title: Three SnRK2 protein kinases are the main positive regulators of abscisic acid signaling in response to water stress in Arabidopsis.
abstract: Responses to water stress are thought to be mediated by transcriptional regulation of gene expression via reversible protein phosphorylation events. Previously, we reported that bZIP (basic-domain leucine zipper)-type AREB/ABF (ABA-responsive element-binding protein/factor) transcription factors are involved in ABA signaling under water stress conditions in Arabidopsis. The AREB1 protein is phosphorylated in vitro by ABA-activated SNF1-related protein kinase 2s (SnRK2s) such as SRK2D/SnRK2.2, SRK2E/SnRK2.6 and SRK2I/SnRK2.3 (SRK2D/E/I). Consistent with this, we now show that SRK2D/E/I and AREB1 co-localize and interact in nuclei in planta. Our results show that unlike srk2d, srk2e and srk2i single and double mutants, srk2d srk2e srk2i (srk2d/e/i) triple mutants exhibit greatly reduced tolerance to drought stress and highly enhanced insensitivity to ABA. Under water stress conditions, ABA- and water stress-dependent gene expression, including that of transcription factors, is globally and drastically impaired, and jasmonic acid (JA)-responsive and flowering genes are up-regulated in srk2d/e/i triple mutants, but not in other single and double mutants. The down-regulated genes in srk2d/e/i and areb/abf triple mutants largely overlap in ABA-dependent expression, supporting the view that SRK2D/E/I regulate AREB/ABFs in ABA signaling in response to water stress. Almost all dehydration-responsive LEA (late embryogenesis abundant) protein genes and group-A PP2C (protein phosphatase 2C) genes are strongly down-regulated in the srk2d/e/i triple mutants. Further, our data show that these group-A PP2Cs, such as HAI1 and ABI1, interact with SRK2D. Together, our results indicate that SRK2D/E/I function as main positive regulators, and suggest that ABA signaling is controlled by the dual modulation of SRK2D/E/I and group-A PP2Cs.
authors.affiliation: Biological Resources Division, Japan International Research Center for Agricultural Sciences, Tsukuba, Ibaraki, 305-8686, Japan.
authors.forename: Yasunari
authors.initials: Y
authors.lastname: Fujita
authors.forename: Kazuo
authors.initials: K
authors.lastname: Nakashima
authors.forename: Takuya
authors.initials: T
authors.lastname: Yoshida
authors.forename: Takeshi
authors.initials: T
authors.lastname: Katagiri
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kidokoro
authors.forename: Norihito
authors.initials: N
authors.lastname: Kanamori
authors.forename: Taishi
authors.initials: T
authors.lastname: Umezawa
authors.forename: Miki
authors.initials: M
authors.lastname: Fujita
authors.forename: Kyonoshin
authors.initials: K
authors.lastname: Maruyama
authors.forename: Kanako
authors.initials: K
authors.lastname: Ishiyama
authors.forename: Masatomo
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Shoko
authors.initials: S
authors.lastname: Nakasone
authors.forename: Kohji
authors.initials: K
authors.lastname: Yamada
authors.forename: Takuya
authors.initials: T
authors.lastname: Ito
authors.forename: Kazuo
authors.initials: K
authors.lastname: Shinozaki
authors.forename: Kazuko
authors.initials: K
authors.lastname: Yamaguchi-Shinozaki
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D050976:Basic-Leucine Zipper Transcription Factors / Q000378:metabolism; D003517:Cyclopentanes / Q000378:metabolism; D003681:Dehydration / Q000378:metabolism*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D016254:Mutagenesis, Insertional; D009154:Mutation; D020411:Oligonucleotide Array Sequence Analysis; D054883:Oxylipins / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D000071636:Protein Phosphatase 2C; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D014867:Water / Q000378:metabolism
chemical_list: D000040:Abscisic Acid; D029681:Arabidopsis Proteins; D050976:Basic-Leucine Zipper Transcription Factors; D003517:Cyclopentanes; D054883:Oxylipins; D010749:Phosphoprotein Phosphatases; D000071636:Protein Phosphatase 2C; D017346:Protein Serine-Threonine Kinases; D014867:Water; C508877:At1g45249 protein, Arabidopsis; C492978:SnRK2 protein, Arabidopsis; C011006:jasmonic acid