Analysis of Serine Proteases involved in Drosophila melanogaster immunity and identification of potential biocontrol agents

Abstract

Although the fruit fly Drosophila melanogaster is not an agricultural pest and does not transmit pathogens to humans, it has been used as a model to decipher innate immune responses and to study host-pathogens interactions. Antimicrobial peptides are a major component of insects’ immunity and their production is mainly controlled by two pathways: Toll and IMD. In response to fungal or Gram-positive bacterial infections, the Toll signaling pathway is activated by a cascade of Serine Proteases (SPs) leading to the cleavage of the cytokine Spz, the Toll ligand. Several SPs have been shown to act upstream of Toll, linking microbial recognition to the cleavage of Spz. Other SPs have also been shown to mediate the flies’ melanization reaction. Serine Protease inhibitors or serpins (SPN) are negative regulators of melanization and AMPs production. Large numbers of SPs and several serpins remain unexplored and the complexity of proteolytic cascades operating upstream of Toll during the flies’ immune response is not completely understood. Using an in vivo RNAi approach, we screened the unexplored SPs for their potential role in Toll activation. We also collected different naturally occurring fungi from dead arthropods and tested their pathogenicity on lab insect models in the aim of a potential utilization as new biological pest control agents.