title: Central functions of bicarbonate in S-type anion channel activation and OST1 protein kinase in CO2 signal transduction in guard cell.
abstract: Plants respond to elevated CO(2) via carbonic anhydrases that mediate stomatal closing, but little is known about the early signalling mechanisms following the initial CO(2) response. It remains unclear whether CO(2), HCO(3)(-) or a combination activates downstream signalling. Here, we demonstrate that bicarbonate functions as a small-molecule activator of SLAC1 anion channels in guard cells. Elevated intracellular [HCO(3)(-)](i) with low [CO(2)] and [H(+)] activated S-type anion currents, whereas low [HCO(3)(-)](i) at high [CO(2)] and [H(+)] did not. Bicarbonate enhanced the intracellular Ca(2+) sensitivity of S-type anion channel activation in wild-type and ht1-2 kinase mutant guard cells. ht1-2 mutant guard cells exhibited enhanced bicarbonate sensitivity of S-type anion channel activation. The OST1 protein kinase has been reported not to affect CO(2) signalling. Unexpectedly, OST1 loss-of-function alleles showed strongly impaired CO(2)-induced stomatal closing and HCO(3)(-) activation of anion channels. Moreover, PYR/RCAR abscisic acid (ABA) receptor mutants slowed but did not abolish CO(2)/HCO(3)(-) signalling, redefining the convergence point of CO(2) and ABA signalling. A new working model of the sequence of CO(2) signalling events in gas exchange regulation is presented.
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California, San Diego, La Jolla, CA, USA.
authors.forename: Shaowu
authors.initials: S
authors.lastname: Xue
authors.forename: Honghong
authors.initials: H
authors.lastname: Hu
authors.forename: Amber
authors.initials: A
authors.lastname: Ries
authors.forename: Ebe
authors.initials: E
authors.lastname: Merilo
authors.forename: Hannes
authors.initials: H
authors.lastname: Kollist
authors.forename: Julian I
authors.initials: JI
authors.lastname: Schroeder
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D000838:Anions / Q000378:metabolism*; D017360:Arabidopsis / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001639:Bicarbonates / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004594:Electrophysiology; D008565:Membrane Proteins / Q000378:metabolism*; D010937:Plant Growth Regulators / Q000494:pharmacology; D011494:Protein Kinases; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D000838:Anions; D029681:Arabidopsis Proteins; D001639:Bicarbonates; D008565:Membrane Proteins; D010937:Plant Growth Regulators; C528438:SLAC1 protein, Arabidopsis; D002245:Carbon Dioxide; D000040:Abscisic Acid; D011494:Protein Kinases; C472139:OST1 protein, Arabidopsis; D002118:Calcium