title: Robust anti-oxidant defences in the rice blast fungus Magnaporthe oryzae confer tolerance to the host oxidative burst.
abstract: Plants respond to pathogen attack via a rapid burst of reactive oxygen species (ROS). However, ROS are also produced by fungal metabolism and are required for the development of infection structures in Magnaporthe oryzae. To obtain a better understanding of redox regulation in M. oryzae, we measured the amount and redox potential of glutathione (E(GSH)), as the major cytoplasmic anti-oxidant, the rates of ROS production, and mitochondrial activity using multi-channel four-dimensional (x,y,z,t) confocal imaging of Grx1-roGFP2 and fluorescent reporters during spore germination, appressorium formation and infection. High levels of mitochondrial activity and ROS were localized to the growing germ tube and appressorium, but E(GSH) was highly reduced and tightly regulated during development. Furthermore, germlings were extremely resistant to external H2O2 exposure ex planta. EGSH remained highly reduced during successful infection of the susceptible rice cultivar CO39. By contrast, there was a dramatic reduction in the infection of resistant (IR68) rice, but the sparse hyphae that did form also maintained a similar reduced E(GSH). We conclude that M. oryzae has a robust anti-oxidant defence system and maintains tight control of EGSH despite substantial oxidative challenge. Furthermore, the magnitude of the host oxidative burst alone does not stress the pathogen sufficiently to prevent infection in this pathosystem.
authors.affiliation: Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK.
authors.forename: Marketa
authors.initials: M
authors.lastname: Samalova
authors.affiliation: INRES, Universität Bonn, Friedrich-Ebert-Allee 144, D-53113, Bonn, Germany.
authors.forename: Andreas J
authors.initials: AJ
authors.lastname: Meyer
authors.affiliation: Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK.|Biosciences, University of Exeter, Devon, EX4 4QD, UK.
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Gurr
authors.affiliation: Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Fricker
mesh_terms: D000975:Antioxidants / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism*; D020082:Magnaporthe / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D008969:Molecular Sequence Data; D012275:Oryza / Q000382:microbiology; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D000975:Antioxidants; D017382:Reactive Oxygen Species; D005978:Glutathione
keywords: Grx1-roGFP2; Magnaporthe oryzae; confocal redox imaging; glutathione; mitochondrial activity; monochlorobimane; reactive oxygen species (ROS); rice blast pathogen response