Drosophila melanogasterToll-9 elicits antiviral immunity againstDrosophilaC virus

Abstract

The Toll pathway plays a pivotal role in innate immune responses against pathogens. The evolutionary conserved pathogen recognition receptors (PRRs), including Toll like receptors (TLRs), play a crucial role in recognition of pathogen associated molecular patterns (PAMPs). TheDrosophilagenome encodes nine Toll receptors that are orthologous to mammalian TLRs. While mammalian TLRs directly recognize PAMPs, mostDrosophilaTolls recognize the proteolytically cleaved ligand Spätzle to activate downstream signaling cascades. In this study, we demonstrated that Toll-9 is crucial for antiviral immunity againstDrosophilaC virus (DCV), a natural pathogen ofDrosophila. A transposable element insertion in theToll-9gene renders the flies more susceptible to DCV. The stable expression of Toll-9 in S2 cells confers resistance against DCV infection by upregulation of the RNAi pathway. Toll-9 promotes the dephosphorylation of AKT, resulting in the induction of antiviral RNAi genes to inhibit DCV replication. Toll-9 localizes to the endosome where it binds dsRNA, suggesting its role to detect viral dsRNA. Toll-9 also induces apoptosis during DCV infection, contributing to its antiviral role. Together, this work identifies the role of Toll-9 in antiviral immunity against DCV infection through its ability to bind dsRNA and induce AKT-mediated RNAi antiviral immunity.IMPORTANCEInsects rely on innate immunity and RNA interference (RNAi) to combat viral infections. Our study underscores the pivotal role ofDrosophilaToll-9 in antiviral immunity, aligning with findings inBombyx mori, where Toll-9 activation upregulates the RNAi componentDicer2. We demonstrate thatDrosophilaToll-9 functions as a pattern recognition receptor (PRR) for double-stranded RNA (dsRNA) duringDrosophila Cvirus (DCV) infection, akin to mammalian TLRs. Toll-9 activation leads to the upregulation of key RNAi components,Dicer2andArgonaute2, and dephosphorylation of AKT triggers apoptosis via induction of proapoptotic genesHidandReaper. This study also reveals that Toll-9 localizes in endosomal compartments where it interacts with dsRNA. These insights enhance our understanding ofDrosophilainnate immune mechanisms, reflecting the evolutionary conservation of immune responses across diverse species and providing impetus for further research into the conserved roles of TLRs across the animal kingdom.