Polerovirus protein P0 prevents the de novo assembly of siRNA/miRNA-containing ARGONAUTE1 complexes, ultimately leading to AGO1 degradation without affecting pre-programmed RISC slicer activity.
The poleroviral P0 protein suppresses plant antiviral RNA silencing by preventing the assembly of the RISC complex and promoting AGO1 degradation.
RNA silencing plays an important role in plants in defence against viruses. To overcome this defence, plant viruses encode suppressors of RNA silencing. The most common mode of silencing suppression is sequestration of double-stranded RNAs involved in the antiviral silencing pathways. Viral suppressors can also overcome silencing responses through protein-protein interaction. The poleroviral P0 silencing suppressor protein targets ARGONAUTE (AGO) proteins for degradation. AGO proteins are the core component of the RNA-induced silencing complex (RISC). We found that P0 does not interfere with the slicer activity of pre-programmed siRNA/miRNA containing AGO1, but prevents de novo formation of siRNA/miRNA containing AGO1. We show that the AGO1 protein is part of a high-molecular-weight complex, suggesting the existence of a multi-protein RISC in plants. We propose that P0 prevents RISC assembly by interacting with one of its protein components, thus inhibiting formation of siRNA/miRNA-RISC, and ultimately leading to AGO1 degradation. Our findings also suggest that siRNAs enhance the stability of co-expressed AGO1 in both the presence and absence of P0.
Csorba et al. (2010) studied Plant viral infection and RNA silencing. Polerovirus protein P0 was evaluated on ARGONAUTE1 degradation and RISC assembly. Polerovirus protein P0 prevents the de novo assembly of siRNA/miRNA-containing ARGONAUTE1 complexes, ultimately leading to AGO1 degradation without affecting pre-programmed RISC slicer activity.