The Toll pathway and Duox-ROS system are required for the clam antibacterial immune response in the hepatopancreas

Abstract

Vibriosis is one of the most important bacterial diseases that can cause mass mortality of mollusks, especially in summer, and has contributed to dramatic economic losses. Infection is the result of complex molecular interactions between the host and invading agents. Understanding the interaction mechanism could provide a scientific basis for disease control and genetic breeding of resistant varieties. In this paper, the clam Meretrix petechialis was challenged with Vibrio parahaemolyticus to simulate bacterial infection in the natural environment. The Vibrio load variation in the clam hepatopancreas was surveyed during the early phase of Vibrio infection (i.e., latency, prodrome), and the results showed that the Vibrio load was high at 1 dpi (days post-infection), and then dramatically decreased at 2 dpi and remained low at the following time points. The key genes in Toll pathway and the reactive oxygen species (ROS) system were activated to release antibacterial peptide (AMP) and H2O2 during early bacterial infection, respectively. An RNAi experiment further supported that the Toll pathway and ROS system could directly control Vibrio abundance by producing AMP and H2O2. This study provides novel insights into the identity of host factors that enhance or restrict pathogenesis.