title: Gamma-aminobutyric acid depletion affects stomata closure and drought tolerance of Arabidopsis thaliana.
abstract: A rapid accumulation of γ-aminobutyric acid (GABA) during biotic and abiotic stresses is well documented. However, the specificity of the response and the primary role of GABA under such stress conditions are hardly understood. To address these questions, we investigated the response of the GABA-depleted gad1/2 mutant to drought stress. GABA is primarily synthesized from the decarboxylation of glutamate by glutamate decarboxylase (GAD) which exists in five copies in the genome of Arabidopsis thaliana. However, only GAD1 and GAD2 are abundantly expressed, and knockout of these two copies dramatically reduced the GABA content. Phenotypic analysis revealed a reduced shoot growth of the gad1/2 mutant. Furthermore, the gad1/2 mutant was wilted earlier than the wild type following a prolonged drought stress treatment. The early-wilting phenotype was due to an increase in stomata aperture and a defect in stomata closure. The increase in stomata aperture contributed to higher stomatal conductance. The drought oversensitive phenotype of the gad1/2 mutant was reversed by functional complementation that increases GABA level in leaves. The functionally complemented gad1/2 x pop2 triple mutant contained more GABA than the wild type. Our findings suggest that GABA accumulation during drought is a stress-specific response and its accumulation induces the regulation of stomatal opening thereby prevents loss of water.
authors.affiliation: Botanical Institute II, Cologne Biocenter, University of Cologne, Zülpicher Str. 47b, 50674 Cologne, Germany. Electronic address: Derejeworku1@yahoo.com.
authors.forename: Dereje Worku
authors.initials: DW
authors.lastname: Mekonnen
authors.affiliation: Botanical Institute II, Cologne Biocenter, University of Cologne, Zülpicher Str. 47b, 50674 Cologne, Germany. Electronic address: ui.fluegge@uni-koeln.de.
authors.forename: Ulf-Ingo
authors.initials: UI
authors.lastname: Flügge
authors.affiliation: Botanical Institute II, Cologne Biocenter, University of Cologne, Zülpicher Str. 47b, 50674 Cologne, Germany; Division of Biochemistry, Department Biology, University Erlangen-Nuremberg, Staudtstr. 5, 91058 Erlangen, Germany. Electronic address: Frank.ludewig@fau.de.
authors.forename: Frank
authors.initials: F
authors.lastname: Ludewig
mesh_terms: D000222:Adaptation, Physiological / Q000528:radiation effects; D000596:Amino Acids / Q000378:metabolism; D017360:Arabidopsis / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D055864:Droughts; D008401:Gas Chromatography-Mass Spectrometry; D005968:Glutamate Decarboxylase / Q000378:metabolism; D008027:Light; D055442:Metabolome / Q000528:radiation effects; D055432:Metabolomics; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D018517:Plant Roots / Q000378:metabolism / Q000528:radiation effects; D018520:Plant Shoots / Q000378:metabolism / Q000528:radiation effects; D054046:Plant Stomata / Q000502:physiology* / Q000528:radiation effects; D014233:Tricarboxylic Acids / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000172:deficiency* / Q000378:metabolism
chemical_list: D000596:Amino Acids; D029681:Arabidopsis Proteins; D014233:Tricarboxylic Acids; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase; C401141:glutamate decarboxylase 2
keywords: GABA; Glutamate decarboxylase; POP2; Stomata closure; Stomatal conductance