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Characterization of two biologically distinct variants of Tomato spotted wilt virus

Raphael Adegbola: Washington State University

<div><em>Tomato spotted wilt virus</em> (TSWV, genus: <em>Orthotospovirus</em>; family: <em>Tospoviridae</em>) causes significant economic losses to a wide range of crops. In this study, one TSWV isolate from basil (TSWV-C) and a second isolate from tomato (TSWV-Wa1) were established in <em>Emilia sonchifolia</em>. Time-course analysis of inoculated <em>E. sonchifolia</em> plants by ELISA using G<sub>N</sub>-, G<sub>C</sub>- and NSs-specific antibodies revealed similar amounts of the G<sub>N</sub> and G<sub>C</sub> glycoproteins present in plants infected with TSWV-C and TSWV-Wa1 isolates, but higher amounts of NSs in TSWV-C-infected plants. In host range studies, the two isolates showed distinct phenotypic differences with TSWV-C producing severe symptoms on several permissible hosts compared to TSWV-Wa1 that showed limited host range. TSWV-C caused systemic infection with severe symptoms in a susceptible tomato cultivar compared to TSWV-Wa1 that was found to be largely localized to inoculated leaves. The S-, M-, and L-RNA sequences of the two distinct isolates, generated using a combination of Sanger sequencing and high-throughput sequencing, showed 96.6 to 97.9% identity at the nucleotide level. Among the different ORFs, the NSs gene was more divergent, with 97.0% identity at the amino acid level. In agroinfiltration assays, the TSWV-Wa1 NSs protein showed weaker RNA silencing suppression (RSS) activity than the TSWV-C NSs protein. Specific amino acid substitutions were found responsible for the observed weak RSS activity of the TSWV-Wa1 NSs protein.</div>