A nuclear receptor, Met, mediates juvenile hormone (JH) action to control gene expressions associated with metamorphosis in many insects. In this study, we showed that RNA interference (RNAi) of the Met or Kruffel homolog 1 (Kr-h1) induced the precocious metamorphosis of Tribolium castaneum larvae. JH significantly inhibited cellular immune response of T. castaneum hemocyte by suppressing hemocyte-spreading behaviour and nodule formation in response to bacterial injection. However, either RNAi of Met or Kr-h1 expression did not prevent the JH-inhibitory effect on hemocyte behaviors. However, several inhibitors specific to JH membrane action significantly inhibit the JH action hemocytes. These results suggest that JH responsiveness of hemocyte is not mediated by the nuclear receptor.

A viral histone H4 is encoded in a polydnavirus called Cotesia plutellae bracovirus (CpBV), which is symbiotic to an endoparasitoid wasp, C. plutellae. Compared to general histone H4, the viral H4 possesses an extra N-terminal tail containing 38 amino acid residues, which has been presumed to control host gene expression in an epigenetic mode. This study addressed the mutational analysis of extra N-terminal amino acid residues of a viral histone H4 and their epigenetic control efficacy. Mutational analysis was performed by serially deleting each of the nine amino acid residues from N-terminal tail of a viral histone H4. Transient expression of each truncated mutants (K1M-K19) in diamondback moth, Plutella xylostella, was performed by microinjection of a recombinant expression vector and confirmed by RT-PCR. Under transient expression, we analysed the effect of these mutations on target gene, transferin. Interestingly, we found that truncated mutants (K1M-K15) did not inhibit the expression of target gene but mutations thereafter (K6M-K9M) significantly alter its expression. As expected these truncated mutants (K1M-K5M) also inhibit hemocyte nodule formation and development of Plutella xylostella. This suggest that lysine residue (K6) in the N-terminal tail is very crucial for the epigenetic control efficacy of viral histone H4.

A polydnavirus, Cotesia plutellae bracovirus (CpBV), is symbiotic to an endoparasitoid wasp, C. plutellae, which specifically parasitizes young larvae of the diamondback moth, Plutella xylostella. Parasitization by an endoparasitoid wasp, Cotesia plutellae, delays the larval development and metamorphosis in Plutella xylostella. Nutritional deprivation by the wasp may induce these developmental alterations in growing host. This study focussed on the change of insulin signaling of the parasitized host. The parasitized larvae exhibit a significant suppression in insulin-like peptide (ILP) expression, which was induced only by the injection of the CpBV. Reduced ILP expression significantly increased the blood sugar level (trehalose) level in the parasitized host, which was mimicked by starvation. Foxo was expressed in the parasitized larvae, but localized mostly in the nucleus. Overexpression of ILP gene in the parasitized larvae induced translation of Foxo to cytoplasm and significantly decreased trehalose level in the plasma. Interestingly, the overexpression of ILP gene significantly prevented the successful parasitization and allowed the host metamorphosis.

Polydnaviruses (PDVs) are a group of insect viruses and symbiotic to some endoparasitoid wasps classified in to Braconidae and Ichneumonidae. Though a lot of PDV genes are identified and analyzed in the host-parasitoid molecular interactions, PDV replication is still far from our understanding. PDVs are replicated in the wasp ovary during late pupal stage. A PDV, Cotesia plutellae bracovirus (CpBV), is symbiotic to Cotesia plutellae. The C. Plutellae ovary was analyzed in transcriptome by 454 pyrosequencing. The ovarian transcriptome provided several major DNA polymerases including Pol α, Pol δ, and Pol ε. All contigs matched to these polymerases were expressed in C. plutellae. Especially DP1 contig homologous to Pol α was highly expressed during late pupal and female adult stages. Its RNA interference significantly suppressed CpBV viral titre in the ovary. This study suggests a hint that CpBV replication uses a host DNA polymerase, in which Pol α may play a specific role in the viral replication in the ovary.

