Groundnut bud necrosis virus induces necrotic symptoms in different hosts. Previous studies showed reactive oxygen species-mediated programmed cell death (PCD) resulted in necrotic symptoms. Transgenic expression of viral protein NSs mimics viral symptoms. Here, we showed a role for NSs in influencing oxidative burst in the cell, by analyzing H2O2 accumulation, activities of antioxidant enzymes and expression levels of vacuolar processing enzymes, H2O2-responsive microRNA 319a.2 plus its possible target metacaspase-8. The role of NSs in PCD, was shown using two NSs mutants: one in the Trp/GH3 motif (a homologue of pro-apototic domain) (NSsS189R) and the other in a non-Trp/GH3 motif (NSsL172R). Tobacco rattle virus (TRV) expressing NSsS189R enhanced the PCD response, but not TRV-NSsL172R, while RNA silencing suppression activity was lost in TRV-NSsL172R, but not in TRV-NSsS189R. Therefore, we propose dual roles of NSs in RNA silencing suppression and induction of cell death, controlled by different motifs.
Keywords: MicroRNA; Reaper; Trp/GH3 motif; Vacuolar processing enzyme.
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