Abstract: Previously, we investigated the evolution of Potato mop-top
virus (PMTV) ORFs. More...
Abstract: Previously, we investigated the evolution of Potato mop-top
virus (PMTV) ORFs. Results indicate that positive selection acts
exclusively on an ORF encoding the 8K protein, a weak viral suppressor of
RNA silencing (VSR). However, how the extraordinary variability
contributes to 8K-mediated RNA silencing suppression remains unknown.
Here, we characterized the RNA silencing suppression activity of the 8K
protein from seven diverse isolates. We show that 8K encoded by isolate
P1 exhibits stronger RNA silencing suppression activity than the 8K
protein from six other isolates. Mutational analyses revealed that Ser-50
is critical for these differences. By comparing small RNA profiles we
found a lower abundance of siRNAs with U residue at the 5'-terminus after
expression of the P1 8K compared to expression of 8K from isolate P125,
an isolate with weak VSR activity. These results provide new clues as to
the role of positive selection in shaping activities of VSR Less...