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WRKYs phosphorylated by MAPK regulate chloroplast-mediated ROS burst in plant immunity

Hirofumi Yoshioka: Nagoya University

<div>Plants have evolved two types of immune systems; pattern-triggered immunity (PTI) and effector-triggered immunity (ETI) often accompanied by HR cell death. WRKY transcription factors function in plant immunity through phosphorylation by MAPKs. However, downstream signaling of the WRKYs is largely unknown. We investigated genes regulated by MAPK-WRKY phosphorylation pathway by RNA-seq. We found that plant immune WRKYs downregulate the large number of photosynthesis-related genes and inhibit photosynthetic CO<sub>2</sub> fixation, resulting in generation of reactive oxygen species (ROS) in chloroplasts responsible for cell death. The MAPK-WRKY network controls the chloroplastic ROS burst to establish robust ETI to a plant pathogen. Furthermore, gain- and loss-of-function analyses indicated that six WRKYs are redundantly involved in ETI-triggered chloroplastic ROS burst in <em>Nicotiana</em> <em>benthamiana</em>. We have reported that the MAPK-WRKY cascades in ETI are involved in transcriptional activation of the gene for plasma membrane plant NADPH oxidase in<em> N. benthamiana</em>. We propose that plants developed two ROS-generating systems via immune MAPK-WRKY network in light-dependent and independent manners.</div>