title: A novel gamma-hydroxybutyrate dehydrogenase: identification and expression of an Arabidopsis cDNA and potential role under oxygen deficiency.
abstract: In plants, gamma-aminobutyrate (GABA), a non-protein amino acid, accumulates rapidly in response to a variety of abiotic stresses such as oxygen deficiency. Under normoxia, GABA is catabolized to succinic semialdehyde and then to succinate with the latter reaction being catalyzed by succinic semialdehyde dehydrogenase (SSADH). Complementation of an SSADH-deficient yeast mutant with an Arabidopsis cDNA library enabled the identification of a novel cDNA (designated as AtGH-BDH for Arabidopsis thaliana gamma-hydroxybutyrate dehydrogenase), which encodes a 289-amino acid polypeptide containing an NADP-binding domain. Constitutive expression of AtGHBDH in the mutant yeast enabled growth on 20 mm GABA and significantly enhanced the cellular concentrations of gamma-hydroxybutyrate, the product of the GHDBH reaction. These data confirm that the cDNA encodes a polypeptide with GHBDH activity. Arabidopsis plants subjected to flooding-induced oxygen deficiency for up to 4 h possessed elevated concentrations of gamma-hydroxybutyrate as well as GABA and alanine. RNA expression analysis revealed that GHBDH transcription was not up-regulated by oxygen deficiency. These findings suggest that GHBDH activity is regulated by the supply of succinic semialdehyde or by redox balance. It is proposed that GHBDH and SSADH activities in plants are regulated in a complementary fashion and that GHBDH and gamma-hydroxybutyrate function in oxidative stress tolerance.
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
authors.forename: Kevin E
authors.initials: KE
authors.lastname: Breitkreuz
authors.forename: Wendy L
authors.initials: WL
authors.lastname: Allan
authors.forename: Owen R
authors.initials: OR
authors.lastname: Van Cauwenberghe
authors.forename: Cornelis
authors.initials: C
authors.lastname: Jakobs
authors.forename: Driss
authors.initials: D
authors.lastname: Talibi
authors.forename: Bruno
authors.initials: B
authors.lastname: Andre
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Shelp
mesh_terms: D000409:Alanine / Q000737:chemistry; D000445:Aldehyde Oxidoreductases / Q000378:metabolism; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology*; D018076:DNA, Complementary / Q000378:metabolism; D005816:Genetic Complementation Test; D006884:Hydroxybutyrate Dehydrogenase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism; D010455:Peptides / Q000737:chemistry; D010940:Plant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D050644:Succinate-Semialdehyde Dehydrogenase; D013997:Time Factors; D015854:Up-Regulation; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D010455:Peptides; D010940:Plant Proteins; D005680:gamma-Aminobutyric Acid; D006884:Hydroxybutyrate Dehydrogenase; C019416:4-hydroxybutyrate dehydrogenase; D000445:Aldehyde Oxidoreductases; D050644:Succinate-Semialdehyde Dehydrogenase; D000409:Alanine; D010100:Oxygen