Analysis of cytosolic and plastidic serine acetyltransferase mutants and subcellular metabolite distributions suggests interplay of the cellular compartments for cysteine biosynthesis in Arabidopsis |
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Authors: | STEPHAN KRUEGER ,ANNETTE NIEHL,M. CARMEN LOPEZ MARTIN,DIRK STEINHAUSER,REA DONATH,TATJANA HILDEBRANDT,LUIS C. ROMERO,RAINER HOEFGEN,CECILIA GOTOR,& HOLGER HESSE |
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Affiliation: | Max Planck Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Potsdam-Golm,;Institut de Biologie Moléculaire des Plantes, laboratoire propre du CNRS (UPR 2357) conventionnéavec l'UniversitéLouis Pasteur (Strasbourg 1), 12 rue du Général Zimmer, 67084 Strasbourg CEDEX, France,;Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, Avenida Américo Vespucio, 49, Sevilla 41092, Spain and;Institut für Zoophysiologie, Heinrich-Heine-Universität, Universitätsstrasse 1, 40225 Düsseldorf, Germany |
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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, γ -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. |
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Keywords: | non-aqueous fractionation organelles regulation subcellular sulphur metabolism |
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