Olive Mild Mosaic Virus Coat Protein and P6 Are Suppressors of RNA Silencing, and Their Silencing Confers Resistance against OMMV.

RNA silencing is an important defense mechanism in plants, yet several plant viruses encode proteins that suppress this mechanism. In this study, the genome of the (OMMV) was screened for silencing suppressors. The full OMMV cDNA and 5 OMMV open reading frames (ORFs) were cloned into the Gateway binary vector pK7WG2, transformed into , and agroinfiltrated into 16C plants. and showed suppressor activity, with showing significantly higher activity than , yet activity that was lower than the full OMMV, suggesting a complementary action of and . These viral suppressors were then used to induce OMMV resistance in plants based on RNA silencing. Two hairpin constructs targeting each suppressor were agroinfiltrated in plants, which were then inoculated with OMMV RNA. When silencing of both suppressors was achieved, a significant reduction in viral accumulation and symptom attenuation was observed as compared to those of the controls, as well as to when each construct was used alone, proving them to be effective against OMMV infection. This is the first time that a silencing suppressor was found in a necrovirus, and that two independent proteins act as silencing suppressors in a virus member of the family.