Date Published: September 26, 2018
Publisher: Public Library of Science
Author(s): Haoyang Li, Bin Yin, Sheng Wang, Qihui Fu, Bang Xiao, Kai Lǚ, Jianguo He, Chaozheng Li, Kui Li.
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 to inhibit viral infection. Taken together, we therefore identify that the Toll4-Dorsal pathway mediates strong resistance to WSSV infection by inducing some specific AMPs.
Multicellular organisms have evolved for the ability to protect themselves from a wide variety of pathogens such as viruses. In invertebrates including shrimps that lacking immunoglobulin-based adaptive immune system, this protection is thus provided through the action of an innate immune system. The innate immune response is generally initiated via the detection of pathogen-associated molecular patterns (PAMPs), some evolutionarily conserved structures or motifs shared by broad classes of invading organisms, by a wide diversity of host pattern recognition receptors (PRRs) . One important class of PRRs is the Toll receptor superfamily, comprising invertebrate Tolls and vertebrate Toll-like receptors (TLRs), and is now considered to be the primary sensor of pathogens in all metazoans .
Accumulating evidence indicates that shrimp Tolls participate in host defense against WSSV infection; however, the underlying mechanism of the Toll receptor mediated antiviral functions has been poorly understood. Herein, we have identified an antiviral role for a new Toll from L. vannamei, the Toll4, in response to WSSV infection in vivo. Toll4 silenced shrimps demonstrate significantly elevated viral replication and mortality after WSSV challenge. Shrimps with knockdown of genes in some core components of the canonical Toll pathway such as MyD88, Tube, Pelle and Dorsal have remarkably increased WSSV titers. Furthermore, Toll4 appears to be specific to sense WSSV infection to trigger Dorsal, which lead to induce a specific set of AMPs with the ability of interacting with viral structural proteins that confer resistance to viral infection. Our results have now demonstrated that the Toll4-Dorsal-AMPs cascade is involved in the control of WSSV infection in shrimp.