title: AIK1, A Mitogen-Activated Protein Kinase, Modulates Abscisic Acid Responses through the MKK5-MPK6 Kinase Cascade.
abstract: The mitogen-activated protein kinase (MAPK) cascade is an evolutionarily conserved signal transduction module involved in transducing extracellular signals to the nucleus for appropriate cellular adjustment. This cascade essentially consists of three components: a MAPK kinase kinase (MAPKKK), a MAPK kinase, and a MAPK, connected to each other by the event of phosphorylation. Here, we report the characterization of a MAPKKK, ABA-INSENSITIVE PROTEIN KINASE1 (AIK1), which regulates abscisic acid (ABA) responses in Arabidopsis (Arabidopsis thaliana). T-DNA insertion mutants of AIK1 showed insensitivity to ABA in terms of both root growth and stomatal response. AIK1 functions in ABA responses via regulation of root cell division and elongation, as well as stomatal responses. The activity of AIK1 is induced by ABA in Arabidopsis and tobacco (Nicotiana benthamiana), and the Arabidopsis protein phosphatase type 2C, ABI1, a negative regulator of ABA signaling, restricts AIK1 activity by dephosphorylation. Bimolecular fluorescence complementation analysis showed that MPK3, MPK6, and AIK1 interact with MKK5. The single mutant seedlings of mpk6 and mkk5 have similar phenotypes to aik1, but mkk4 does not. AIK1 was localized in the cytoplasm and shown to activate MKK5 by protein phosphorylation, which was an ABA-activated process. Constitutively active MKK5 in aik1 mutant seedlings complements the ABA-insensitive root growth phenotype of aik1 The activity of MPK6 was increased by ABA in wild-type seedlings, but its activation by ABA was impaired in aik1 and aik1 mkk5 mutants. These findings clearly suggest that the AIK1-MKK5-MPK6 cascade functions in the ABA regulation of primary root growth and stomatal response.
authors.affiliation: Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China (K.L., F.Y., G.Z., S.S., Y.M., C.-P.S.); and.|State Key Laboratory of Plant Physiology and Biochemistry, China Agricultural University, Beijing 100193, China (Y.L., D.R.).
authors.forename: Kun
authors.initials: K
authors.lastname: Li
authors.affiliation: Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China (K.L., F.Y., G.Z., S.S., Y.M., C.-P.S.); and.|State Key Laboratory of Plant Physiology and Biochemistry, China Agricultural University, Beijing 100193, China (Y.L., D.R.).
authors.forename: Fengbo
authors.initials: F
authors.lastname: Yang
authors.affiliation: Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China (K.L., F.Y., G.Z., S.S., Y.M., C.-P.S.); and.|State Key Laboratory of Plant Physiology and Biochemistry, China Agricultural University, Beijing 100193, China (Y.L., D.R.).
authors.forename: Guozeng
authors.initials: G
authors.lastname: Zhang
authors.affiliation: Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China (K.L., F.Y., G.Z., S.S., Y.M., C.-P.S.); and.|State Key Laboratory of Plant Physiology and Biochemistry, China Agricultural University, Beijing 100193, China (Y.L., D.R.).
authors.forename: Shufei
authors.initials: S
authors.lastname: Song
authors.affiliation: Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China (K.L., F.Y., G.Z., S.S., Y.M., C.-P.S.); and.|State Key Laboratory of Plant Physiology and Biochemistry, China Agricultural University, Beijing 100193, China (Y.L., D.R.).
authors.forename: Yuan
authors.initials: Y
authors.lastname: Li
authors.affiliation: Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China (K.L., F.Y., G.Z., S.S., Y.M., C.-P.S.); and.|State Key Laboratory of Plant Physiology and Biochemistry, China Agricultural University, Beijing 100193, China (Y.L., D.R.).
authors.forename: Dongtao
authors.initials: D
authors.lastname: Ren
authors.affiliation: Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China (K.L., F.Y., G.Z., S.S., Y.M., C.-P.S.); and miaoych@henu.edu.cn songcp@henu.edu.cn.|State Key Laboratory of Plant Physiology and Biochemistry, China Agricultural University, Beijing 100193, China (Y.L., D.R.) miaoych@henu.edu.cn songcp@henu.edu.cn.
authors.forename: Yuchen
authors.initials: Y
authors.lastname: Miao
authors.affiliation: Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, Department of Biology, Henan University, Kaifeng 475001, China (K.L., F.Y., G.Z., S.S., Y.M., C.-P.S.); and miaoych@henu.edu.cn songcp@henu.edu.cn.|State Key Laboratory of Plant Physiology and Biochemistry, China Agricultural University, Beijing 100193, China (Y.L., D.R.) miaoych@henu.edu.cn songcp@henu.edu.cn.
authors.forename: Chun-Peng
authors.identifier: 0000-0001-8774-4309
authors.initials: CP
authors.lastname: Song
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism* / Q000494:pharmacology; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D054046:Plant Stomata / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D014026:Nicotiana / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D000040:Abscisic Acid; C436293:MPK6 protein, Arabidopsis; D020928:Mitogen-Activated Protein Kinases; C519872:MKK5 protein, Arabidopsis; C571388:MKKK20 protein, Arabidopsis; D020929:Mitogen-Activated Protein Kinase Kinases; C087434:ABI1 protein, Arabidopsis; D010749:Phosphoprotein Phosphatases