Gene Cloning and Tissue-Specific Expression of G Protein β Subunit in Microplitis mediator (Hymenoptera: Braconidae)

A gene encoding a novel G protein β subunit of β1 subclass, GβMmed was isolated from Microplitis mediator （Hymenoptera： Braconidae）. The full-length sequence of GβMmed is 1 119 bp, the cDNA contains a 1 023 bp open reading frame that encodes a protein with 340 amino acids, and the predicted molecular weight of GβMmed is 37.23 kDa and isoelectric point is 5.86. By the quantitative real-time RT-PCR method, the tissue-specific expression and quantitative changes in the developmental expression profile of GβMmed were detected. It was found that GβMmed was abundantly expressed in M. mediator antennae, head （without antennae）, thorax, abdomen, legs and the wings, and especially at high levels in abdomen. In antennae, expression varied through 1st day before emergence to 5-d-old adults, and had equal expression levels detected in females and males in total. In head, GβMmed expresses while initially high in females, and have another peaked in stage 4 and 1st day, in males showed a peak of GβMmed expression prior to emergence and relatively low levels after emergence. In female abdomen GβMmed expression levels have two peaks in stage 1 and the 5th d, but just have one peak in male abdomen in stage 1. In all other tissues expression was low and stable.

n-octyl acrylate is a candidate sex pheromone component involved in courtship in parasitoid wasp Microplitis mediator

Sex pheromones are considered to play critical roles in partner communication of most parasitic Hymenoptera.However,the identification of sex pheromone components remains limited to a few families of parasitoid wasps.In this study,we functionally characterized a candidate sex pheromone component in Microplitis mediator(Hymenoptera:Braconidae),a solitary parasitoid of Noctuidae insects.We found that the body surface extract from female wasps could significantly stimulate courtship behavior of males.Gas chromatography-electroantennographic detection(GC-EAD)analysis revealed that a candidate semiochemical from extract triggered significant electrophysiological response of antennae of males.By performing gas chromatography-mass spectrometer(GC-MS)measurement,GC-EAD active compound was identified as n-octyl acrylate,a candidate sex pheromone component in female M.mediator.In electroantennogram(EAG)tests,antennae of male wasps showed significantly higher electrophysiological responses to n-octyl acrylate than those of females.Y-tube olfactometer assays indicated that male wasps significantly chose n-octyl acrylate compared with the control.Furthermore,male wasps showed a remarkable preference for n-octyl acrylate in a simulated field condition behavioral trial;simultaneously,n-octyl acrylate standard could also trigger significant courtship behavior in males.We propose that n-octyl acrylate,as a candidate vital sex pheromone component,could be utilized to design behavioral regulators of M.mediator to implement the protection and utilization of natural enemies.

Molecular characterization and expression of sensory neuron membrane proteins in the parasitoid Microplitis mediator (Hymenoptera: Braconidae)

Sensory neuron membrane proteins(SNMPs),homologs of the human fatty acid transport protein CD36 family,are observed to play a significant role in chemoreception,especially in detecting sex pheromone in Drosophila and some lepidopteran species.In the current study,two full‐length SNMP transcripts,MmedSNMP1 and MmedSNMP2,were identified in the parasitoid Microplitis mediator(Hymenoptera:Braconidae).Quantitative real‐time polymerase chain reaction analysis showed that the expression of MmedSNMP1 was significantly higher in antennae than in other tissues of both sexes.In addition,the MmedSNMP1 transcript was increased dramatically in newly emerged adults and there were no significant differences between adults with or without mating and parasitic experiences.However,compared with MmedSNMP1,the expression of MmedSNMP2 was widely found in various tissues,significantly increased at half‐pigmented pupae stage and remained at a relatively constant level during the following developmental stages.It was found that MmedSNMP1 contained eight exons and seven introns,which was highly conserved compared with other insect species.In situ hybridization assay demonstrated that MmedSNMP1 transcript was distributed widely in antennal flagella.Among selected chemosensory genes(odorant binding protein,odorant receptor,and ionotropic receptor genes),MmedSNMP1 only partially overlapped with MmedORco in olfactory sensory neurons of antennae.Subsequent immunolocalization results further indicated that MmedSNMP1 was mainly expressed in sensilla placodea of antennae and possibly involved in perceiving plant volatiles and sex pheromones.These findings lay a foundation for further investigating the roles of SNMPs in the chemosensation of parasitoids.

Comparative analysis of peptidoglycan recognition proteins in endoparasitoid wasp Microplitis mediator

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 have identified and characterized six PGRPs from endoparasitoid wasp, Microplitis mediator （MmePGRPs）. To understand the roles of PGRPs in parasitoid wasps, we analyzed their evolutionary relationship and orthology, expression profiles during different developmental stages, and transcriptional expression following infection with Gram-positive and -negative bacteria and a fungus. MmePGRP-S1 was significantly induced in response to pathogenic infection. This prompted us to evaluate the effects of RNA interference mediated gene specific knockdown ofMmePGRP-S1. The knockdown of MmePGRP-S1 （iMmePGRP-S1） dramatically affected wasps＇ survival following challenge by Micrococcus luteus, indicating the involvement of this particular PGRP in immune responses against Gram-positive bacteria. This action is likely to be mediated by the Toll pathway, but the mechanism remains to be determined. MmePGRP-S 1 does not play a significant role in anti-fungal immunity as indicated by the survival rate of iMmePGRP-S wasps. This study provides a comprehensive characterization of PGRPs in the economically important hymenopteran species M. mediator.

Characterization and target gene analysis of microRNAs in the antennae of the parasitoid wasp Microplitis mediator

MicroRNAs(miRNAs),a class of non-coding single-strand RNA molecules encoded by endogenous genes,are about 21–24 nucleotides long and are involved in the post-transcriptional regulation of gene expression in plants and animals.Generally,the types and quantities of miRNAs in the different tissues of an organism are diverse,and these divergences may be related to their specific functions.Here we have identified 296 known miRNAs and 46 novel miRNAs in the antennae of the parasitoid wasp Microplitis mediator by high-throughput sequencing.Thirty-three miRNAs were predicted to target olfactory-associated genes,including odorant binding proteins(OBPs),chemosensory proteins,odorant receptors(ORs),ionotropic receptors(IRs)and gustatory receptors.Among these,17 miRNAs were significantly highly expressed in the antennae,four miRNAs were highly expressed both in the antennae and head or wings,while the remaining 12 miRNAs were mainly expressed in the head,thorax,abdomen,legs and wings.Notably,miR-9a-5p and miR-2525-3p were highly expressed in male antennae,whereas miR-1000-5p and novel-miR-13 were enriched in female antennae.The 17 miRNAs highly expressed in antennae are likely to be associated with olfaction,and were predicted to target one OBP(targeted by miR-3751-3p),one IR(targeted by miR-7-5p)and 14 ORs(targeted by 15 miRNAs including miR-6-3p,miR-9a-5p,miR-9b-5p,miR-29-5p,miR-71-5p,miR-275-3p,miR-1000-5p,miR-1000-3p,miR-2525-3p,miR-6012-3p,miR-9719-3p,novel-miR-10,novel-miR-13,novel-miR-14 and novel-miR-28).These candidate olfactory-associated miRNAs are all likely to be involved in chemoreception through the regulation of chemosensory gene expression in the antennae of M.mediator.