Figure 2.

The balance between gene silencing and silencing suppression determines infection progression. Arabidopsis thaliana plants were mechanically inoculated with suppressor‐deficient turnip mosaic virus (TuMV)‐GFP or TuMV‐GFP. In Nicotiana benthamiana plants, infection was initiated by agroinfiltration. Pictures were taken under UV light. (A) In A. thaliana, Dicer‐like proteins 2 and 4 (DCL2 and DCL4) are core components of antiviral gene silencing and restrict virus infection in a tissue‐specific manner. In leaves, DCL4 is sufficient and DCL2 is dispensable. In the inflorescence, both DCL2 and DCL4 are necessary to restrict virus infection. TuMV‐encoded silencing suppressor (HC‐Pro) overcomes the antiviral effect of gene silencing and promotes the establishment of infection in leaves and the inflorescence. (B) In N. bethamiana RDR6 is an essential component of gene silencing. Suppressor‐deficient TuMV‐AS9‐GFP cannot infect wild‐type N. benthamiana. Local and systemic infection occurred by knocking down RDR6 in rdr6i plants, or by providing in cis the silencing suppressor from tomato spotted wilt virus. In normal and rd6i plants, local and systemic infection occur and the virus accumulates to high levels. Pathogenicity is determined by TuMV HC‐Pro.