Abstract
Summary Conidiation and appressorium differentiation are key processes for polycyclic dissemination and infection in many pathogens. Our previous study using DNA microarray led to the discovery of the MoYAK 1 gene in M agnaporthe oryzae that is orthologous to YAK 1 in S accharomyces cerevisiae . Although the mechanistic roles of YAK 1 in S . cerevisiae have been described, roles of MoYAK 1 in M . oryzae , a phytopathogenic fungus responsible for rice blast, remain uncharacterized. Targeted disruption of MoYAK 1 results in pleiotropic defects in M . oryzae development and pathogenicity. The Δ M oyak1 mutant exhibits a severe reduction in aerial hyphal formation and conidiation. Conidia in the Δ M oyak1 are delayed in germination and demonstrate decreased glycogen content in a conidial age‐dependent manner. The expression of hydrophobin‐coding genes is dramatically changed in the Δ M oyak1 mutant, leading to a loss of surface hydrophobicity. Unlike the complete inability of the Δ M oyak1 mutant to develop appressoria on an inductive surface, the mutant forms appressoria of abnormal morphology in response to exogenous cyclic adenosine‐5′‐monophosphate and host‐driven signals, which are all defective in penetrating host tissues due to abnormalities in glycogen and lipid metabolism, turgor generation and cell wall integrity. These data indicate that MoYAK 1 is a protein kinase important for the development and pathogenicity of M . oryzae .