title: Evidence for posttranscriptional activation of gamma-glutamylcysteine synthetase during plant stress responses.
abstract: Glutathione (GSH) is a key component of plant antioxidant defenses. We have sought to determine how the rate-limiting step in GSH biosynthesis, catalyzed by gamma-glutamylcysteine synthase (gammaECS) is regulated in Arabidopsis. Functional complementation of a yeast mutant deficient in this enzyme with an Arabidopsis expression library yielded two cDNAs with sequence identical to the previously described AtgammaECS. Nevertheless, the cellular concentration of GSH in these transformants was only 10% of wild-type concentrations and this was not a result of Cys availability. To explore the possibility that Arabidopsis gammaECS requires additional factors for full catalytic activity, we analyzed the GSH levels and the enzyme activities and transcript levels of both enzymes of the GSH biosynthetic pathway in Arabidopsis suspension cultures subjected to a variety of stresses that raise GSH levels. Our results demonstrate rapid posttranscriptional activation of Arabidopsis gammaECS. The implications of these findings for the mechanisms by which GSH concentrations are regulated during plant-stress responses are discussed.
authors.affiliation: Laboratorium voor Genetica, Department of Genetics, Flanders Interuniversity Institute for Biotechnology, Universiteit Gent, K.L. Ledeganckstraat 35, B-9000, Gent, Belgium.
authors.forename: M J
authors.initials: MJ
authors.lastname: May
authors.forename: T
authors.initials: T
authors.lastname: Vernoux
authors.forename: R
authors.initials: R
authors.lastname: Sánchez-Fernández
authors.forename: M
authors.initials: M
authors.lastname: Van Montagu
authors.forename: D
authors.initials: D
authors.lastname: Inzé
mesh_terms: D000595:Amino Acid Sequence; D000975:Antioxidants / Q000378:metabolism; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D004789:Enzyme Activation; D005816:Genetic Complementation Test; D005721:Glutamate-Cysteine Ligase / Q000235:genetics / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism; D008969:Molecular Sequence Data; D018384:Oxidative Stress; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D000975:Antioxidants; D018076:DNA, Complementary; D018744:DNA, Plant; D005721:Glutamate-Cysteine Ligase; D005978:Glutathione