Arabidopsis Mitogen-Activated Protein Kinase Kinase MKK3 Is Upstream of Group C Mitogen-Activated Protein Kinases and Participates in Pathogen Signaling

• Published in: The Plant cell 2007-10, Vol.19 (10), p.3266-3279
• Main Authors: Dóczi, Róbert, Brader, Günter, Pettkó-Szandtner, Aladár, Rajh, Iva, Djamei, Armin, Pitzschke, Andrea, Teige, Markus, Hirt, Heribert
• Format: Article
• Language: English
• Subjects: Antibodies; Arabidopsis - drug effects; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Enzyme Activation - drug effects; Gene expression regulation; Gene Expression Regulation, Plant - drug effects; Genes; Host-Pathogen Interactions; Hydrogen Peroxide - pharmacology; Immunoblotting; Immunoprecipitation; Lycopersicon esculentum; MAP Kinase Kinase 3 - genetics; MAP Kinase Kinase 3 - metabolism; Mitogen-Activated Protein Kinases - genetics; Mitogen-Activated Protein Kinases - metabolism; Pathogens; Phosphorylation - drug effects; Plant cells; Plant tissues; Plants; Plants, Genetically Modified; Protein Binding - drug effects; Proteins; Protoplasts; Pseudomonas syringae; Pseudomonas syringae - physiology; Reverse Transcriptase Polymerase Chain Reaction; Seedlings; Signal Transduction - drug effects; Tomatoes; Two-Hybrid System Techniques; Yeasts
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.106.050039

Although the Arabidopsis thaliana genome contains genes encoding 20 mitogen-activated protein kinases (MAPKs) and 10 MAPK kinases (MAPKKs), most of them are still functionally uncharacterized. In this work, we analyzed the function of the group B MAPK kinase, MKK3. Transgenic ProMKK3:GUS lines showed basal expression in vascular tissues that was strongly induced by Pseudomonas syringae pv tomato strain DC3000 (Pst DC3000) infection but not by abiotic stresses. The growth of virulent Pst DC3000 was increased in mkk3 knockout plants and decreased in MKK3-overexpressing plants. Moreover, MKK3 overexpression lines showed increased expression of several PR genes. By yeast two-hybrid analysis, coimmunoprecipitation, and protein kinase assays, MKK3 was revealed to be an upstream activator of the group C MAPKs MPK1, MPK2, MPK7, and MPK14. Flagellin-derived flg22 peptide strongly activated MPK6 but resulted in poor activation of MPK7. By contrast, MPK6 and MPK7 were both activated by H₂O₂, but only MPK7 activation was enhanced by MKK3. In agreement with the notion that MKK3 regulates the expression of PR genes, ProPR1:GUS expression was strongly enhanced by coexpression of MKK3-MPK7. Our results reveal that the MKK3 pathway plays a role in pathogen defense and further underscore the importance and complexity of MAPK signaling in plant stress responses.