title: MAP kinases MPK9 and MPK12 are preferentially expressed in guard cells and positively regulate ROS-mediated ABA signaling.
abstract: Reactive oxygen species (ROS) mediate abscisic acid (ABA) signaling in guard cells. To dissect guard cell ABA-ROS signaling genetically, a cell type-specific functional genomics approach was used to identify 2 MAPK genes, MPK9 and MPK12, which are preferentially and highly expressed in guard cells. To provide genetic evidence for their function, Arabidopsis single and double TILLING mutants that carry deleterious point mutations in these genes were isolated. RNAi-based gene-silencing plant lines, in which both genes are silenced simultaneously, were generated also. Mutants carrying a mutation in only 1 of these genes did not show any altered phenotype, indicating functional redundancy in these genes. ABA-induced stomatal closure was strongly impaired in 2 independent RNAi lines in which both MPK9 and MPK12 transcripts were significantly silenced. Consistent with this result, mpk9-1/12-1 double mutants showed an enhanced transpirational water loss and ABA- and H(2)O(2)-insensitive stomatal response. Furthermore, ABA and calcium failed to activate anion channels in guard cells of mpk9-1/12-1, indicating that these 2 MPKs act upstream of anion channels in guard cell ABA signaling. An MPK12-YFP fusion construct rescued the ABA-insensitive stomatal response phenotype of mpk9-1/12-1, demonstrating that the phenotype was caused by the mutations. The MPK12 protein is localized in the cytosol and the nucleus, and ABA and H(2)O(2) treatments enhance the protein kinase activity of MPK12. Together, these results provide genetic evidence that MPK9 and MPK12 function downstream of ROS to regulate guard cell ABA signaling positively.
authors.affiliation: Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA.
authors.forename: Fabien
authors.initials: F
authors.lastname: Jammes
authors.forename: Charlotte
authors.initials: C
authors.lastname: Song
authors.forename: Dongjin
authors.initials: D
authors.lastname: Shin
authors.forename: Shintaro
authors.initials: S
authors.lastname: Munemasa
authors.forename: Kouji
authors.initials: K
authors.lastname: Takeda
authors.forename: Dan
authors.initials: D
authors.lastname: Gu
authors.forename: Daeshik
authors.initials: D
authors.lastname: Cho
authors.forename: Sangmee
authors.initials: S
authors.lastname: Lee
authors.forename: Roberta
authors.initials: R
authors.lastname: Giordo
authors.forename: Somrudee
authors.initials: S
authors.lastname: Sritubtim
authors.forename: Nathalie
authors.initials: N
authors.lastname: Leonhardt
authors.forename: Brian E
authors.initials: BE
authors.lastname: Ellis
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Murata
authors.forename: June M
authors.initials: JM
authors.lastname: Kwak
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D047468:Immunoprecipitation; D018613:Microscopy, Confocal; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D054046:Plant Stomata / Q000166:cytology / Q000378:metabolism*; D034622:RNA Interference; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*
chemical_list: D029681:Arabidopsis Proteins; D017382:Reactive Oxygen Species; D000040:Abscisic Acid; D020928:Mitogen-Activated Protein Kinases; D002118:Calcium