UC San Diego

Fungal infections are a major source of morbidity and mortality throughout the world, especially in agriculturally relevant plants, humans, and insects. To defend against fungal infections, the fruit fly Drosophila melanogaster employs a robust innate immune system. Infections induce a large number of immune proteins through a number of signaling pathways including the Toll pathway. Some of these proteins have been studied, such as the antimicrobial peptides (AMPs) and Bomanins (Boms); many, however, remain uncharacterized. In Chapter I, I used a candidate approach to identify putative effectors from this set of induced uncharacterized genes. I generated CRISPR/Cas9 mutants and assayed them for survival upon infection with various pathogens. I identified an immunodeficiency in a ΔCG18067 mutant. Additionally, I found a background mutation in the immune induced gene IM14. In Chapter II, I examine the role of IM14 and a related peptide, IM4, in innate immunity. By generating a CRISPR/Cas9 knockout of both genes, Δ(IM4,IM14), I find that the IM4 and IM14 peptides are required for defense against a subset of filamentous fungi, including Fusarium oxysporum, but not other Toll-inducible pathogens, such as Enterococcus faecalis and Candida. glabrata. Further genetic analysis revealed that IM4 and IM14 are each required for defense, although they share some functionality. By generating and assaying a genomic epitope-tagged IM14 construct, I detected in vitro interaction of IM14 peptide in hemolymph with the hyphae of F. oxysporum. These findings identify IM4 and IM14 as a new class of innate immune effectors with humoral activity against a select set of filamentous fungi. Overall, I reveal that several previously uncharacterized genes play a crucial role in the innate immune system of D. melanogaster and could aid in the development of new antifungal treatments.