ABSTRACT
The function of Toll pathway defense against bacterial infection has been well established in shrimp, however how this pathway responds to viral infection is still largely unknown. In this study, we report the Toll4-Dorsal-AMPs cascade restricts the white spot syndrome virus (WSSV) infection of shrimp. A total of nine Tolls from Litopenaeus vannamei namely Toll1-9 are identified, and RNAi screening in vivo reveals the Toll4 is important for shrimp to oppose WSSV infection. Knockdown of Toll4 results in elevated viral loads and renders shrimp more susceptible to WSSV. Furthermore, Toll4 could be a one of upstream pattern recognition receptor (PRR) to detect WSSV, and thereby leading to nuclear translocation and phosphorylation of Dorsal, the known NF-κB transcription factor of the canonical Toll pathway. More importantly, silencing of Toll4 and Dorsal contributes to impaired expression of a specific set of antimicrobial peptides (AMPs) such as anti-LPS-factor (ALF) and lysozyme (LYZ) family, which exert potent anti-WSSV activity. Two AMPs of ALF1 and LYZ1 as representatives are demonstrated to have the ability to interact with several WSSV structural proteins. Taken together, we therefore identify the Toll4-Dorsal pathway mediates strong resistance to WSSV infection by inducing some specific AMPs.
Author summary The TLR pathway mediated antiviral immune response is well identified in mammals, yet, Toll pathway governing this protection in invertebrates remains unknown. In the present study, we uncover that a shrimp Toll4 from a total of nine Tolls in L. vannamei confers resistance to WSSV thought inducing the NF-κB transcription factor Dorsal to inspiring the production of some antimicrobial peptides (AMPs) with antiviral activity. The anti-LPS-factor (ALF) and lysozyme (LYZ) family are identified as the Toll4-Dorsal pathway targeted genes with the ability to interact with viral structural proteins in response to WSSV infection. These results suggest that the Toll receptor induces the expression of AMPs with antiviral activity could be a general antiviral mechanism in invertebrates and Toll pathway established antiviral defense could be conserved during evolution.
