The Single von Willebrand factor C-domain protein (SVC) coding gene is not involved in the hymenoptaecin upregulation after Israeli acute paralysis virus (IAPV) injection in the bumblebee Bombus terrestris

Abstract

Within insects, inductions of antimicrobial peptides (AMPs) have been reported after different virus challenges. It is believed that this link is not directly induced by the virus itself, but rather indirectly induced by secondary effects of virus infection. Here we explored if direct sensing of the virus could trigger AMP expression. Recently, a cytokine-like molecule vago, a member of the Single von Willebrand factor C-domain (SVC) protein family, has been shown to be induced by virus infection in a Dicer-2 dependent manner. SVCs are also reported to be responsive in relation to multiple environmental challenges including bacterial infections and the nutritional status in the model species Drosophila melanogaster. Within the bumblebee Bombus terrestris only one SVC member has been identified and is proven to be involved in both the host antiviral defense and the basal expression of AMP genes, thereby it is a possible candidate linking virus infection and AMPs induction. Here we showed that the injection of Israeli acute paralysis virus (IAPV) resulted in a higher hymenoptaecin expression at 1dpi. This expression is IAPV specific as neither injection of slow bee paralysis virus (SBPV) nor random dsRNA results in a similar induction at 1dpi. We could not prove that hymenoptaecin expression after IAPV treatment was related to BtSVC, as a silencing experiment did not lower hymenoptaecin induction. This leaves indirect activation by secondary effects of IAPV infection as a mechanism of AMP genes induction, or that IAPV infection influences the AMP expression dynamics which is initially induced by non-virus related triggers.