title: A MAPK pathway mediates ethylene signaling in plants.
abstract: Ethylene signal transduction involves ETR1, a two-component histidine protein kinase receptor. ETR1 functions upstream of the negative regulator CTR1. The similarity of CTR1 to members of the Raf family of mitogen-activated protein kinase kinase kinases (MAPKKKs) suggested that ethylene signaling in plants involves a MAPK pathway, but no direct evidence for this has been provided. Here we show that distinct MAPKs are activated by the ethylene precursor aminocyclopropane-1-carboxylic acid (ACC) in Medicago and Arabidopsis: In Medicago, the ACC-activated MAPKs were SIMK and MMK3, while in Arabidopsis MPK6 and another MAPK were identified. Medicago SIMKK specifically mediated ACC-induced activation of SIMK and MMK3. Transgenic Arabidopsis plants overexpressing SIMKK have constitutive MPK6 activation and ethylene-induced target gene expression. SIMKK overexpressor lines resemble ctr1 mutants in showing a triple response phenotype in the absence of ACC. Whereas MPK6 was not activated by ACC in etr1 mutants, ein2 and ein3 mutants showed normal activation profiles. In contrast, ctr1 mutants showed constitutive activation of MPK6. These data indicate that a MAPK cascade is part of the ethylene signal transduction pathway in plants.
authors.affiliation: Gregor-Mendel-Institute of Molecular Plant Sciences and Institute of Microbiology and Genetics, Vienna Biocenter, University of Vienna, Dr Bohrgasse 9, A-1030 Vienna, Austria.
authors.forename: Fatma
authors.initials: F
authors.lastname: Ouaked
authors.forename: Wilfried
authors.initials: W
authors.lastname: Rozhon
authors.forename: David
authors.initials: D
authors.lastname: Lecourieux
authors.forename: Heribert
authors.initials: H
authors.lastname: Hirt
mesh_terms: D000598:Amino Acids, Cyclic / Q000378:metabolism; D000621:Aminoisobutyric Acids / Q000494:pharmacology; D000625:Aminooxyacetic Acid / Q000494:pharmacology; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005030:Ethylenes / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D020935:MAP Kinase Signaling System / Q000187:drug effects; D029902:Medicago / Q000201:enzymology / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D030821:Plants, Genetically Modified; D015398:Signal Transduction; D013379:Substrate Specificity
chemical_list: D000598:Amino Acids, Cyclic; D000621:Aminoisobutyric Acids; D004791:Enzyme Inhibitors; D005030:Ethylenes; D010940:Plant Proteins; D000625:Aminooxyacetic Acid; C100049:2-aminoisobutyric acid; C023863:1-aminocyclopropane-1-carboxylic acid; D020928:Mitogen-Activated Protein Kinases; C419564:salt stress-induced MAP kinase