Abstract
Plant viruses are inducers and targets of antiviral RNA silencing. To condition susceptibility, most plant viruses encode silencing suppressor proteins that interfere with antiviral RNA silencing. The NSs protein is an RNA silencing suppressor in orthotospoviruses, such as the tomato spotted wilt virus (TSWV). The mechanism of RNA silencing suppression by NSs and its role in virus infection and movement are poorly understood. Here, we cloned and tagged TSWV NSs and expressed it from a GFP-tagged turnip mosaic virus (TuMV-GFP) carrying either a wild-type or suppressor-deficient (AS9) helper component proteinase (HC-Pro). When expressed in cis, NSs restored pathogenicity and promoted systemic infection of suppressor-deficient TuMV-AS9-GFP in Nicotiana benthamiana and Arabidopsis thaliana. Inactivating mutations were introduced in NSs RNA-binding domain one. A genetic analysis with active and suppressor-deficient NSs, in combination with wild-type and mutant plants lacking essential components of the RNA silencing machinery, showed that the NSs insert is stable when expressed from a potyvirus. NSs can functionally replace potyviral HC-Pro, condition virus susceptibility, and promote systemic infection and symptom development by suppressing antiviral RNA silencing through a mechanism that partially overlaps that of potyviral HC-Pro. The results presented provide new insight into the mechanism of silencing suppression by NSs and its effect on virus infection.
Highlights
RNA silencing contributes to the regulation of gene expression and the maintenance of genome integrity in eukaryotes
At 4 days post infiltration, pictures were taken under UV light and GFP fluorescence was estimated using the green channel in GKT motif and the YL motif are necessary for transgene silencing suppression [44]
The results described above showed that tomato spotted wilt virus (TSWV) NSs is an RNA silencing suppressor that promotes systemic virus movement and symptom development (Figures 2 and 4)
Summary
RNA silencing contributes to the regulation of gene expression and the maintenance of genome integrity in eukaryotes. Nematodes, and insects, gene silencing is an inducible, adaptable, specific, potent, and essential defense system against virus infection (antiviral RNA silencing) [1,2,3,4,5,6,7]. Both endogenous and antiviral RNA silencing initiate with the processing of double-stranded RNA by Dicer-like (DCL) proteins to form small RNAs of 21 to 24 nt that associate with. Restriction of plant virus infection requires silencing amplification by cellular RNA-dependent RNA polymerases (RDR) to establish an antiviral state [3,9,10].
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