Department of Entomology

Abstract: Polydnaviruses (PDVs) occur in obligate symbiotic associations with many endoparasitic ichneumonid (IVs) and braconid (BVs) wasps often valued as biological control agents of lepidopteran agricultural pests. PDVs are injected during parasitization of lepidopteran hosts, and viral gene products disrupt host immunity and development to enable endoparasitoid survival. The Campoletis sonorensis IV (CsIV) vankyrin gene family encodes seven related proteins with ankyrin repeat domains that resemble those of NF-κB transcription factor inhibitors (IkBs) involved in host innate immunity and developmental cascades. CsIV vankyrin gene expression was detected by 2-4 hours post-parasitization (p.p.) and peaked by 3 days p.p. in Heliothis virescens larval hosts. Vankyrin genes were differentially expressed in host immune tissues and divided into two subclasses: those preferentially expressed in the fat body (FB), and those expressed in host blood hemocytes (HC). Polyclonal antibodies raised against FB and HC-specific vankyrins localized to host cell nuclei and detected proteins of the appropriate size in host FB and HC tissue extracts. In transient vankryin expression assays utilizing Drosophila S2 and Sf9 cells, differences in protein localization and stability were observed within and between the subclasses of CsIV vankyrins, and between cells exposed to lipopolysaccharide, laminarin, or viral immune challenge. Suppression of the Spodoptera littoralis immune system with vankyrin co-expression from the baculovirus expression vector system (BEVS) increased the susceptibility of non-permissive S. littoralis larvae to baculovirus infection. Transformed insect Sf9 and Tn5 cells and recombinant baculoviruses expressing two FB-specific vankyrins also exhibited enhanced longevity, enhanced recombinant protein production, and increased recombinant virus propagation post-infection. Together, these data indicated that vankyrin proteins in CsIV have divergent immunosuppressive physiological functions in wasp-parasitized lepidopteran larval hosts. CsIV vankyrins may differentially interact with NF-κB transcription factors disrupting immunity and development at varying stages and in specific tissues of the parasitized H. virescens hosts. This hypothesized activity is consistent with observed variable immunosuppressive physiological effects in the lepidopteran host and in BEVS infected cells. The complexity of vankyrin activities, localization, and expression patterns in insect cells also hints at the inherent intricacy of invertebrate innate immune responses that could be targeted for disruption by genetically engineered crops or baculoviruses carrying these traits.