title: Analysis of cytosolic and plastidic serine acetyltransferase mutants and subcellular metabolite distributions suggests interplay of the cellular compartments for cysteine biosynthesis in Arabidopsis.
abstract: In plants, the enzymes for cysteine synthesis serine acetyltransferase (SAT) and O-acetylserine-(thiol)-lyase (OASTL) are present in the cytosol, plastids and mitochondria. However, it is still not clearly resolved to what extent the different compartments are involved in cysteine biosynthesis and how compartmentation influences the regulation of this biosynthetic pathway. To address these questions, we analysed Arabidopsis thaliana T-DNA insertion mutants for cytosolic and plastidic SAT isoforms. In addition, the subcellular distribution of enzyme activities and metabolite concentrations implicated in cysteine and glutathione biosynthesis were revealed by non-aqueous fractionation (NAF). We demonstrate that cytosolic SERAT1.1 and plastidic SERAT2.1 do not contribute to cysteine biosynthesis to a major extent, but may function to overcome transport limitations of O-acetylserine (OAS) from mitochondria. Substantiated by predominantly cytosolic cysteine pools, considerable amounts of sulphide and presence of OAS in the cytosol, our results suggest that the cytosol is the principal site for cysteine biosynthesis. Subcellular metabolite analysis further indicated efficient transport of cysteine, gamma-glutamylcysteine and glutathione between the compartments. With respect to regulation of cysteine biosynthesis, estimation of subcellular OAS and sulphide concentrations established that OAS is limiting for cysteine biosynthesis and that SAT is mainly present bound in the cysteine-synthase complex.
authors.affiliation: Max Planck Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Potsdam-Golm, France.
authors.forename: Stephan
authors.initials: S
authors.lastname: Krueger
authors.forename: Annette
authors.initials: A
authors.lastname: Niehl
authors.forename: M Carmen
authors.initials: MC
authors.lastname: Lopez Martin
authors.forename: Dirk
authors.initials: D
authors.lastname: Steinhauser
authors.forename: Andrea
authors.initials: A
authors.lastname: Donath
authors.forename: Tatjana
authors.initials: T
authors.lastname: Hildebrandt
authors.forename: Luis C
authors.initials: LC
authors.lastname: Romero
authors.forename: Rainer
authors.initials: R
authors.lastname: Hoefgen
authors.forename: Cecilia
authors.initials: C
authors.lastname: Gotor
authors.forename: Holger
authors.initials: H
authors.lastname: Hesse
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D003545:Cysteine / Q000096:biosynthesis*; D003547:Cysteine Synthase / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology*; D004269:DNA, Bacterial / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D016254:Mutagenesis, Insertional; D009154:Mutation; D018087:Plastids / Q000201:enzymology*; D051050:Serine O-Acetyltransferase / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; D018744:DNA, Plant; D007527:Isoenzymes; C036483:T-DNA; D051050:Serine O-Acetyltransferase; D003547:Cysteine Synthase; D003545:Cysteine