Systematic Mutagenesis Analysis of the Turnip yellows virus Suppressor of RNA Silencing P0 
M. SACCO (1), T. Nguyen (1), M. Dughbaj (1), K. Valdez (1), S. Oza (1), T. Choi (1), K. Wang (1) (1) California State University, Fullerton, U.S.A.

The Polerovirus genus includes plus-sense RNA viruses transmitted by aphids with broad host ranges. The protein P0 is the Polerovirus viral suppressor of RNA silencing (VSR), which causes degradation of Argonaute (AGO) proteins. The P0 protein from Turnip yellows virus (TuYV; P0Tu) is recognized in Nicotiana glutinosa leading to TuYV resistance and the hypersensitive response (HR).  We are interested in understanding how P0Tu acts as a VSR in susceptible plants versus an elicitor of HR in resistant plants. To identify important amino acids, P0Tu was subjected to serial deletion and site-directed mutagenesis at either several conserved sites or by systematic substitutions with the 6 amino acid sequence NAAIRS along the entire coding sequence. We predicted that the modifications could potentially cause loss of VSR activity in Nicotiana benthamiana and/or loss of HR elicitation in N. glutinosa to dissect these two functions. Mutant clones were co-expressed with GFP in N. glutinosa and N. benthamiana to observe for VSR activity and induction of cell death. Amino acids at the N-terminus were important for all P0Tu functions, while the last 22 C-terminal amino acid residues (227-249) were important for HR elicitation but not VSR activity. Substitution of two conserved central arginine residues with lysine caused P0Tu to elicit more robust HRs on N. glutinosa.  Our results show that P0Tu activities in suppression of RNA silencing and elicitation of HR involve both overlapping and unique regions of the protein, and VSR activity of P0Tu is insufficient to trigger HR in N. glutinosa.

Abstract Number: P17-599
Session Type: Poster