Abstract

Parasitic wasps during oviposition disrupt the host immune reaction and endocrine balance in order to create a suitable environment for the development of their progeny. The wealth of physiological host alterations is mediated by virulence factors encoded by the wasp or, in some cases, by polydnaviruses (PDVs), unique viral symbionts injected into the host at oviposition along with the egg, venom and ovarian secretions. PDVs are among the most powerful immunosuppressors in nature, targeting insect defense barriers at different levels. Analyses of PDV genomes revealed a conserved gene family encoding proteins characterized by ankyrin repeats. These proteins (ANKs) are similar to insect and mammalian IκB, but the lack of regulatory domains for signal-mediated degradation and turnover confers them an immunosuppressive activity.

We used Drosophila as a model to expand the functional analysis of PDV encoded virulence factors, looking at the molecular processes underlying the host endocrine disruption. This approach has disclosed that a member of the immunosuppressive viral ankyrin (ank) gene family of the bracovirus associated with the parasitic wasp Toxoneuron nigriceps also disrupts ecdysone biosynthesis and results in developmental arrest. The multifaceted roles of these virulence factors provide a new framework for a more comprehensive functional analysis of molecular strategies used by many wasps across different evolutionary lineages.