MAP kinase MKK: A central regulator in the development, toxigenic potential, and pathogenesis of Penicillium expansum infecting pears

Abstract

Penicillium expansum is one of the primary pathogens causing postharvest blue mold of pears, which leads to the spoiling of pulp and produces patulin, endangering food security. Mitogen-activated protein kinase (MAPK) signaling pathway regulates the growth and development, cell wall integrity, and pathogenicity of fungi. Mitogen-activated protein kinase kinase (MKK) in the MAPK signaling pathway has been reflected to be associated with fungal cell wall integrity. Nevertheless, the pivotal function of MKK in the process of P. expansum infection remained unexplored. In this study, MKK was knocked out and repaired by the Agrobacterium-mediated homologous recombination technology to explore the function of MKK in P. expansum infection process. It has been found that the deletion of MKK induces morphological changes in the mutant strain and delayed mycelium and spore growth. Further studies showed that the mutant strain was susceptible to cell wall interference compounds and showed a significant decrease in decay diameters and virulence during the infection of the pears. RT-qPCR analysis showed that the deletion of MKK affected the relative expression levels of its upstream and downstream genes. Our results suggest that MKK is essential in the growth and development, cell wall integrity, pathogenicity, and toxigenic capacity of P. expansum.