title: The role of compartment-specific cysteine synthesis for sulfur homeostasis during H2S exposure in Arabidopsis.
abstract: Sulfide is the end-product of assimilatory sulfate reduction in chloroplasts. It is then used by O-acetylserine(thiol)lyase (OAS-TL) to produce cysteine, the source of reduced sulfur in plants. While its formation in chloroplasts is essential for plant metabolism, sulfide is also a potent toxin mainly targeting respiration in mitochondria. Here, the application of sublethal concentrations of sulfide to Arabidopsis thaliana was used to by-pass assimilatory sulfate reduction, resulting in down-regulation of most genes of the pathway. The dualism of sulfide as substrate and toxin was investigated using knock-out mutants of the chloroplast-, mitochondrion- and cytosol-targeted OAS-TL isoforms. Surprisingly, growth retardation due to intoxication by sulfide was independent of the presence or absence of the three OAS-TL isoforms, indicating rapid exchange towards sulfur homoeostasis between the compartments. Cysteine, glutathione and sulfate, and less so S-sulfocysteine, were identified as major sinks for excess sulfide in wild-type plants. Additionally, the concentration of thiosulfate increased 1,000-fold, pointing towards a significant function of thiosulfate formation during H2S exposure. Synthesis of cysteine in the cytosol was found to be particularly important for accumulation of sulfite, sulfate and thiosulfate, indicating an important role for cytosolic OAS-TL for the re-oxidation of sulfide. The results show that thiosulfate and sulfate accumulation is strongly linked to cytosolic cysteine synthesis and that scavenging of sulfide by cysteine synthesis enhances sulfur compound accumulation. However, lack of cysteine synthesis in a subcellular compartment has no crucial consequences for toxicity and subsequent growth retardation.
authors.affiliation: Centre for Organismal Studies Heidelberg, Department of Plant Molecular Biology, University of Heidelberg, D-69120 Heidelberg, Germany The Hartmut Hoffmann-Berling International Graduate School of Molecular and Cellular Biology (HBIGS), University of Heidelberg, D-69120 Heidelberg, Germany Present address: CSIRO Agriculture Flagship, Black Mountain Laboratories, Canberra, ACT 2601, Australia.
authors.forename: Hannah
authors.initials: H
authors.lastname: Birke
authors.affiliation: Centre for Ecological and Evolutionary Studies, University of Groningen, 9747 Groningen, The Netherlands.
authors.forename: Luit J
authors.initials: LJ
authors.lastname: De Kok
authors.affiliation: Centre for Organismal Studies Heidelberg, Department of Plant Molecular Biology, University of Heidelberg, D-69120 Heidelberg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Wirtz
authors.affiliation: Centre for Organismal Studies Heidelberg, Department of Plant Molecular Biology, University of Heidelberg, D-69120 Heidelberg, Germany ruediger.hell@cos.uni-heidelberg.de.
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Hell
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism; D019757:Carbon-Oxygen Lyases / Q000378:metabolism; D002451:Cell Compartmentation / Q000187:drug effects*; D003545:Cysteine / Q000096:biosynthesis*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant; D006706:Homeostasis / Q000187:drug effects*; D006862:Hydrogen Sulfide / Q000494:pharmacology*; D008954:Models, Biological; D063245:Plant Development / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012995:Solubility; D013438:Sulfhydryl Compounds / Q000378:metabolism; D013455:Sulfur / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D012333:RNA, Messenger; D013438:Sulfhydryl Compounds; D013455:Sulfur; C018725:O-acetylhomoserine (thiol)-lyase; D019757:Carbon-Oxygen Lyases; D003545:Cysteine; D006862:Hydrogen Sulfide
keywords: Arabidopsis; Hydrogen sulfide toxicity; O-Acetylserine(thiol)lyase; S-sulfocysteine; Sulfur assimilation; Thiosulfate