Cucurbit yellow stunting disorder virus p25 is a suppressor of post-transcriptional gene silencing

Abstract

Post-transcriptional gene silencing (PTGS) degrades RNA in a sequence-specific manner and is utilised by plants as a natural defence mechanism against virus invaders. Two members of the genus Crinivirus have been reported to encode suppressors and counter PTGS: Sweet potato chlorotic stunt virus p22 and Tomato chlorosis virus (ToCV) p22, coat protein and coat protein minor. Using an Agrobacterium-mediated transient assay on Nicotiana benthamiana wildtype and 16c plants, we screened four Cucurbit yellow stunting disorder virus (CYSDV) RNA 1-encoded proteins (papain-like protease, p25, p5.2 and p22) to determine which one possess PTGS suppressor activity. Amongst these proteins, only CYSDV p25 was able to suppress (double- and single-stranded) RNA-induced silencing of the green fluorescent protein (GFP) mRNA. Restoration of GFP expression by CYSDV p25 in both of these experiments had no apparent effect on the accumulation of the small interfering RNAs. The identification of CYSDV p25 adds to the list of suppressors encoded by crinivirus RNA 1 molecules, which are unrelated in terms of amino acid sequence homology suggesting distinct PTGS suppression mechanisms and possible roles in viral replication.