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Vector Relations

Tospovirus Replication in Insect Vector Cells: Immunocytochemical Evidence that the Nonstructural Protein Encoded by the S RNA of Tomato Spotted Wilt Tospovirus Is Present in Thrips Vector Cells. Diane E. Ullman,Department of Entomology, University of Hawaii, 3050 Maile Way, Rm 310, Honolulu, 96822; Thomas L. German(2), John L. Sherwood(3), Daphne M. Westcot(4), and Frank A. Cantone(5). (2)Department of Plant Pathology, University of Wisconsin, Russell Laboratories, 1630 Linden Dr., Madison, 53706; (3)Department of Plant Pathology, Oklahoma State University, Stillwater, 74078; (4)Department of Entomology, University of Hawaii, 3050 Maile Way, Rm 310, Honolulu, 96822; (5)Present address: Boyce Thompson Institute, Cornell University, Ithaca, NY 14853. Phytopathology 83:456-463. Accepted for publication 4 November 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-456.

Tomato spotted wilt tospovirus (TSWV) is an insect-transmitted virus that is the type member of the Tospovirus genus, which is the only genus in the family Bunyaviridae containing viruses that infect plants. Direct evidence that Tospoviruses replicate in their thrips vectors has been difficult to obtain because of limitations to definitively detect replicative intermediates of TSWV or to immunolabel vector tissues. A nonstructural protein is encoded by the small RNA of TSWV, and translation of the NSs protein occurs from a subgenomic RNA formed after transcription of viral sense RNA. This protein is designated as nonstructural because it is found only in TSWV-infected cells and has not been found in assembled virions. Thus, presence of NSs indicates that processes of virus replication have occurred. A specific and sensitive antibody to the NSs has been produced and used to localize NSs in the cells of a thrips vector species, Frankliniella occidentalis. The direct, immunocytochemical evidence presented that NSs is present in thrips cells indicates that TSWV, a plant pathogenic virus, replicates in the cells of its invertebrate vector. Replication of TSWV in thrips cells is significant to understanding the pandemic importance and taxonomy of this virus.