Jianqiong Huang

RNAseq analysis of the Drosophila genome has revealed further immune-induced genes. Two genes initially annotated as lncRNAs, CG44404 ( yulü ) and CG45045 ( shenshu ), are strongly induced. We report here that these two genes actually encode highly related secreted peptides found in the Sophophora subgenus of Drosophila species. We have generated single and double null mutants of these loci and found that the double mutant line did not display any enhanced susceptibility to an immune challenge with a panel of bacterial and fungal pathogens, except for Pseudomonas aeruginosa . We did not observe any increased P. aeruginosa burden in yulü-shenshu mutants, suggesting that the two peptides may not be required for resistance to infection. Rather, we find that they provide a level of protection against Outer Membrane Vesicles (OMVs) purified from either P. aeruginosa or Serratia marcescens culture supernatants. We have recently reported that S. marcescens OMVs induce the paralysis of flies through the induction of apoptosis in at least some neurons. Much of the virulence of these OMVs is mediated by the metalloprotease PrtA. While Yulü/Shenshu do not display any protease inhibition activity, the detection of an association between Yulü and the Drosophila complement thioester-containing protein 2 (Tep2) led to the finding that both Tep2 and Tep4 mutants are sensitive to the injection of PrtA while their overexpression significantly protects wild-type flies from the effects of this protease. Both Tep2 and Tep4 are able to inhibit the activity of PrtA in a thioester- and yulü/shenshu -dependent manner. Thus, these Teps may also function as α2-macroglobulins.

Host defense against many Gram-positive bacteria and fungal pathogens is mainly provided by the Toll-dependent systemic immune response in Drosophila . While antimicrobial peptides active against these categories of pathogens contribute only modestly to protection, Bomanin peptides are major effectors of the Toll pathway. Remarkably, flies deleted for the 55C locus that contains 10 Bomanin genes are as sensitive as Toll pathway mutant flies to these infections. Yet, the exact functions of single Bomanins in resistance or resilience to infections remain poorly characterized. Here, we have extensively studied the role of these Bomanin genes. BomT1 functions in resistance to Enterococcus faecalis while playing a role in resilience against Metarhizium robertsii infection, like BomS2. BomT1 and BomT2 prevent the dissemination of Candida albicans throughout the host, even though they are not sufficient to confer protection to immunodeficient flies against this pathogen in survival experiments. Furthermore, BomT1 and BomBc1 mutants are sensitive to an Aspergillus fumigatus ribotoxin. We conclude that 55C Bomanins have defined albeit sometimes overlapping roles in the different facets of host defense against infections.

The Drosophila systemic immune response against many Gram-positive bacteria and fungi is mediated by the Toll pathway. How Toll-regulated effectors actually fulfill this role remains poorly understood as the known Toll-regulated antimicrobial peptide (AMP) genes are active only against filamentous fungi and not against Gram-positive bacteria or yeasts. Besides AMPs, two families of peptides secreted in response to infectious stimuli that activate the Toll pathway have been identified, namely Bomanins and peptides derived from a polyprotein precursor known as Baramicin A (BaraA). Unexpectedly, the deletion of a cluster of 10 Bomanins phenocopies the Toll mutant phenotype of susceptibility to infections. Here, we demonstrate that BaraA is required specifically in the host defense against Enterococcus faecalis and against the entomopathogenic fungus Metarhizium robertsii , albeit the fungal burden is not altered in BaraA mutants. BaraA protects the fly from the action of distinct toxins secreted by these Gram-positive and fungal pathogens, respectively, Enterocin V and Destruxin A. The injection of Destruxin A leads to the rapid paralysis of flies, whether wild type (WT) or mutant. However, a larger fraction of wild-type than BaraA flies recovers from paralysis within 5 to 10 h. BaraAs' function in protecting the host from the deleterious action of Destruxin is required in glial cells, highlighting a resilience role for the Toll pathway in the nervous system against microbial virulence factors. Thus, in complement to the current paradigm, innate immunity can cope effectively with the effects of toxins secreted by pathogens through the secretion of dedicated peptides, independently of xenobiotics detoxification pathways.