polydnavirus, Cotesia plutellae bracovirus (CpBV), is symbiotic to an endoparasitoid wasp, C. plutellae, which specifically parasitizes young larvae of the diamondback moth, Plutella xylostella. CpBV contains some genes originated from other insect viruses. CpBV-E94k1 and CpBV-E94k2 are homologous to corresponding baculovirus gene E94k, and may play an important role in host-parasitoid interactions. This study was conducted to confirm the origin and function of CpBV-E94k by analyzing its sequence and functional assays. Our phylogenetic analysis indicates that CpBV acquires these E94k genes from baculoviruses. These two genes were expressed during entire period parasitization period. Expression of these E94ks was also tissue-specific because they were expressed in the hemocyte and fat body, but not in the other tissues. Subsequent analysis of gene function by RNA interference showed that it clearly inhibited host immune and developmental processes

An endoparasitoid wasp, Cotesia plutellae, contains a polydnavirus called C. plutellae bracovirus (CpBV) and induces various physiological alterations of parasitized host along with expressions of viral genes. Two host translation inhibitory factors (HTIFs) encoded in CpBV specifically inhibit host mRNAs at post-transcriptional level. They are expressed in late larval stage of Plutella xylostella parasitized by C. plutellae. To understand their late expression control, promoter region of an HTIF gene called CpBV15α was cloned by inverse PCR. The cloned HTIF upstream region (1,113 bp) possessed a putative JH response element (JHRE) and other promoter elements. The putative promoter region was rejoined with an open reading frame of enhanced green fluorescence protein (EGFP). When the recombinant vector construct was injected into early third instar larvae of nonparasitized P. xylostella, it was expressed in fourth larval instar at 72 h after injection, compared to relatively early expression in 24 h after injection of control construct containing a baculovirus immediate-early promoter. However, recombinant EGFP construct lost the late expression pattern when its promoter region was incomplete by truncating JHRE region. PYR application inhibited EGFP expression of the recombinant construct, but gave little influence on truncated constructs. Interestingly, when the complete promoter construct was injected to pupal stage, its late expression pattern was lost and showed early expression pattern. However, an addition of PYR to pupae, which had been injected with the complete promoter construct, inhibited the reporter gene expression. These results suggest that late expression of a HTIF (CpBV15α) is controlled by its promoter, which is sensitive to host JH titer.

An endoparasitoid wasp, Cotesia plutellae parasitized young larvae of diamondback moth, Plutella xylostella. Parasitized larvae exhibit sign ificant immunosuppression and fail to metamorphose to pupal stage. Especially, during last instar of parasitized P.xylostella, massive nutrients divert from host to wasp development. CpBV15α ,a host translation inhibitory factors encoded in C. Plutella bracovirus(CpBV), plays a crucial role in suppressing host usage of amino acids. Its promoter analysis shows that CpBV15α specifically inhibit host development in late larval period. To understand its inhibitory target, its specific expression was performed in non-parasitized P. xylostella by in vivo transient expression technique. Total plasma proteins were analyzed by 2D gel electrophoresis and determined target genes inhibited by CpBV15α. Immunoprecipation of cellular extract with CpBV15α antibody captured eIF2B. CpBV15α shares sequence homology with eIF5, especially at its eIF2B-binding region. Our results suggest that CpBV15α may sequester eIF2B, which result in malfunctioning of eIF2 cycling to form a translation initiation complex.

An endoparasitoid wasp, Cotesia plutellae parasitized young larval of diamondback moth, Plutella xylostella. Parasitized larva exhibit significant immunosuppression and fail to metamorphose to pupal stage. Especially, during last instar of parasitized P. xylostella, massive nutrients divert from host to wasp development. HTIF (host translation inhibitory factor) encoded in C. Plutella bracovirus (CpBV) play a crucial role in suppressing host usage of amino acids. However, its inhibitory activity is selective by discriminating mRNAs based on their 5’UTR secondary structures. Our RT-PCR and proteomic analysis indicated that arginine kinase mRNA was inhibited by HTIF, but imaginal disc growth factor was not. Arginine kinase and IDGF were persistently expressed in parasitized P. .xylotella with the gradual decrease at the late parasitisation period. Expression of arginine kinase and IDGF were also tissue specific in the gut/epidermis and haemocyte but not in fat bodies. Subsequent analysis of these gene functions by RNA interference explained the benefit of parasitoid for the mRNA discrimination by HTIF.