Characterization of a Myb Transcription Factor MoMyb13 Reveals Its Role in Growth, Conidiation, Hydrophobicity and Pathogenicity of Magnaporthe oryzae

The Myb family of transcription factors (TFs) is a large and functionally diverse group found in all eukaryotes, but its role in fungi remains poorly understood. Here, we characterized a Myb family TF called MoMyb13 in the rice blast fungus, Magnaporthe oryzae. MoMyb13 has two Myb domains and has orthologues only in ascomycete fungi. Localization experiments confirmed that MoMyb13 is located in the nuclei, as expected for a TF. Phenotypic analysis showed that MoMyb13 mutants exhibited reduced growth, whitened colony appearance and no conidia formation. Importantly, these mutants completely lost pathogenicity, despite being able to form appressoria at their hyphae ends, suggesting that these appressoria were non-functional for causing infection. Furthermore, the mutant colonies lost hydrophobicity and had significantly reduced expression of the hydrophobin MPG1. However, overexpression of MPG1 in the mutants restored their 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 essential role of the MoMyb13 in the growth, conidiation, hydrophobicity, stress response and pathogenicity of M. oryzae, and provides valuable insights into the working mechanism of Myb TFs in fungi.