Systematic mutagenesis of Polerovirus protein P0 reveals distinct and overlapping amino acid functions in Nicotiana glutinosa.

The protein P0 serves as the viral suppressor of RNA silencing (VSR) for poleroviruses, but elicits the hypersensitive response (HR) in specific Nicotiana species. We subjected P0 proteins from turnip yellows virus (P0) and potato leafroll virus (P0) to serial deletion and performed extensive site-directed mutagenesis of P0. Most deletions of the N-terminus and many substitution mutations disrupted both HR elicitation and VSR activity.