Studies On The Mechanism By Which Nomuraea Rileyi Suppresses The Immune Responses Of Its Host Helicoverpa Armigera

The entomopathogenic fungus Nomuraea rileyi is infectious to various lepidopteran pests,especially noctuids.The study on the mechanism of inhibition of host insects immune response by N.rileyi,which can deepen our understanding of the pathogenic mechanism of entomopathogenic fungus,lays a foundation for the improvement of the virulence of N.rileyi by genetic improvement and other means in the future.In this study,we tested the effect of N.rileyi infection on the innate immune response of the host insect H.armigera,and preliminarily explored the mechanism of its inhibition of innate immunity of H.armigera.The experiment shows as follows:1.Humoral immune response studies have shown that the prophenoloxidase activation reaction of H.armigera was inhibited after infection with N.rileyi.2.The study of cellular immune responses showed that total hemocyte count(THC)of H.armigera was not influenced after infection with N.rileyi,but the ability of hemocytes to phagocytosis,nodulation,and encapsulation responses was significantly reduced,and so was the ability of hemocytes spreading.3.In order to reveal the further mechanism of N.rileyi,in inhibiting the cellular immune response of H.armigera,we use FITC-phalloidin dyeing of H.armigera hemocytes.The results showed that the cytoskeleton of H.armigera hemocytes cytoskeleton was infected after infection with N.rileyi.Disturbance,and then restrained the immune response of each cell.4.An in vitro assay revealed that plasma from N.rileyi infected H.armigera larvae suppressed the spreading ability of hemocytes from naive larvae.This result indicated that the infection of H.armigera could inhibit the immune response of H.armigera by secreting toxic proteins into the hemolymph of the host.5.Furthermore,we isolated the culture filtrate protein of N.rileyi,and also used an in vitro assay,it revealed that the culture filtrate protein of N.rileyi infected H.armigera larvae suppressed the spreading ability of hemocytes from naive larvae.This result indirectly showed that N.rileyi suppressed the immune response of its host,possibly by secreting toxic proteins into the host's hemolymph.The results above preliminarily revealed the mechanism of the innate immune response of N.rileyi in inhibiting host insects:When N.rileyi strains infected H.armigera,it would secrete virulence factors such as toxic proteins or secondary metabolites into the hemolymph of the H.armigera;these virulence factors may be through the destruction of the cytoskeleton of hemocytes,inhibiting the expansion of hemocytes,and then comprehensively repressed hemocyte phagocytosis,nodulation,and encapsulation responses cellular immune responses.In addition,these virulence factors may also inhibit the H.armigera's humoral immune response.N.rileyi inhibited these immune responses,thereby ensuring that it could successfully reproduce in the hemolymph of the H.armigera.6.Finally,in order to identify these virulence factors with immunosuppressive effects,we extracted sera from H.armigera infected with N.rileyi and performed proteomic analysis.Then we detected 31 secreted proteins of the fungi.Later we will further analyze which of these proteins are virulence factors with immunosuppressive effects.In summary,this study initially revealed the mechanism by which N.rileyi impaired innate immunity of its host H.armigera and laid the foundation for further identification of these immunosuppressive virulence factors and functional mechaism in the future.