LAUSR

Simple Summary Tomato spotted wilt virus (TSWV) is a plant virus that causes significant economic loss to high-valued crops, including hot pepper and tomato. It is transmitted by some thrips species, including Frankliniella occidentalis. Thrips obtain TSWV by feeding on infected host plants. The TSWV infects the midgut and then enters the thrips bodies, where the virus translocates to salivary glands for subsequent transmission. Here we assessed the actions of two intestinal proteins, glycoprotein (Fo-GN) and cyclophilin (Fo-Cyp1) in their functional association with TSWV infection of the midgut. Silencing the two genes encoding these two proteins led to a near-zero reduction of TSWV in midguts and salivary glands of the infected thrips. We propose that the two intestinal proteins, Fo-GN and Fo-Cyp1, are TSWV entry targets that are necessary to infect F. occidentalis for continued transmission to additional host plants. Abstract Tomato spotted wilt virus (TSWV) is a plant virus that causes massive economic damage to high-valued crops. This virus is transmitted by specific thrips, including the western flower thrips, Frankliniella occidentalis. TSWV is acquired by the young larvae during feeding on infected host plants. TSWV infects the gut epithelium through hypothetical receptor(s) and multiplies within the cells for subsequent horizontal transmission to other plant hosts via the salivary glands during feeding. Two alimentary canal proteins, glycoprotein (Fo-GN) and cyclophilin (Fo-Cyp1), are thought to be associated with the TSWV entry into the gut epithelium of F. occidentalis. Fo-GN possesses a chitin-binding domain, and its transcript was localized on the larval gut epithelium by fluorescence in situ hybridization (FISH) analysis. Phylogenetic analysis indicated that F. occidentalis encodes six cyclophilins, in which Fo-Cyp1 is closely related to a human cyclophilin A, an immune modulator. The Fo-Cyp1 transcript was also detected in the larval gut epithelium. Expression of these two genes was suppressed by feeding their cognate RNA interference (RNAi) to young larvae. The RNAi efficiencies were confirmed by the disappearance of the target gene transcripts from the gut epithelium by FISH analyses. The RNAi treatments directed to Fo-GN or Fo-Cyp1 prevented the typical TSWV titer increase after the virus feeding, compared to control RNAi treatment. Our immunofluorescence assay using a specific antibody to TSWV documented the reduction of TSWV in the larval gut and adult salivary gland after the RNAi treatments. These results support our hypothesis that the candidate proteins Fo-GN and Fo-Cyp1 act in TSWV entry and multiplication in F. occidentalis.