A method for Evaluation of RNA Silencing Suppression Activity in Plants Using two Proteins of Grapevine Fanleaf Virus

Suppressor proteins of RNA Silencing have been well described in most genera of plant viruses. The methodogy for identifying gene silencing suppressor activity of a protein in a plant system has proven to be an important tool. Grapevine fanleaf virus (GFLV) is one of the most common viral diseases in grapevines worldwide and can cause up to 80% crop losses. GFLV is a bipartite member of the Nepovirus subgroup A in the family Secoviridae and has a single-stranded positive-sense RNA genome. A viral suppressor of RNA silencing (VSR) in Nepoviruses has not yet been described and our knowledge of symptom determinant genes in nepeoviruses is very limited. In this study, a transgenic GFP gene was silenced in transgenic Nicotiana benthamiana line 16c, and then the ability of GFLV polymerase and movement proteins to suppress gene silencing was evaluated. The efficiency of these two proteins was compared with positive and negative controls. The results showed that neither protein had the ability to suppress gene silencing. However, these proteins are involved in symptom production and systemic infection. This study demonstrates a model method for evaluation of suppressor activity of RNA Silencing.