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

Abstract

The plant-pathogenic virus, tomato spotted wilt virus (TSWV), encodes a structural glycoprotein (G_N) 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 that Frankliniella occidentalis is one of seven competent thrips vectors of TSWV transmission to plant hosts, however, the insect molecules that interact with viral proteins, such as G_N, 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 G_Nand 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 of F. occidentalis, the tissues most important during virus infection, replication and plant-inoculation. The TIPs and G_N interactions were validated using protein-protein interaction assays. Two of the thrips proteins, endocuticle structural glycoprotein and cyclophilin, were found to be consistent interactors with G_N. These newly discovered thrips protein-G_N interactions 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.