title: Chloroplast-generated reactive oxygen species are involved in hypersensitive response-like cell death mediated by a mitogen-activated protein kinase cascade.
abstract: Plant defense against pathogens often includes rapid programmed cell death known as the hypersensitive response (HR). Recent genetic studies have demonstrated the involvement of a specific mitogen-activated protein kinase (MAPK) cascade consisting of three tobacco MAPKs, SIPK, Ntf4 and WIPK, and their common upstream MAPK kinase (MAPKK or MEK), NtMEK2. Potential upstream MAPKK kinases (MAPKKKs or MEKKs) in this cascade include the orthologs of Arabidopsis MEKK1 and tomato MAPKKKalpha. Activation of the SIPK/Ntf4/WIPK pathway induces cell death with phenotypes identical to pathogen-induced HR at macroscopic, microscopic and physiological levels, including loss of membrane potential, electrolyte leakage and rapid dehydration. Loss of membrane potential in NtMEK2(DD) plants is associated with the generation of reactive oxygen species (ROS), which is preceded by disruption of metabolic activities in chloroplasts and mitochondria. We observed rapid shutdown of carbon fixation in chloroplasts after SIPK/Ntf4/WIPK activation, which can lead to the generation of ROS in chloroplasts under illumination. Consistent with a role of chloroplast-generated ROS in MAPK-mediated cell death, plants kept in the dark do not accumulate H(2)O(2) in chloroplasts after MAPK activation, and cell death is significantly delayed. Similar light dependency was observed in HR cell death induced by tobacco mosaic virus, which is known to activate the same MAPK pathway in an N-gene-dependent manner. These results suggest that activation of the SIPK/Ntf4/WIPK cascade by pathogens actively promotes the generation of ROS in chloroplasts, which plays an important role in the signaling for and/or execution of HR cell death in plants.
authors.affiliation: Department of Biochemistry, University of Missouri-Columbia, Columbia, MO 65211, USA.
authors.forename: Yidong
authors.initials: Y
authors.lastname: Liu
authors.forename: Dongtao
authors.initials: D
authors.lastname: Ren
authors.forename: Sharon
authors.initials: S
authors.lastname: Pike
authors.forename: Stephen
authors.initials: S
authors.lastname: Pallardy
authors.forename: Walter
authors.initials: W
authors.lastname: Gassmann
authors.forename: Shuqun
authors.initials: S
authors.lastname: Zhang
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D002245:Carbon Dioxide / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D004573:Electrolytes / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D008027:Light; D048370:MAP Kinase Kinase 2 / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D020935:MAP Kinase Signaling System; D008564:Membrane Potentials; D008928:Mitochondria / Q000502:physiology; D010788:Photosynthesis / Q000502:physiology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D014026:Nicotiana / Q000201:enzymology / Q000378:metabolism* / Q000821:virology; D014027:Tobacco Mosaic Virus / Q000502:physiology
chemical_list: D004573:Electrolytes; D017382:Reactive Oxygen Species; D002245:Carbon Dioxide; D006861:Hydrogen Peroxide; D048370:MAP Kinase Kinase 2