Abstract
Saccharomyces cerevisiae Yap1 protein is an AP1-like transcription factor involved in the regulation of the oxidative stress response. An ortholog of Yap1, MoAP1, was recently identified from the rice blast fungus Magnaporthe oryzae genome. We found that MoAP1 is highly expressed in conidia and during invasive hyphal growth. The Moap1 mutant was sensitive to H2O2, similar to S. cerevisiae yap1 mutants, and MoAP1 complemented Yap1 function in resistance to H2O2, albeit partially. The Moap1 mutant also exhibited various defects in aerial hyphal growth, mycelial branching, conidia formation, the production of extracellular peroxidases and laccases, and melanin pigmentation. Consequently, the Moap1 mutant was unable to infect the host plant. The MoAP1-eGFP fusion protein is localized inside the nucleus upon exposure to H2O2, suggesting that MoAP1 also functions as a redox sensor. Moreover, through RNA sequence analysis, many MoAP1-regulated genes were identified, including several novel ones that were also involved in pathogenicity. Disruption of respective MGG_01662 (MoAAT) and MGG_02531 (encoding hypothetical protein) genes did not result in any detectable changes in conidial germination and appressorium formation but reduced pathogenicity, whereas the mutant strains of MGG_01230 (MoSSADH) and MGG_15157 (MoACT) showed marketed reductions in aerial hyphal growth, mycelial branching, and loss of conidiation as well as pathogenicity, similar to the Moap1 mutant. Taken together, our studies identify MoAP1 as a positive transcription factor that regulates transcriptions of MGG_01662, MGG_02531, MGG_01230, and MGG_15157 that are important in the growth, development, and pathogenicity of M. oryzae.
Highlights
Organisms such as plants have evolved to develop many efficient defense systems against pathogenic microbes
To examine the molecular mechanisms involved in conidium formation and appressorium development of M. oryzae, we identified the transcriptional factor MoAP1 as a regulator of the oxidative stress response
Our results indicated that MoAP1 is a stage-specific regulator for conidium formation, morphology, aerial hyphal growth, and growth in planta
Summary
Organisms such as plants have evolved to develop many efficient defense systems against pathogenic microbes. During the plant defense response, ROS was used by apoplastic peroxidases on the cell wall to synthesize lignin and other phenolic polymers that prevent pathogen invasion into the host [3]. Plant pathogens have developed many strategies, including enzymatic and non-enzymatic ones, to detoxify ROS and successfully invade their hosts [10,11,12,13]. Transcription factor-mediated hostderived ROS detoxification through regulation of gene expression is important in plant-microbe interactions [14,15,16]. Detoxifying enzymes, either preformed or inducible, including superoxide dismutase, catalases, and peroxidases, are thought to contribute to the tolerance of ROS in pathogenic fungi [15,17,18,19]
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