Possible correlation of selected immune genes of tiger shrimp, Penaeus monodon with respect to white spot syndrome virus (WSSV) infection

Abstract White spot syndrome virus (WSSV) of shrimp is a highly virulent pathogen, which can bring mass mortality and thereby severe economic loss to the industry. Though shrimp has a less developed immune system, several gene components have been discovered which play certain and specific roles. Defense response of shrimp with respect to particular pathogen such as WSSV needs to be understood. The current study investigated the physiological changes and gene expression pattern with respect to silencing of Relish, IAP or Rab7 in Penaeus monodon by gene specific dsRNA followed by flow cytometry analysis after WSSV infection. RNAi has been used as a powerful tool to analyze the gene function in worms, shrimps, insects and plants. Knockdown of specific defense genes by dsRNA treatment and functional pattern of other intact genes were observed through expression analysis and flow cytometry. Penaeus monodon signal transducer and activator of transcription (PmSTAT) gene expression was found to be up regulated in case of dsRNA knocked down of either Penaeus monodon Relish transcription factor (PmRelish), inhibitor of apoptosis (IAP) explaining important role of STAT in immunity. Crustin expression was significantly down regulated in dsIAP and dsRelish injected animal. PmRelish and Crustin expression was up regulated in Rab7 silenced P. monodon. Necrosis and early apoptosis were high in PmRelish silenced P. monodon suggesting possible role of PmRelish in apoptosis pathway. Similarly, individual dsRNA silenced shrimp cells showed distinct phenotypic changes. The study indicates distinct inter-relationship between different defense genes while acting synergistically to provide overall protection against shrimp WSSV.