Functional Analysis of MoMyb13, a Myb Transcription Factor Involved in Regulating Growth, Conidiation, Hydrophobicity, and Pathogenicity of Magnaporthe oryzae

Abstract

The Myb family of transcription factors (TFs) is a large and functionally diverse group found in all eukaryotes. Its role in fungi remains poorly studied, despite the fact that it is thought to play a role in the pathogenicity of fungal pathogens. In this study, we have characterized the functional role of a Myb family TF called MoMyb13 in the rice blast fungus, Magnaporthe oryzae. MoMyb13 has orthologues only in ascomycete fungi, making it of special interest. Localization experiments confirmed that MoMyb13 is located in the nuclei, as expected for a TF. Phenotypic analysis showed that MoMyb13 mutants exhibited reduced growth, white instead of dark colonies, formed no conidia and, consequently, no conidial appressoria. The mutants completely lost pathogenicity, despite being able to form dark hyphal appressoria at their hyphae ends. Furthermore, the mutant colonies lost hydrophobicity and had significantly reduced expression of the hydrophobin MPG1 that MoMyb13 appears to regulate. However, overexpression of MPG1 in the mutants restored hydrophobicity, but not pathogenicity. Stress assay showed that the mutants were more sensitive to SDS, CR, and H2O2, but more tolerant to NaCl and SOR. In summary, our study revealed the crucial function of MoMyb13 in the growth, conidiation, hydrophobicity, stress response, and pathogenicity of M. oryzae. MoMyb13 is thus needed in the late and very early stages of infection for the spreading of the fungus to other plants and the early establishment of infection in other plants.