Histone H4 is a protein subunit of nucleosomes in eukaryotes and play crucial roles in DNA package and in regulation of gene expression by covalent modification. A viral histone H4 is encoded in a polydnavirus called Cotesia plutellae bracovirus (CpBV). The viral H4 (CpBV-H4) is highly homologous with other H4 proteins except 38 extended residues in N terminus. Its expression alters insect gene expression and suppresses immune and development. In this study, CpBV-H4 was expressed in a natural host, Plutella xylostella, and its suppressive activity on host gene expression was detected by suppressive subtractive hybridization (SSH) technique. SSH targets, of which expressions were down-regulated by CpBV-H4, were read by 454 pyrosequencing and annotated using the published P. xylostella whole genome. Resulting targets were assigned to most GO functional categories. Two chromatin remodeling factors were included in the SSH targets. Lysine demethylase (Px-KDM) of P. xylostella was highly expressed during entire larval period in all tested tissues. However, the suppression of Px-KDM expression by a specific RNA interference (RNAi) did not affect immune response, but significantly impaired the larval development. SWI/SNF of P. xylostella (Px-SWI/SNF) was expressed in all developmental stages. Its RNAi did not affect larval development, but led to significant alteration in adult metamorphosis. CpBV-H4 suppressed expressions of both Px-KDM and Px-SWI/SNF, but its truncated mutant lacking in the extended N-terminal tail did not. These results suggest that the developmental alteration in P. xylostella parasitized by C. plutellae can be caused by an epigenetic control of CpBV-H4 against chromatin remodeling factors.

Cotesia plutellae, an endoparasitoids braconid wasp, possesses a polydnaviruses (PDVs) called Cotesia plutellae bracovirus (CpBV) that encodes viral histone H4 (= CpBV-H4). This viral histone H4 shares high sequence homology (82.5%) with host`s H4 of P.xylostella, except an extended N-terminal tail consisting of 38 amino acid residues with nine lysines. Its extended N-terminal tail has been postulated to play a crucial role in suppressing host immunity, growth and development-associated genes, presumably through an epigenetic control mechanism. A suppression subtractive hybridization (SSH) analysis was analyzed in transcriptome by short-read sequencing technology and provided several target and non-target genes of a viral histone H4. In this study, we analyzed the effect CpBV-H4 on the expression of two target genes: Lysine-specific demethylase (KDM) and Serine proteinase inhibitor (Serpins). Transient expression of CpBV-H4 into non parasitized P. xylostella was performed by microinjection of a recombinant expression vector, and showed the expression up to 70 h. Under this transient expression condition, we analyzed the effect of CpBV-H4 on the expression of target genes by RT-PCR at different time points. Interestingly, the CpBV-H4 significantly inhibited the expression of these target genes, while the truncated CpBV-H4 deleting the N-terminal tail did not show this inhibitory effect. This study also showed that the viral histone H4 suppresses expressions of lysine-specific demethylase and serine proteinase inhibitor (Serpin2) to inhibit host growth and development.

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 viral histone H4 (=CpBV-H4) is encoded in a polydnavirus, Cotesia plutellae bracovirus, and symbiotically associated with an endoparasitoid wasp, C. plutellae. It has an extended N-terminal tail consisting of 38 amino acid residues, compared to the host H4 and this extended N-terminal tail has been postulated to play a crucial role in an epigenetic control of gene expression. The (SSH) suppression subtractive hybridization analysis was analyzed in transcriptome by short-read sequencing technology. The SSH analysis provided several target and nontarget genes of a viral histone H4. In this study, we analyzed the effect CpBV-H4 on the expression of two target genes serpins and histone lysine N-methyl transferase. Transient expression of CpBV-H4 by microinjecting recombinant expression vector to non parasitized larvae of Plutella xylostella showed that it was expressed up to 70 h. Under this transient expression condition, we analyzed the effect of CpBV-H4 on the expression of target genes by RT-PCR at different time points. Interestingly, the CpBV-H4 significantly inhibited the expression of target genes after 44 h, while the truncated CpBV-H4 deleting the N-terminal tail did not show the inhibitory activity.