The Study Of The Entomopathogenic Fungus Metarhizium Rileyi Against Innate Immunity Of Its Host Spodoptera Frugiperda

Metarhizium rileyi,an important entomopathogenic fungus,is widely distributed in the world,which has great application prospect.When M.rileyi infected the host insect,it adheres to the host cuticle as conidia,penetrates the insect body through mechanical stress and secreting proteases after germination.It can escape and inhibit the immune response of the insect to breeding and occupying the haemocoele of host.S.frugiperda is an invasive species in China in recent years,which causes serious damage and is difficult to control.It has found that M rileyi has strong virulence to infection S.frugiperda in some studies,but the mechanism is not clear.So,in our study,we study the mechanism on S.frugiperda innate immune response after M rileyi infection of the host insects,and the mechanism of M rileyi inhibition of S.frugiperda innate immune,the specific results are as follows:1.Virulence analysis of mutant strains.The 3rd larva of S.frugiperda were infected with the conidia of M rileyi.The survival rates were 0 and 10%at 1×109 个/mL and 1×108个/mL,were 40%and 70%at 1×107 个/mL and 1×106 个/mL after 10 d.It showed M.has strong virulence to infection S.frugiperda.2.Determine injection infection concentration.The 3rd larvae of S.frugiperda were injected with the blastospores of M.rileyi.According to the results,the injection infection concentration of 1×104 spores were selected for our experiments.3.The influence on cellular immune response.After M rileyi injection,the total number of hemocytes was significantly reduced,and the total number of granulocytes and plasmatocytes was also significantly reduced.The nodulation,encapsulation,and phagocytosis responses were significantly inhibited.The spreading of plasmatocyte was significantly inhibited.4.The influence on the cytoskeleton of hemocyte.The cytoskeleton of S.frugiperda hemocytes was dyeing with FITC-phalloidin,the results show that the cytoskeleton of S.frugiperda hemocytes is disorder after M rileyi infection,then the cellular immunity of S.frugiperda was completely inhibited.5.The influence on humoral immune response.M.rileyi infection had no effect on the prophenoloxidase activation.The hemolymph of S.frugiperda has obvious antibacterial activity against E.coli and S.aureus after M.rileyi infection.6.Transcriptome analysis and validation of the fat body.To further investigate the mechanism of immune response to M.rileyi,transcriptome sequencing was performed on the fat body of M.rileyi infected and uninfected.A total of 1771 DEGs were identified in the transcriptome,among which 468 genes were up-regulated and 325 genes were down-regulated in 12 h sample.In 48 h samples,574 genes were up-regulated and 484 genes were down-regulated.These genes were involved in many biological processes.A total 134 genes related to insect innate immunity were screened out,including 32 genes related to pattern recognition receptors;23 genes related to signaling pathway;27 genes related to antimicrobial peptide and other effector;53 genes related to prophenoloxidase activator pathway.18 DEGs were selected from innate immune genes,and their expression levels were detected and verified at the mRNA level.The qPCR results were consistent with transcriptome sequencing results.In conclusion,although the host insect can respond to the fungus,M.rileyi can inhibit the innate immune of the host after M.rileyi injected.These results deepen our understanding of the immune interaction between entomopathogenic fungi and host insects,and provide a theoretical basis for the future biological control of M rileyiagainst S.frugiperda.