Characterization Of Parasitic And Immune Factors In The Endoparasitoid Wasp, Microplitis Mediator

Endoparasitoid wasps are important natural enemies of a vast array of agricultural pests. Parasitoid wasps lay their eggs in eggs, larvae, pupae or adults of lepidopteran, coleopteran, and dipteran insects. In egg and larvae stage, parasitoid wasps need to overcome the host defense system, meanwhile they are threatened by a variety of biological agents from the environment and their hosts. Venom, a main resource of parasitic factors, can suppress the host immune responses.Venom apparatus of Microplitis mediator comprises of venom reservoir and two gland filaments, locatted dorsally in the female abdomen. The sections of TEM of venome apparatus showed that the gland filaments mainly consist of a single outer layer composed of secretory cells. The nuclei of secreting cells are relatively large, containing vast amounts of rough endoplasmic reticulum. Therefore, the venom is primarily synthesized in the venom gland, and stored in the reservoir. In vivo, host hemocytes will loss the encapsulated capacity to microbeads after injecting of venom. In vitro study showed that venom could affect cell skeleton, thereby inhibiting normal extension of the cells. The venom proteins affect the host defense system by impairing the encapsulation and extension of host hemocytes.Peptidoglycan recognition proteins(PGRPs) are a family of innate immune receptors that specifically recognize peptidoglycans(PGNs) on the surface of a number of pathogens. Here, we identified and characterized six PGRPs from endoparasitoid wasp, M. mediator(MmePGRPs).To understand the roles of multiple PGRPs in parasitoid wasps, we analyzed their evolutionary relationship and orthology, transcriptional expression duringdifferent developmental stages, and transcriptional expression following infection with Gram-positive and Gram-negative bacteria and with a fungus. MmePGRP-S1 was significantly inducted under all three pathogenic conditions, thus leading us to evaluate gene-specific RNA interference. Double-stranded RNA-mediated knockdown of MmePGRP-S1(MmePGRP-S1 KD) dramatically affected wasp survival following challenge withMicrococcus luteus, indicating the involvement of this particular PGRP in Gram-positive bacterial immunity. This action is likely be mediated by the Toll pathway, but the mechanism remains to be determined. MmePGRP-S1 KD wasps, however, showed differences in survival rate only at 24 h but not 72 h post-infection compared with the controls, indicating a limited role of MmePGRP-S1 against Gram-negative bacteria. MmePGRP-S1 does not play a significant role in anti-fungal immunity as indicated by the survivability of Mme PGRP-S1 KD wasps. This study provides a comprehensive characterization of PGRPs in the economically important hymenopteran species M. mediator.