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

• Published in: The Journal of biological chemistry Vol. 281; no. 8; pp. 5310 - 5318
• Main Authors: Yoshida, Riichiro, Umezawa, Taishi, Mizoguchi, Tsuyoshi, Takahashi, Seiji, Takahashi, Fuminori, Shinozaki, Kazuo
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 24.02.2006; American Society for Biochemistry and Molecular Biology
• Subjects: Abscisic Acid - pharmacology; Amino Acid Sequence; Arabidopsis; Arabidopsis - metabolism; Arabidopsis - physiology; Arabidopsis Proteins - chemistry; Arabidopsis Proteins - metabolism; Arabidopsis Proteins - physiology; Gene Expression Regulation, Plant; Genes, Plant; Green Fluorescent Proteins - metabolism; Models, Biological; Molecular Sequence Data; Mutation; Nitrate Reductase; Osmosis; Phenotype; Phosphoprotein Phosphatases - metabolism; Phosphoprotein Phosphatases - physiology; Plant Epidermis - metabolism; Plant Growth Regulators; Plants, Genetically Modified; Protein Binding; Protein Kinases - chemistry; Protein Kinases - physiology; Protein Structure, Tertiary; Reverse Transcriptase Polymerase Chain Reaction; Sequence Homology, Amino Acid; Signal Transduction; Two-Hybrid System Techniques
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M509820200

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.