Mitogen-activated protein kinase (MAPK) cascades are highly conserved signal transduction pathways that mediate cellular responses to various biotic and abiotic signals in plant pathogenic fungi. Here, we identified the orthologs of two MAPK genes (CcHog1 and CcSlt2) and assessed their functions by gene deletion and transcriptional analysis methods in Cytospora chrysosperma, the causal agent of canker disease in a wide range of woody plants. We found that the MAPKs shared convergent and distinct roles in fungal development, stress responses and virulence. For example, CcHog1, CcSlt2 and CcPmk1 were all involved in conidiation and response to stresses, including hyperosmotic pressure, cell wall inhibition agents and H2O2, but only CcPmk1 and CcSlt2 were required for hyphal growth and fungal pathogenicity. RNA-Seq data showed that numerous hyperosmosis and cell wall related genes significantly reduced their expression levels in ΔCcHog1 and ΔCcSlt2, respectively. Importantly, RNA and ribosome related processes were significantly enriched in the up-regulated genes of ΔCcSlt2, while they were significantly enriched in the down-regulated genes of ΔCcPmk1. Moreover, some secondary metabolite biosynthesis core genes (20/68) and two gene clusters were regulated by at least one among CcPmk1, CcHog1 and CcSlt2. Importantly, some virulence-associated genes were significantly down-regulated in ΔCcPmk1 and/or ΔCcSlt2, such as candidate effector genes. Collectively, these results suggest that the similar and distinct phenotypes of each MAPKs mutant may result from the transcriptional regulation of a series common or specific downstream genes, which provide a better understanding of the regulation network of MAPKs in C. chrysosperma.
Keywords: Fungal Pathogens; Host Parasite Interactions.