The divergent V2 protein encoded by parsley yellow leaf curl virus is a suppressor of transcriptional and post-transcriptional gene silencing and a potential symptom determinant
TL;DR
It is demonstrated that the divergent V2 protein from PYLCV has the capacity to function as a viral suppressor of RNA silencing (VSR) and as a potential symptom determinant, suggesting relevant roles in viral pathogenicity analogous to those of other geminiviral V2 proteins.
Abstract
The Geminiviridae family encompasses over 500 species of economically important plant viruses. A new geminivirus species named parsley yellow leaf curl virus (PYLCV) was first identified in 2020 in Southeastern Iran. The PYLCV genome, comprising 2,779 nucleotides, exhibits a pairwise sequence identity of less than 66% with other geminiviruses and encodes a divergent V2 protein that lacks sequence similarity to known proteins in GenBank. This study explores the functions of this V2 through various analyses. An assessment of the V2 amino acid composition indicates a higher prevalence of acidic residues. By expressing N-terminal and C-terminal GFP fusions (GFP-V2 and V2-GFP) in Nicotiana benthamiana, we demonstrate that V2 localizes to the cytoplasm, nucleus, endoplasmic reticulum, and the Cajal body. Notably, PYLCV V2 suppressed local PTGS and delayed systemic PTGS in GFP-based silencing assays and restored GFP transcript accumulation in a systemic 16c-TGS assay, indicating suppression of transcriptional silencing. Co-immunoprecipitation assays further showed that PYLCV V2 interacts with NbAGO4-1 and with itself, but not detectably with NbSGS3 or NbHDA6, supporting a potential role for PYLCV V2 in targeting the AGO4-mediated transcriptional silencing pathway. Ectopic expression of V2 via a PVX vector induced necrotic lesions with HR-like features, together with systemic mosaic patterns and severe leaf curling in upper leaves. Importantly, PYLCV V2 retains core V2-like biological activities despite extensive primary-sequence divergence, suggesting that functional conservation may rely on structural or biophysical determinants rather than linear sequence similarity. Our findings demonstrate that the divergent V2 protein from PYLCV has the capacity to function as a viral suppressor of RNA silencing (VSR) and as a potential symptom determinant, suggesting relevant roles in viral pathogenicity analogous to those of other geminiviral V2 proteins.