Cloning, characterization and analysis by RNA interference of various genes of the Chelonus inanitus polydnavirus

Abstract

Successful parasitism of some endoparasitic wasps depends on an obligately symbiotic association with polydnaviruses. These unique viruses have a segmented genome consisting of circles of double-stranded (ds) DNA and do not replicate in the parasitized host. They are produced in the wasp's ovary and injected into the host along with the egg. Chelonus inanitus is an egg-larval parasitoid; its polydnavirus (CiV) has been shown to protect the parasitoid larva from the host's immune system and to induce developmental arrest in the prepupal stage. The genome of CiV consists of at least 10-12 segments and five have been sequenced up to now. Here, the complete (CiV12g2) or partial (CiV12g1, CiV16.8g1) cloning of three new CiV genes is reported. All three occur only on one viral segment and have no similarity to other known polydnavirus genes, with the exception of a high similarity of CiV12g1 to CiV14g1 and CiV12g2 to CiV14g2. Furthermore, the first attempt of in vivo application of RNA interference to study the function of polydnavirus genes is shown. Injection of dsRNA of two late-and one early-and late-expressed CiV genes into CiV/venom-containing host eggs partially rescued last-instar larvae from developmental arrest. Injection of the same dsRNAs into parasitized eggs partially reduced parasitoid survival, mainly by preventing the successful emergence of the parasitoid from the host. These viral genes thus seem to be involved in inducing developmental arrest and in keeping the cuticle soft, which appears to be necessary for parasitoid emergence and host feeding.

When parasitic wasps hijacked viruses: genomic and functional evolution of polydnaviruses

“…Like all Cheloninae, C. inanitus oviposits into the eggs of lepidopteran hosts, whereas the other BV-associated wasps inject their eggs inside immune competent larvae (figure 1) [14]. Parasitism strategies involving the oviposition into host eggs versus larvae, exposing the wasp larvae to different physiological contexts, could explain the different panel of virulence proteins found in chelonines [83,84] compared with other wasps.…”

Transcriptional analysis of polydnaviral genes in the course of parasitization reveals segment‐specific patterns

“…Furthermore, the tissue distribution of transcripts of CiV12g1, CiV12g2, CiV14g1, and CiV14g2 has been measured (Bonvin et al, 2004) and RNAi experiments have been carried out with the same genes (Bonvin et al, 2005). The general picture emerging from these observations along with the expression patterns and abundance of the CiV genes is the following.…”

“…Until now, 5 CiV segments have been fully sequenced, namely CiV12, CiV14, CiV14.5, CiV16.8, and CiV21; on these, 8 genes have been identified and their expression has been analysed in the course of parasitization (Johner and Lanzrein, 2002;Wyder et al, 2002;Bonvin et al, 2004Bonvin et al, , 2005. The majority of these genes had been identified on the basis of gene predictions with Fgenesh 1.0 using "Drosophila" and "Human" settings followed by PCR on cDNAs of parasitized hosts of various stages.…”

“…Analysis of relative transcript levels of 8 CiV genes in parasitized and X-ray parasitized hosts revealed 4 patterns of expression, namely early, persistent, intermediate, and late, whereby the highest quantities of transcripts were observed for the late expressed genes in X-ray parasitized larvae (Johner and Lanzrein, 2002;Bonvin et al, 2004). Analysis by RNAi with 3 late expressed CiV genes suggested that they play a role in causing the developmental arrest in the prepupal stage (Bonvin et al, 2005). The CiV genome consists of at least 15 segments with sizes between 9 and 31 kbp.…”

Blurring Borders: Innate Immunity with Adaptive Features

“…This parasitoid wasp is known to take advantage of yet another virus in a similar fashion, a polydnavirus. Polydnaviruses (PDVs) also suppress the immune system of the host and allow the juvenile parasitoids to develop without being encapsulated by host hemocytes [65]. In invertebrates, the ambivalent relation of viruses and their hosts is further complicated by presence of both specific (RNA interference-mediated) and nonspecific (interferon-mediated) antiviral responses supporting the blurring of immunological functions [66].…”