Redox imaging in the rice blast fungus Magnaporthe oryzae

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 development of infection structures in Magnaporthe oryzae.

To understand redox regulation in oryzae better, we measured the amount and redox potential of glutathione (EGSH), as the major cytoplasmic anti-oxidant, the rates of ROS production, and mitochondrial activity using multi-channel 4-D (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 localised to the growing germ tube and appressorium, but EGSH 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. In contrast there was a dramatic reduction in infection of resistant (IR68) rice, but the sparse hyphae that did form also maintained a similar reducedEGSH.

We conclude that 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.

Samalova, M., Meyer, A. J., Gurr, S. J., & Fricker, M. D. (2014). Robust anti-oxidant defences in the rice blast fungus Magnaporthe oryzae confer tolerance to the host oxidative burst. New Phytol, 201(2), 556-573. doi:10.1111/nph.12530  pdf