Negative-Strand Tospoviruses and Tenuiviruses Carry a Gene for a Suppressor of Gene Silencing at Analogous Genomic Positions

Abstract

ABSTRACT Posttranscriptional silencing of a green fluorescent protein (GFP) transgene in Nicotiana benthamiana plants was suppressed when these plants were infected with Tomato spotted wilt virus (TSWV), a plant-infecting member of the Bunyaviridae . Infection with TSWV resulted in complete reactivation of GFP expression, similar to the case for Potato virus Y , but distinct from that for Cucumber mosaic virus , two viruses known to carry genes encoding silencing suppressor proteins. Agrobacterium -based leaf injections with individual TSWV genes identified the NS S gene to be responsible for the RNA silencing-suppressing activity displayed by this virus. The absence of short interfering RNAs in NS S -expressing leaf sectors suggests that the tospoviral NS S protein interferes with the intrinsic RNA silencing present in plants. Suppression of RNA silencing was also observed when the NS3 protein of the Rice hoja blanca tenuivirus , a nonenveloped negative-strand virus, was expressed. These results indicate that plant-infecting negative-strand RNA viruses carry a gene for a suppressor of RNA silencing.