Comparing p20’s RNA silencing suppressing activity among five phylogenetic groups of Citrus Tristeza virus

Abstract

The p20 protein encoded by the Citrus Tristeza Virus (CTV) was previously identified as a RNA silencing suppressor. In this study, we analyzed the p20's suppressing activity from five phylogenetic groups of CTV, using the co-infiltration assay of Green fluorescence protein (GFP) gene and the suppressor gene in 16C line Nicotiana benthamiana plants. Green fluorescence, GFP mRNA relative levels and GFP specific siRNAS were compared showing in most cases, only slight differences. Contrary to previous studies, the p20 suppressor was not able to impede neither short range nor systemic spreading of RNA silencing. The suppressor from the phylogenetic group 4 revealed a much reduced activity when compared with the others. At present we still don't know whether this property is a characteristic of this group or an atypical feature due to a unique point mutation. The differences in the symptom type and intensity originated by isolates belonging to the phylogenetic groups assayed could not be related to differences to the p20 suppressor's activity.

Key Importance of Small RNA Binding for the Activity of a Glycine-Tryptophan (GW) Motif-containing Viral Suppressor of RNA Silencing

“…VSRs are very diverse in sequence and additional function(s), and no correlation among VSR types and viral phylogeny can be established (25). Moreover, differences in VSR activity have been found among viruses of the same genus (26 -28) or even among isolates of the same virus species (29,30). Although many questions remain to be answered, the growing knowledge about the mechanism of action of several VSRs reveals that virtually all stages of the antiviral silencing pathway can be targeted by these viral products and that a given VSR may inhibit or inactivate one or more components of the silencing machinery (31,32).…”