Using Drosophila as a model system for analyzing insect-fungal interactions

In response to fungal infection, the insect innate immune system produces a group of antimicrobial peptides.  Drosomycin is Drosophila’s prevalent antifungal peptide and homologs are produced by diverse insects.  Its production in response to fungal attack is mainly regulated by the Toll immune pathway.  We used a Drosophila strain with a drosomycin-GFP reporter to examine variation in Drosophila’s immune responses to fungi with different infection strategies, e.g., quick kill via toxins vs. slow kill via invasive growth.  In addition, we used RNA interference (RNAi) to inhibit the function of immune genes in Drosophila and dissect their roles against the different fungi.  Flies lacking the ability to produce dif (dorsal-related immunity factor) showed increased susceptibility to Metarhizium spp.  The virulence of several Metarhizium strains was correlated with resistance to antifungal peptides.  Flies defective in individual recognition proteins for fungal infections did not show altered responses to Metarhizium infection, suggesting that multiple detection mechanisms are required or sufficient to trigger immune pathway activation in response to fungal infection.