title: Arabidopsis ABA-Activated Kinase MAPKKK18 is Regulated by Protein Phosphatase 2C ABI1 and the Ubiquitin-Proteasome Pathway.
abstract: Phosphorylation and dephosphorylation events play an important role in the transmission of the ABA signal. Although SnRK2 [sucrose non-fermenting1-related kinase2] protein kinases and group A protein phosphatase type 2C (PP2C)-type phosphatases constitute the core ABA pathway, mitogen-activated protein kinase (MAPK) pathways are also involved in plant response to ABA. However, little is known about the interplay between MAPKs and PP2Cs or SnRK2 in the regulation of ABA pathways. In this study, an effort was made to elucidate the role of MAP kinase kinase kinase18 (MKKK18) in relation to ABA signaling and response. The MKKK18 knockout lines showed more vigorous root growth, decreased abaxial stomatal index and increased stomatal aperture under normal growth conditions, compared with the control wild-type Columbia line. In addition to transcriptional regulation of the MKKK18 promoter by ABA, we demonstrated using in vitro and in vivo kinase assays that the kinase activity of MKKK18 was regulated by ABA. Analysis of the cellular localization of MKKK18 showed that the active kinase was targeted specifically to the nucleus. Notably, we identified abscisic acid insensitive 1 (ABI1) PP2C as a MKKK18-interacting protein, and demonstrated that ABI1 inhibited its activity. Using a cell-free degradation assay, we also established that MKKK18 was unstable and was degraded by the proteasome pathway. The rate of MKKK18 degradation was delayed in the ABI1 knockout line. Overall, we provide evidence that ABI1 regulates the activity and promotes proteasomal degradation of MKKK18.
authors.affiliation: Department of Biotechnology, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University in Poznań, Umultowska 89, 61-614 Poznań, Poland.
authors.forename: Filip
authors.initials: F
authors.lastname: Mitula
authors.affiliation: Department of Biotechnology, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University in Poznań, Umultowska 89, 61-614 Poznań, Poland.
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Tajdel
authors.affiliation: Department of Biotechnology, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University in Poznań, Umultowska 89, 61-614 Poznań, Poland.
authors.forename: Agata
authors.initials: A
authors.lastname: Cieśla
authors.affiliation: Department of Molecular and Cellular Biology, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University in Poznań, Umultowska 89, 61-614 Poznań, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Kasprowicz-Maluśki
authors.affiliation: Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawińskiego 5a, 02-106 Warsaw, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Kulik
authors.affiliation: Institute of Plant Genetics Polish Academy of Science, Strzeszyńska 34, 60-479 Poznań, Poland.
authors.forename: Danuta
authors.initials: D
authors.lastname: Babula-Skowrońska
authors.affiliation: Department of Molecular and Cellular Biology, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University in Poznań, Umultowska 89, 61-614 Poznań, Poland.
authors.forename: Michal
authors.initials: M
authors.lastname: Michalak
authors.affiliation: Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawińskiego 5a, 02-106 Warsaw, Poland.
authors.forename: Grazyna
authors.initials: G
authors.lastname: Dobrowolska
authors.affiliation: Department of Biotechnology, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University in Poznań, Umultowska 89, 61-614 Poznań, Poland.
authors.forename: Jan
authors.initials: J
authors.lastname: Sadowski
authors.affiliation: Department of Biotechnology, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University in Poznań, Umultowska 89, 61-614 Poznań, Poland ludwika@amu.edu.pl.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Ludwików
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D018525:Germination / Q000187:drug effects; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism*; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development; D054046:Plant Stomata / Q000187:drug effects / Q000254:growth & development; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D000071636:Protein Phosphatase 2C; D021381:Protein Transport / Q000187:drug effects; D011523:Protoplasts / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013347:Subcellular Fractions / Q000378:metabolism; D014026:Nicotiana; D014452:Ubiquitins / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D014452:Ubiquitins; D000040:Abscisic Acid; D020930:MAP Kinase Kinase Kinases; C000598433:MAPKKK18 protein, Arabidopsis; C087434:ABI1 protein, Arabidopsis; D010749:Phosphoprotein Phosphatases; D000071636:Protein Phosphatase 2C; D046988:Proteasome Endopeptidase Complex
keywords: ABA signaling; ABI1 PP2C; Arabidopsis thaliana; MAP kinase cascade; MKKK18; Proteasome