The Toll pathway mediates Drosophila resilience to Aspergillus mycotoxins through specific Bomanins

Abstract

Host defense against infections encompasses resistance, which targets microorganisms for neutralization or elimination, and resilience/disease tolerance, which allows the host to withstand/tolerate pathogens and repair damages. In Drosophila, the Toll signaling pathway is thought to mediate resistance against fungal infections by regulating the secretion of antimicrobial peptides, potentially including Bomanins. We found that Aspergillus fumigatus kills Drosophila Toll pathway mutants without invasion because its dissemination is blocked by melanization, suggesting a role for Toll in host defense distinct from resistance. We report that mutants affecting the Toll pathway or the 55C Bomanin locus were susceptible to the injection of two Aspergillus mycotoxins, restrictocin or verruculogen. The vulnerability of 55C deletion mutants to these mycotoxins was rescued by the overexpression of Bomanins specific to each challenge. Mechanistically, flies in which BomS6 was expressed in the nervous system exhibited an enhanced recovery from the tremors induced by injected verruculogen and displayed improved survival. Thus, innate immunity also protects the host against the action of microbial toxins through secreted peptides and thereby increase its resilience to infection.