In transgenic and nontransgenic plants, viruses are both initiators and targets of a defense mechanism that is similar to posttranscriptional gene silencing (PTGS). Recently, it was found that potyviruses and cucumoviruses encode pathogenicity determinants that suppress this defense mechanism. Here, we test diverse virus types for the ability to suppress PTGS. Nicotiana benthamiana exhibiting P...

RNA 1 of the V strain of tomato aspermy virus (TAV) consists of 3410 nucleotides and contains one open reading frame (ORF) of 2982 nucleotides, resembling RNA 1 of cucumber mosaic virus (CMV) strains Q and Fny (68% and 66% identical, respectively) and of brome mosaic virus (BMV) (41% identical). In comparisons between amino acid sequences, three conserved regions (N-terminal, C-terminal and cen...

Plant and animal viruses encode suppressor proteins of an adaptive immunity mechanism in which viral double-stranded RNA is processed into 21-25 nt short interfering (si)RNAs. The siRNAs guide ARGONAUTE (AGO) proteins so that they target viral RNA. Most viral suppressors bind long dsRNA or siRNAs and thereby prevent production of siRNA or binding of siRNA to AGO. The one exception is the 2b sup...