title: Stomatal closure by fast abscisic acid signaling is mediated by the guard cell anion channel SLAH3 and the receptor RCAR1.
abstract: S-type anion channels are direct targets of abscisic acid (ABA) signaling and contribute to chloride and nitrate release from guard cells, which in turn initiates stomatal closure. SLAC1 was the first component of the guard cell S-type anion channel identified. However, we found that guard cells of Arabidopsis SLAC1 mutants exhibited nitrate conductance. SLAH3 (SLAC1 homolog 3) was also present in guard cells, and coexpression of SLAH3 with the calcium ion (Ca2+)-dependent kinase CPK21 in Xenopus oocytes mediated nitrate-induced anion currents. Nitrate, calcium, and phosphorylation regulated SLAH3 activity. CPK21-dependent SLAH3 phosphorylation and activation were blocked by ABI1, a PP2C-type protein phosphatase that is inhibited by ABA and inhibits the ABA signaling pathway in guard cells. We reconstituted the ABA-stimulated phosphorylation of the SLAH3 amino-terminal domain by CPK21 in vitro by including the ABA receptor-phosphatase complex RCAR1-ABI1 in the reactions. We propose that ABA perception by the complex consisting of ABA receptors of the RCAR/PYR/PYL family and ABI1 releases CPK21 from inhibition by ABI1, and then CPK21 is further activated by an increase in the cytosolic Ca2+ concentration, leading to its phosphorylation of SLAH3. Thus, the identification of SLAH3 as the nitrate-, calcium-, and ABA-sensitive guard cell anion channel provides insights into the relationship among stomatal response to drought, signaling by nitrate, and nitrate metabolism.
authors.affiliation: Institute for Molecular Plant Physiology and Biophysics, University Würzburg, Julius-von-Sachs Platz 2, D-97082 Würzburg, Germany.
authors.forename: Dietmar
authors.initials: D
authors.lastname: Geiger
authors.forename: Tobias
authors.initials: T
authors.lastname: Maierhofer
authors.forename: Khaled A S
authors.initials: KA
authors.lastname: Al-Rasheid
authors.forename: Sönke
authors.initials: S
authors.lastname: Scherzer
authors.forename: Patrick
authors.initials: P
authors.lastname: Mumm
authors.forename: Anja
authors.initials: A
authors.lastname: Liese
authors.forename: Peter
authors.initials: P
authors.lastname: Ache
authors.forename: Christian
authors.initials: C
authors.lastname: Wellmann
authors.forename: Irene
authors.initials: I
authors.lastname: Marten
authors.forename: Erwin
authors.initials: E
authors.lastname: Grill
authors.forename: Tina
authors.initials: T
authors.lastname: Romeis
authors.forename: Rainer
authors.initials: R
authors.lastname: Hedrich
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D000818:Animals; D000838:Anions; D017360:Arabidopsis / Q000166:cytology / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000502:physiology*; D002352:Carrier Proteins / Q000502:physiology*; D005453:Fluorescence; D047908:Intracellular Signaling Peptides and Proteins; D007473:Ion Channels / Q000502:physiology*; D009566:Nitrates / Q000378:metabolism; D010766:Phosphorylation; D054046:Plant Stomata / Q000502:physiology*; D015398:Signal Transduction; D014982:Xenopus laevis
chemical_list: D000838:Anions; D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007473:Ion Channels; D009566:Nitrates; C540972:RCAR1 protein, Arabidopsis; C582432:SLAH3 protein, Arabidopsis; D000040:Abscisic Acid