The CfMK1 Gene Regulates Reproduction, Appressorium Formation, and Pathogenesis in a Pear Anthracnose-Causing Fungus

Colletotrichum fructicola, the causal agent of pear anthracnose, causes significant annual economic losses. Mitogen-activated protein kinase (MAPK) cascades are highly conserved signal transduction pathways that play a crucial role in mediating cellular responses to environmental and host signals in plant pathogenic fungi. In this study, we identified an ortholog of the FUS3/KSS1-related MAPK gene, CfMK1, and characterized its function in C. fructicola. The Cfmk1 deletion mutants exhibited poorly developed aerial hyphae, autolysis, no conidial mass or perithecia on solid plates. However, the conidiation of the Cfmk1 mutant in PDB liquid medium was normal compared with that of the wild type (WT). Conidia of the Cfmk1 mutant exhibited a reduced germination rate on glass slides or plant surfaces. The Cfmk1 deletion mutants were unable to form appressoria and lost the capacity to penetrate plant epidermal cells. The ability of the Cfmk1 mutants to infect pear leaves and fruit was severely reduced. Moreover, RNA sequencing (RNA-seq) analysis of the WT and Cfmk1 mutant was performed, and the results revealed 1886 upregulated and 1554 downregulated differentially expressed genes (DEGs) in the mutant. The DEGs were significantly enriched in cell wall and pathogenesis terms, which was consistent with the defects of the Cfmk1 mutant in cell wall integrity and plant infection. Overall, our data demonstrate that CfMK1 plays critical roles in the regulation of aerial hyphal growth, asexual and sexual reproduction, autolysis, appressorium formation, and pathogenicity.