Cross-talk of cellulose and mannan perception pathways leads to inhibition of cellulase production in several filamentous fungi

It is essential for microbes to acquire information about their environment. Fungi use soluble degradation products of plant cell wall components to understand the substrate composition they grow on. Individual signaling pathways have been well described. However, the interconnections between pathways remain poorly understood. In the present work, we provide evidence of “confusion” due to cross-talk between the perception pathways for cellulose and the hemicellulose mannan in several filamentous fungi, leading to the inhibition of cellulase expression. We used the functional genomics tools available for Neurospora crassa to investigate this signaling overlap at the molecular level. Cross-talk and competitive inhibition could be identified both during uptake by cellodextrin transporters and intracellularly. Importantly, the overlap is independent of CRE-1-mediated catabolite repression. These results provide novel insights into the regulatory networks of lignocellulolytic fungi and will contribute to the rational optimization of fungal enzyme production for efficient plant biomass depolymerization and utilization.