title: Salt-dependent expression of ammonium assimilation genes in the halotolerant yeast, Debaryomyces hansenii.
abstract: Debaryomyces hansenii is adapted to grow in saline environments, accumulating high intracellular Na(+) concentrations. Determination of the DhGDH1-encoded NADP-glutamate dehydrogenase enzymatic activity showed that it increased in a saline environment. Thus, it was proposed that, in order to overcome Na(+) inhibition of enzyme activity, this organism possessed salt-dependent mechanisms which resulted in increased activity of enzymes pertaining to the central metabolic pathways. However, the nature of the mechanisms involved in augmented enzyme activity were not analyzed. To address this matter, we studied the expression of DhGDH1 and DhGLN1 encoding glutamine synthetase, which constitute the central metabolic circuit involved in ammonium assimilation. It was found that: (1) expression of DhGDH1 is increased when D. hansenii is grown in the presence of high NaCl concentrations, while that of DhGLN1 is reduced, (2) DhGDH1 expression in Saccharomyces cerevisiae takes place in a GLN3- and HAP2,3-dependent manner and (3) salt-dependent DhGDH1 and DhGLN1 expression involves mechanisms which are limited to D. hansenii and are not present in S. cerevisiae. Thus, salt-dependent regulation of the genes involved in central metabolic pathways could form part of a strategy leading to the ability to grow under hypersaline conditions.
authors.affiliation: Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, 04510, Mexico.
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Guerrero
authors.forename: Cristina
authors.initials: C
authors.lastname: Aranda
authors.forename: Alexander
authors.initials: A
authors.lastname: Deluna
authors.forename: Patrizia
authors.initials: P
authors.lastname: Filetici
authors.forename: Lina
authors.initials: L
authors.lastname: Riego
authors.forename: Víctor Hugo
authors.initials: VH
authors.lastname: Anaya
authors.forename: Alicia
authors.initials: A
authors.lastname: González
mesh_terms: D001483:Base Sequence; D005656:Fungal Proteins / Q000096:biosynthesis* / Q000235:genetics; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects*; D018086:Glutamate Dehydrogenase (NADP+) / Q000096:biosynthesis* / Q000235:genetics; D005974:Glutamate-Ammonia Ligase / Q000096:biosynthesis* / Q000235:genetics; D008969:Molecular Sequence Data; D004718:Saccharomycetales / Q000201:enzymology* / Q000235:genetics; D012965:Sodium Chloride / Q000494:pharmacology*
chemical_list: D005656:Fungal Proteins; D012965:Sodium Chloride; D018086:Glutamate Dehydrogenase (NADP+); D005974:Glutamate-Ammonia Ligase