title: The regulatory domain of SRK2E/OST1/SnRK2.6 interacts with ABI1 and integrates abscisic acid (ABA) and osmotic stress signals controlling stomatal closure in Arabidopsis.
abstract: ABI1 and ABI2 encode PP2C-type protein phosphatases and are thought to negatively regulate many aspects of abscisic acid (ABA) signaling, including stomatal closure in Arabidopsis. In contrast, SRK2E/OST1/SnRK2.6 encodes an Arabidopsis SnRK2 protein kinase and acts as a positive regulator in the ABA-induced stomatal closure. SRK2E/OST1 is activated by osmotic stress as well as by ABA, but the independence of the two activation processes has not yet been determined. Additionally, interaction between SRK2E/OST1 and PP2C-type phosphatases (ABI1 and ABI2) is not understood. In the present study, we demonstrated that the abi1-1 mutation, but not the abi2-1 mutation, strongly inhibited ABA-dependent SRK2E/OST1 activation. In contrast, osmotic stress activated SRK2E/OST1 even in abi1-1 and aba2-1 plants. The C-terminal regulatory domain of SRK2E/OST1 was required for its activation by both ABA and osmotic stress in Arabidopsis. The C-terminal domain was functionally divided into Domains I and II. Domain II was required only for the ABA-dependent activation of SRK2E/OST1, whereas Domain I was responsible for the ABA-independent activation. Full-length SRK2E/OST1 completely complemented the wilty phenotype of the srk2e mutant, but SRK2E/OST1 lacking Domain II did not. Domain II interacted with the ABI1 protein in a yeast two-hybrid assay. Our results suggested that the direct interaction between SRK2E/OST1 and ABI1 through Domain II plays a critical role in the control of stomatal closure.
authors.affiliation: Laboratory of Plant Molecular Biology, RIKEN Tsukuba Institute, 3-1-1, Koyadai, Tsukuba, Ibaraki 305-0074, Japan.
authors.forename: Riichiro
authors.initials: R
authors.lastname: Yoshida
authors.forename: Taishi
authors.initials: T
authors.lastname: Umezawa
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Mizoguchi
authors.forename: Seiji
authors.initials: S
authors.lastname: Takahashi
authors.forename: Fuminori
authors.initials: F
authors.lastname: Takahashi
authors.forename: Kazuo
authors.initials: K
authors.lastname: Shinozaki
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000378:metabolism / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D050901:Nitrate Reductase; D009995:Osmosis; D010641:Phenotype; D010749:Phosphoprotein Phosphatases / Q000378:metabolism / Q000502:physiology*; D019441:Plant Epidermis / Q000378:metabolism; D010937:Plant Growth Regulators; D030821:Plants, Genetically Modified; D011485:Protein Binding; D011494:Protein Kinases / Q000737:chemistry / Q000502:physiology*; D017434:Protein Structure, Tertiary; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D020798:Two-Hybrid System Techniques
chemical_list: D029681:Arabidopsis Proteins; D010937:Plant Growth Regulators; D049452:Green Fluorescent Proteins; D000040:Abscisic Acid; D050901:Nitrate Reductase; D011494:Protein Kinases; C472139:OST1 protein, Arabidopsis; C087434:ABI1 protein, Arabidopsis; D010749:Phosphoprotein Phosphatases