Discovery of novel thrips vector proteins that bind to the viral attachment protein of the plant bunyavirus, tomato spotted wilt virus

The plant-pathogenic virus, tomato spotted wilt virus (TSWV), encodes a structural glycoprotein (GN) that, like with other bunyavirus/vector interactions, serves a role in viral attachment and possibly entry into arthropod vector host cells. It is well documented thatFrankliniella occidentalisis one of seven competent thrips vectors of TSWV transmission to plant hosts, however, the insect molecules that interact with viral proteins, such as GN, during infection and dissemination in thrips vector tissues are unknown. The goals of this project were to identify TSWV-interacting proteins (TIPs) that interact directly with TSWV GNand to localize expression of these proteins in relation to virus in thrips tissues of principle importance along the route of dissemination. We report here the identification of six TIPs from first instar larvae (L1), the most acquisition-efficient developmental stage of the thrips vector. Sequence analyses of these TIPs revealed homology to proteins associated with the infection cycle of other vector-borne viruses. Immunolocalization of the TIPs in L1s revealed robust expression in the midgut and salivary glands ofF. occidentalis, the tissues most important during virus infection, replication and plant-inoculation. The TIPs and GNinteractions were validated using protein-protein interaction assays. Two of the thrips proteins, endocuticle structural glycoprotein and cyclophilin, were found to be consistent interactors with GN. These newly discovered thrips protein-GNinteractions are essential towards better understanding of transmission of persistent propagative plant viruses by their vectors, as well as for developing new strategies of insect pest management and virus resistance in plants.Importance StatementThrips-transmitted viruses cause devastating losses to numerous food crops worldwide. For negative-sense RNA viruses that infect plants, the arthropod serves as a host as well by supporting virus replication in specific tissues and organs of the vector. The goal of this work was to identify vector/host proteins that bind directly to the viral attachment protein and thus may play a role in the infection cycle in the insect. Using the model plant bunyavirus, tomato spotted wilt virus (TSWV), and the most efficient thrips vector, we identified and validated six TSWV-interacting proteins fromFrankliniella occidentalisfirst instar larvae. Two proteins, an endocuticle structural glycoprotein and cyclophilin, were able to interact directly with the TSWV attachment protein, GN, in insect cells. The TSWV GN-interacting proteins provide new targets for disrupting the virus-vector interaction and could be putative determinants of vector competence.