Bacteria-induced defense responses in the filamentous fungus Coprinopsis cinerea

In the past few years, our laboratory has taken a reductionistic confrontation approach to study molecular defense strategies of the filamentous coprophilic fungus Coprinopsis cinerea (Cc) against Gram-positive and Gram-negative (G+ and G-) bacterial competitors. Thereby, antibacterial mechanisms of Cc were identified, comprising the novel peptide-based antibiotic copsin [1] as well as putative fungal enzymes hydrolyzing bacterial quorum sensing molecules of the homoserine lactone class [2]. Besides these constitutive defense lines of Cc, RNAseq data revealed the upregulation of (antibacterial) genes within its vegetative mycelium onto challenge with G+ and G- bacteria respectively. Since the two sets of upregulated fungal genes overlap to a high degree (Kombrink; manuscript in preparation), the presence of a common elicitor of Cc defense gene induction can be hypothesized. Furthermore, confrontation assays with axenic bacterial Cell Free Supernatants (CFSs) showed similar fungal induction potentials as bacterial cell culture challenges, pointing towards a secreted compound. (Stöckli; unpublished). To confirm this hypothesis of bacteria-induced defense responses in Cc via secreted bacterial elicitor(s), fungal strains were constructed in which promoters of upregulated antibacterial genes are fused to the dTomato reporter gene. Hereby, the inductive potential of bacterial CFS fractions and peptidoglycan preparations can be tracked via immunoblotting or microfluidic and fluorescence-microscopic devices. Once the bacterial elicitor/s is identified and structurally characterized, the nature of the fungal receptor/s sensing the elicitor/s could be revealed by using Cc defense gene knockout strains. Overall, the successful identification of bacterial elicitor/s and fungal receptor/s could enable comparative studies on how conserved this inter-kingdom communication is between bacteria and other fungi of the same or different ecotypes as Cc.

[1] Essig et al., 2014; The Journal of Biological Chemistry, 289(50).

[2] Stöckli et al., 2016; Fungal Genetics and Biology, 102.