title: Characterization and expression of a NADP-malic enzyme cDNA induced by salt stress from the facultative crassulacean acid metabolism plant, Mesembryanthemum crystallinum.
abstract: The facultative halophyte and crassulacean acid-metabolism plant, Mesembryanthemum crystallium shifts from C3 photosynthesis to crassulacean acid metabolism when exposed to high-salt or drought conditions. To study the molecular basis of this metabolic transition, the expression of NADP(+)-dependent malic enzyme (NADP-ME), which catalyzes the decarboxylation of malate to release pyruvate and CO2, has been investigated. The complete nucleotide sequence of a full-length cDNA clone was determined and found to contain a single open reading frame encoding a 585-amino-acid polypeptide of 64284 Da. The ice plant (M. crystallinum) NADP-ME shares amino acid identities in the range 72.5-79.0% when compared to other higher-plant enzymes and is more closely related to C3 rather than C4 forms of the enzyme. Genomic Southern-blot analysis of ice-plant DNA indicates that NADP-ME is encoded by a small gene family. Steady-state transcript levels increase 8-10-fold in response to salt stress in the leaves. Transcript levels in roots are extremely low and are unaffected by salt-stress treatment. Nuclear run-on experiments, using isolated nuclei from leaf tissue, confirm that the accumulation of NADP-ME transcripts is, in part, the result of increased transcription of this gene during salt stress.
authors.affiliation: Department of Biochemistry, University of Arizona, Tucson.
authors.forename: J C
authors.initials: JC
authors.lastname: Cushman
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D015139:Blotting, Southern; D002244:Carbon / Q000378:metabolism; D004247:DNA / Q000737:chemistry / Q000235:genetics*; D008291:Malate Dehydrogenase / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D010788:Photosynthesis; D010944:Plants / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D012689:Sequence Homology, Nucleic Acid; D012965:Sodium Chloride / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D012965:Sodium Chloride; D002244:Carbon; D004247:DNA; D008291:Malate Dehydrogenase; C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+)