Characterization of Lignin Peroxidase Genes in the Rice Blast Fungus, Magnaporthe oryzae

Abstract

Magnaporthe oryzae is a causal agent of the rice blast which is one of the most devastating diseases of rice worldwide. The rice blast is considered as an important model for studying plant-fungal pathogen interactions. Plants induce a wide range of defense responses to cope with pathogen attacks. Lignification is one of the induced defense responses and involved in not only fortifying the plant cell wall but also inactivating fungal membranes and secretions. In addition, fungal hyphae may lose plasticity necessary for growth due to the lignification of a hyphal tip. In order to overcome this defense reactions, pathogens secrete lignin-degrading enzymes such as laccases and lignin peroxidases. Two of bZIP transcription factors of the rice blast fungus were found to regulate genes related to pathogenicity, including lignin-degrading enzyme genes. Among these lignin-degrading enzyme genes, the expression levels of MoLIP1 and MoLIP3 were the most notably affected. Therefore, these two genes were chosen for in-depth analysis using gene deletion strategy. There were no significant differences in mycelial growth, conidiation, conidial germination, appressorium formation and resistance of oxidative stress between the wild-type and ΔMolip1 and ΔMolip3 mutants. These results indicated that MoLIP genes were not directly involved in mycelial growth, infection-related morphogenesis and detoxification of reactive oxygen species. However, pathogenicity of the mutants decreased and the invasive growth of the mutants was delayed when the mutants were inoculated on rice leaves and in sheath, respectively. These results suggest that lignin peroxidase is required for early infection stage of M. oryzae.