Polydnavirus

The Polydnaviren are a family of enveloped viruses with double-stranded, segmented DNA genome, which are integrated into the genome of some parasitic wasps and serve as a viral vector for influencing the hosts of the parasitic wasp larvae. The family contains two genera each other with low homology, the Ichnoviren with simple lipid bilayer and the Bracoviren double lipid bilayer in their respective viral envelope. The former occur in Ichneumonidae, while the latter occur in Braconidae.

Properties

While Ichnoviren transmission electron microscopy an ovoid shape possess ( Ascoviridae - like morphology ), Bracoviren are rod-shaped ( Baculoviridae -like). The emergence of Polydnaviren is dated to about 70 million years before our era, and is now carried over to the offspring (vertical infection). Polydnaviren are descended from the Nudiviren.

Polydnaviren are part of a unique host -pathogen relationship between parasitoid ichneumon, the parasitized caterpillars (mostly Lepidoptera ) and the symbiotic virus of the parasitic wasp. The viral genome is integrated into the genome of the parasitic wasp, while the virions are formed only in the Calyxzellen the ovaries and are injected along with the wasp eggs in the parasitized caterpillar. The virus modulates protect the immune system, metabolism and behavior of the parasitized caterpillar without being replicated therein. Polydnaviren and parasitic wasps thus have a symbiotic mutualism, because the virus used as a vector for transient gene transfer, while the wasps only care in their ovaries for its propagation.

Inhibition of defense responses

The modulation of the immune response to the injected eggs in the parasitized hosts prevents usually occurring immune response. This consists of an encapsulation of the eggs with the hemocytes of Mixocoels that then by further hemocytes of the phenoloxidase melanin oxygen supply reduces the foreign body, thereby slowing down the development of a pathogen or terminated. Polydnaviren can also inactivate including through inhibition of NF -kB in these hemocytes or destroy what this defense weakens. The Cotesia rubecula Polydnavirus of encoding the protein CrV1 which actin filaments depolymerized in hemocytes, thus their mobility and stability is limited. The Bracovirus of Microplitis demolitor ( MDBV ) induces apoptosis in hemocytes by PTP -H2, which occurs less defensive and more liquid food is available. Furthermore, phagocytosis and adhesion of hemocytes is mitigated by the gene GLC1.8, which further reduces the defense. By Egf1.0 the phenol oxidase is inhibited, which prevents the formation of melanin in the course of the immune response. The protein Ankyris inhibits the action of antiviral peptides. In some Ichnoviren Vankyrin inhibits the induction of apoptosis. In addition Polydnaviren induce in the host hyperglycemia, improving the food supply for the ichneumon larvae.

Furthermore Polydnaviren lead to behavioral changes in parasitized caterpillars, which failed after an infection hiking, and pupation to protect the hatched from her and verpuppenden ichneumon larvae from predators or other parasitoids, until the own energy reserves are depleted and the caterpillar dies. Polydnaviren are the first known case of a gene transfer vector, which is used by parasitoids in addition to the modulation of the immune system and metabolism to behavioral changes in the host. Furthermore, it is the first known case that protect hosts to self-abandonment, the descendants of their parasites or parasitoids outside of her body.

Virus - like particles

Some Polydnaviren only produce virus - like particles (VLP ) contained no nucleic acids that have to dampen the immune response, eg Venturia canescens ( Ichneumonidea ) and Leptopilina sp. ( Figitidaea ). The VLP of V. canescens ( VcVLP1, VcVLP2, VcNEP ... ) are produced in Calyxzellen to be released into the fallopian tube. Since the DNA sequences of the VLP proteins having greater similarity to proteins Hymenoptera than viral proteins, a non-viral origin has been suggested.

The wasp Leptopilina heterotoma secreted VLP, which can penetrate the lamellocytes.