title: A Mitogen-activated protein kinase kinase kinase mediates reactive oxygen species homeostasis in Arabidopsis.
abstract: Mitogen-activated protein kinase kinase kinases (MAPKKKs) play key roles in intra- and extracellular signaling in eukaryotes. Here we report that the MAPKKK MEKK1 regulates redox homeostasis in Arabidopsis. We show that MEKK1-deficient plants are misregulated in the expression of a number of genes involved in cellular redox control and accumulate reactive oxygen species (ROS). Most strikingly, homozygous mekk1 mutant plants exhibit a lethal phenotype when developing true leaves. MEKK1 kinase activity and protein stability was regulated by H(2)O(2) in a proteasome-dependent manner and mekk1 plants were compromised in ROS-induced MAPK MPK4 activation. Whereas mpk3 and mpk6 knock out plants showed no defects in development or changes in redox control genes, mpk4 null mutant shared several phenotypic and transcript profile features with mekk1 plants. In agreement with the concept that ROS negatively regulates auxin responses in plants, mekk1 and mpk4 mutants show reduced expression of several auxin-inducible marker genes. Overall, our data defines MPK4 as downstream target of MEKK1 and show that MEKK1 functions in integrating ROS homeostasis with plant development and hormone signaling.
authors.affiliation: Department of Plant Molecular Biology, Max F. Perutz Laboratories, University of Vienna, Dr. Bohrgasse 9, A-1030 Vienna, Austria.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Nakagami
authors.forename: Hanka
authors.initials: H
authors.lastname: Soukupová
authors.forename: Adam
authors.initials: A
authors.lastname: Schikora
authors.forename: Viktor
authors.initials: V
authors.lastname: Zárský
authors.forename: Heribert
authors.initials: H
authors.lastname: Hirt
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000502:physiology*; D001483:Base Sequence; D017931:DNA Primers; D004789:Enzyme Activation; D006706:Homeostasis; D006861:Hydrogen Peroxide / Q000494:pharmacology; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D017931:DNA Primers; D017382:Reactive Oxygen Species; D006861:Hydrogen Peroxide; D020930:MAP Kinase Kinase Kinases