title: Open stomata 1 (OST1) kinase controls R-type anion channel QUAC1 in Arabidopsis guard cells.
abstract: Under drought stress, the stress hormone ABA addresses the SnR kinase OST1 via its cytosolic receptor and the protein phosphatase ABI1. Upon activation, OST1 phosphorylates the guard cell S-type anion channel SLAC1. Arabidopsis ABI1 and OST1 loss-of-function mutants are characterized by an extreme wilting 'open stomata' phenotype. Given the fact that guard cells express both SLAC- and R-/QUAC-type anion channels, we questioned whether OST1, besides SLAC1, also controls the QUAC1 channel. In other words, are ABI1/OST1 defects preventing both of the guard cell anion channel types from operating properly in terms of stomatal closure? The activation of the R-/QUAC-type anion channel by ABA signaling kinase OST1 and phosphatase ABI1 was analyzed in two experimental systems: Arabidopsis guard cells and the plant cell-free background of Xenopus oocytes. Patch-clamp studies on guard cells show that ABA activates R-/QUAC-type currents of wild-type plants, but to a much lesser extent in those of abi1-1 and ost1-2 mutants. In the oocyte system the co-expression of QUAC1 and OST1 resulted in a pronounced activation of the R-type anion channel. These studies indicate that OST1 is addressing both S-/SLAC- and R-/QUAC-type guard cell anion channels, and explain why the ost1-2 mutant is much more sensitive to drought than single slac1 or quac1 mutants.
authors: Molecular Plant Physiology and Biophysics, Julius-von-Sachs-Institute, University of Würzburg, Julius-von-Sachs Platz 2, D-97082, Würzburg, Germany.
authors: Dennis
authors: D
authors: Imes
authors: Patrick
authors: P
authors: Mumm
authors: Jennifer
authors: J
authors: Böhm
authors: Khaled A S
authors: KA
authors: Al-Rasheid
authors: Irene
authors: I
authors: Marten
authors: Dietmar
authors: D
authors: Geiger
authors: Rainer
authors: R
authors: Hedrich
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D000818:Animals; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D055864:Droughts; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D059828:Plant Cells / Q000187:drug effects / Q000378:metabolism*; D054046:Plant Stomata / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D025941:Protein Interaction Mapping; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D011523:Protoplasts / Q000378:metabolism; D015398:Signal Transduction; D014982:Xenopus laevis / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D008565:Membrane Proteins; C528438:SLAC1 protein, Arabidopsis; D000040:Abscisic Acid; D011494:Protein Kinases; C472139:OST1 protein, Arabidopsis; C087434:ABI1 protein, Arabidopsis; D010749:Phosphoprotein Phosphatases