Multiprotein-bridging factor 1 regulates vegetative growth, osmotic stress, and virulence in Magnaporthe oryzae

Multiprotein bridging factor 1 (MBF1) is a transcriptional co-activator that mediates transcriptional activation by bridging sequence-specific activator like proteins and the TATA-box binding protein (TBP). MBF1 has been well-studied in Arabidopsis thaliana, Saccharomyces cerevisiae, Drosophila melanogaster, and Homo sapiens, but it is not well understood in filamentous fungi. In this study, we report the identification and characterization of a MBF1 ortholog (MoMBF1) in the rice blast fungus Magnaporthe oryzae), which causes the devastating rice blast disease and is an ideal model for studying the growth, development and pathogenic mechanisms of filamentous fungi. MoMBF1 encodes a 161 amino acid protein with a typical MBF1 domain and HTH domain. Bioinformatics were used to analyze the structural domains in MoMBF1 and its phylogenetic relationship to other homologs from different organisms. We have generated MoMBF1 deletion mutants (ΔMoMBF1) and functional complementation transformants, and found that the deletion mutants showed significant defects in vegetative growth and tolerance to exogenous stresses, such as 1 M sorbitol, 0.5 M NaCl, and 5 mM H₂O₂. Moreover, ΔMoMBF1 showed reduced pathogenicity with smaller infection lesions than wild type and the complementation strain, and decreased response to the accumulation of ROS (reactive oxygen species) in planta at the initial infection stage. Taken together, our data indicate that MoMBF1 is required for vegetative growth, pathogenicity and stress response in M. oryzae.