Virus and RNA Silencing

The poleroviruses are an agronomically important genus of plant viruses which can infect a wide range of hosts. Their genome is a single-stranded plus-sense RNA. The 5'-terminal ORF encodes the 29 kDa protein P0, a strong suppressor of Post- Transcriptional Gene Silencing (PTGS), an important antiviral defense system in plants. I have investigated the mechanism of action of P0 in suppression of RNA silencing. Our data support a model in which P0 acts as an F-box protein, recruiting the post-translational modification system to overcome the post-transcriptional gene silencing system. In this model P0 interacts with SKP to constitute a SCFP0 complex which presumably addresses ARGONAUTE1 that is the slicer protein in the RNA-induced silencing complex (RISC), for ubiquitination and degradation by 26S proteasome. This would be the first example of a suppressor of RNA silencing that acts in an SCF complex to promote degradation of an essential component of the silencing pathway, thereby, inhibiting the plant antiviral defense.