Multi-Omics-Based Dissections On The Immune Response Of Rhynchophorus Ferrugineus Olivier During Exposure To Different Pathogens

Red palm weevil(RPW),Rhynchophorus ferrugineus Olivier,is a tremendously destructive insect pest of palm trees worldwide.Although some chemical insecticides and biological agents have been used to fight against RPW larvae,the control efficiency is still dissatisfactory.Insect immunity is vital for fighting against pathogens.Therefore,the elucidation of the mechanism underlying insect immunity can provide important insights for the development of some new pesticides,such as insect immunity inhibitors.This study aimed to determine the mechanism underlying how the immune system of RPW is activated during exposure to different pathogens by comparative genomic analysis,transcriptomics,proteomics and RNAi.Based on the published genome data of RPW,we found that there are 155 immune-related genes in the genome of this pest,including 55 pattern recognition receptor genes from five families,such as PGRP,GNBP,CTL,Tep and FREP,38 genes encoding immune signal transduction factors,40 genes encoding immune regulators and 22 genes encoding immune effectors.This study has shown that the immune system of RPW is similar to that of known model insects,and it is mainly composed of pattern recognition receptors,three immune signaling pathways(Toll,Imd and JAK-STAT),prophenoloxidase cascade and immune effectors.Transcriptomics and proteomics sequencing analysis confirmed that Imd pathway is the pivotal signaling pathway to regulate the immune response of RPW against Escherichia coli,while Toll pathway is the main signaling pathway to mediate the immune response of this pest against Staphyloccocus aureus and Beauveria bassiana.Prophenoloxidase cascade is the common strategy for RPW to against three different pathogens.Transcriptomics analysis showed that the challenge with different pathogens could significantly induce the expression of RfGNBP5,suggesting that RfGNBP5 may play a vital role in the immune defense of RPW.RfGNBP5 is a secreted protein with two conservative amino acid residues,being essential for hydrolysis activity,implying that it can degrade pathogen-associated molecular patterns(PAMPs).The abundance of RfGNBP5 transcripts in the hemolymph was significantly higher than that in other tissues.After RfGNBP5 was silenced,RT-q PCR revealed that the expression levels of Rf Attacin,Rf Coleoptericin,Rf PPO2 and Rf PPO3,and the activity of phenoloxidase were significantly enhanced.Furthermore,silencing RfGNBP5 dramatically enhanced the ability of individuals to clear the pathogenic bacteria and fungi.Taken together,these results demonstrated that RfGNBP5 acts as a negative regulator to maintain immune homeostasis of this pest.