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Parasitic wasp Venturia Canescens. © CNRS IRBI, Thomas Steinemann

Parasitic Venturia wasp: a viral accomplice unveiled

A group of French researchers* headed by entomologists from INRA and CNRS, in collaboration with geneticists from CEA, uncovered a new case of a parasitic wasp that has captured the DNA of viruses in its genome, enabling it to circumnavigate the immune defences of host caterpillars. In addition to helping science understand the role viruses play in the evolutionary mechanisms of living organisms, the study also opens up avenues for improving strategies to develop medicine for therapeutic use. The findings were published in Science Advances on 27 November 2015.

Updated on 12/28/2015
Published on 11/30/2015
Keywords: PARASITE - VIRUS - wasp

In the science fiction films “Alien” by Ridley Scott, the protagonists are eaten alive by monstrous creatures whose larvae destroy the human body from within, in a matter of a few days. These monsters were directly inspired by parasitic wasps that are widespread in nature, but that limit their attacks, thankfully, to other insects. Parasitic wasps are an important part of biodiversity and play a key role in controlling insect populations, notably those that feed on crops. A large number of these species lay their eggs and develop in the larval state inside caterpillars that serve as hosts. To do so, they use unique strategies, making use of viruses that allow them to thwart the immune defences of the caterpillars.

A consortium of French researchers* headed by entomologists from INRA and CNRS, in collaboration with geneticists from Genoscope (CEA-Institut de génomique), recently demonstrated that the parasitic wasps have domesticated the same type of virus in its DNA several times over the course of evolution. Each time, the virus is transformed into a “biological weapon” against the host’s immune system. The most recent findings, concerning the Venturia canescens wasp, show that the domesticated virus is used solely for its capacity to form viral envelopes. These envelopes, which are a sort of natural liposome, enable the wasp to wrap immunosuppressive proteins, which the wasp itself synthesises, and introduce them into the immune cells of the host caterpillar to neutralise them.

Viral envelopes (in purple) wrapping immunosuppressive proteins in the ovaries of the Venturia Canescens wasp. © INRA, Marc Ravallec
Viral envelopes (in purple) wrapping immunosuppressive proteins in the ovaries of the Venturia Canescens wasp © INRA, Marc Ravallec
The presence of immunosuppressive particles, which look like small crystals, was described for the first time in the Venturia wasp over 50 years ago. These particles, produced in the wasp’s ovaries, accompany its eggs and protect them against the immune defences of the caterpillar in which they are laid. The nature of these particles, however, has been a mystery until now.

Using a combination of the most recent approaches in decoding genomes and identifying proteins, the researchers shed light on the question by demonstrating that the particles are produced by a virus whose genome is distributed in several fragments into the wasp’s DNA. A virus from the nudivirus group (insect virus close to baculovirus used as a biological tool against caterpillars) was first captured in the Venturia wasp’s genome. Then, only the capacity to form envelopes was retained from the initial virus. Now scientists must study in more detail how the particles are produced and how they get into the host’s cells.

This scenario of domestication of a virus by a eukaryote organism, as extraordinary as it may seem at first, is actually recurrent over the course of the evolution of parasitic wasps. Science has known for several years now that bracovirus, symbiotic viruses associated with another group of more than 17,000 species of parasitic wasps, also comes from a nudivirus captured 100 million years ago by an ancestor of the wasp group. Nevertheless, the strategy used to thwart the immunity of the host is significantly different in the two cases, since Venturia’s particles deliver proteins while bracoviruses are used to transfer genes.

In addition to its interest for the evolutionary sciences, the knowledge acquired on these systems could be of benefit in developing new therapies that ultimately lead to new medicines for man.  Indeed, it may well be that the viral systems of parasitic wasps have become more and more efficient in transporting molecules over millions of years of selection, helping parasitism to thrive.  Such positive developments could lead to great strides in biotechnology.

*Concerned Institutions: INRA, CNRS, CEA-Genoscope, Université de Montpellier, Université François Rabelais de Tours, Université de Nice Sophia Antipolis.

Contact(s)
Scientific contact(s):

  • Anne-Nathalie Volkoff (33 (0)4 67 14 41 18) Joint Research Unit DGIMI Diversity, Genomes and Insects-Microorganisms Interactions
  • Jean-Michel Drezen (33 (0)2 47 36 69 67) Research Institute for Insect Biology Joint Research Unit 7261 CNRS/ Université François Rabelais (Tours)
Press Relations:
INRA News Office (33 (0)1 42 75 91 86)
Associated Division(s):
Plant Health and Environment
Associated Centre(s):
Occitanie-Montpellier

Reference

Apolline Pichon, Annie Bézier, Serge Urbach, Jean-Marc Aury, Véronique Jouan, Marc Ravallec, Julie Guy, François Cousserans, Julien Thézé, Jérémy Gauthier, Edith Demettre, Sandra Schmieder, François Wurmser, Vonick Sibut, Marylène Poirié, Dominique Colinet, Corinne da Silva, Arnaud Couloux, Valérie Barbe, Jean-Michel Drezen, Anne-Nathalie Volkoff. Recurrent DNA virus domestication leading to different parasite virulence strategies. Science Advances, 27 November 2015. DOI: 10.1126/sciadv.1501150