Drosophilaimmunity: theDrosocingene encodes two host defence peptides with pathogen-specific roles

Abstract

Antimicrobial peptides (AMPs) are key to defence against infection in plants and animals. Use of AMP mutations in Drosophila has now revealed that AMPs can additively or synergistically contribute to defence in vivo . However, these studies also revealed high specificity, wherein just one AMP contributes an outsized role in combatting a specific pathogen. Here, we show the Drosocin locus ( CG10816 ) is more complex than previously described. In addition to its namesake peptide ‘Drosocin’, it encodes a second mature peptide from a precursor via furin cleavage. This peptide corresponds to the previously uncharacterized ‘Immune-induced Molecule 7’. A polymorphism (Thr52Ala) in the Drosocin precursor protein previously masked the identification of this peptide, which we name ‘Buletin’. Using mutations differently affecting Drosocin and Buletin, we show that only Drosocin contributes to Drosocin gene-mediated defence against Enterobacter cloacae . Strikingly, we observed that Buletin, but not Drosocin, contributes to the Drosocin gene-mediated defence against Providencia burhodogranariea , including an importance of the Thr52Ala polymorphism for survival. Our study reveals that the Drosocin gene encodes two prominent host defence peptides with different specificity against distinct pathogens. This finding emphasizes the complexity of the Drosophila humoral response and demonstrates how natural polymorphisms can affect host susceptibility.

Ecology-relevant bacteria drive the evolution of host antimicrobial peptides in Drosophila

“…2supp2). However, pricking flies with a needle contaminated with A. sicerae kills ΔAMP14 and Rel E20 flies [17,28], and this systemic infection also causes a severe abdominal bloating phenotype that precedes mortality (shown later). These observations suggest that AMPs regulated by the Imd pathway are required to control A. sicerae .…”

“…The two D. melanogaster Diptericin genes also provide a textbook example of how gene duplication can promote immune novelty, equipping the host with extra copies of immune tools that can be adapted to specific pathogen pressures. Moving forward, it is now clear that AMPs can have strong and specific impacts on survival, and that even single residue polymorphisms can drastically impact infection outcomes [17,21,22]. One goal of infection biology is to try to identify risk factors for susceptibility present in individuals and populations.…”

“…In Drosophila , AMP genes are transcriptionally regulated by the Toll and Imd NF-κB signalling pathways [8]. Recent work has shown individual effector genes can play prominent roles in defence against specific pathogens [12,14,15,17–20]. Consistent with this, population genetics studies have highlighted genetic variants in AMPs correlated with susceptibility against specific pathogens.…”

Lipopolysaccharide -mediated resistance to host antimicrobial peptides and hemocyte-derived reactive-oxygen species are the major Providencia alcalifaciens virulence factors in Drosophila melanogaster

“…A previous in vivo analysis of AMP specificity has shown that Drosocin plays a critical role in controlling Enterobacter cloacae infection [57]. A recent study confirmed this finding [56], however additionally reported that the Drosocin gene encodes not one, but two AMPs: Drosocin and IM7 (newly named as Buletin). Buletin but not Drosocin contributes to host defense against Providencia burhodogranariea infection.…”

“…A similar comparative genomic analysis of clinical Providencia isolates revealed a potential genetic basis underlying diversity in pathogenicity, antibiotic resistance and environmental adaptation of Providencia [54]. Bacteria from the genus Providencia have been widely used to study the mechanisms of Drosophila immunity, particularly the specificity of AMPs [55][56][57][58], individual variability in infection outcome [59], sexual dimorphism in immunity [60], chronic infections [61], host response to infection [62], and intestinal pathologies during aging [63,64]. Strikingly, despite clinical relevance and extensive use in Drosophila immunity research, we know little about Providencia virulence mechanisms.…”