The Mitogen-Activated Protein Kinase Governs Appressorium Formation, Melanin Synthesis, and Plant Infection of .

The fungus infects plant hosts with a specialized cell called an appressorium, which is melanized and required for plant cell wall penetration. Here, we show that the mitogen-activated protein kinase governs appressorium formation and virulence in the poplar anthracnose fungus . Deletion of impairs aerial hyphal growth and biomass accumulation, and is responsible for the expression of melanin biosynthesis-associated genes. deletion mutants are unable to form appressorium and lose the capacity to colonize either wounded or unwounded poplar leaves, leading to loss of virulence. We demonstrate that the exogenous application of cAMP fails to restore defective appressorium formation in the deletion mutants, suggesting that may function downstream or independent of a cAMP-dependent signal for appressorium formation. Moreover, mutants were sensitive to high osmosis, indicating that plays an important role in stress response. We conclude that plays a vital role in regulating appressorium formation, melanin biosynthesis, and virulence in .