which encodes the putative viral mov ement protein, were found to be highly resistant to infection with the virus. Expression of untranslatable as well as anti-sense RNA of the NSM gene resulted in resistance levels as high as those in plants expr essing translatable RNA sequences. For all three types of transgenic p lants resistance levels of up to 100% were reached in the S2 progeny. These results indicate that the resistance mediated by the NSM gene is accomplished by expression of transcripts rather than protein in tran sgenic plants, similar to previously observed N gene-mediated resistan ce. Protoplast inoculations revealed that resistant plants expressing NSM are, in contrast to N transgenic resistant plants, not resistant a t the cellular level. This suggests the RNA-mediated resistance mechan ism against TSWV targets viral mRNAs rather than the viral genome.