In non-cyanogenic species, the main source of cyanide derives from ethylene and camalexin biosyntheses. In mitochondria, cyanide is a potent inhibitor of the cytochrome c oxidase and is metabolized by the β-cyanoalan...In non-cyanogenic species, the main source of cyanide derives from ethylene and camalexin biosyntheses. In mitochondria, cyanide is a potent inhibitor of the cytochrome c oxidase and is metabolized by the β-cyanoalanine synthase CYS-C1, catalyzing the conversion of cysteine and cyanide to hydrogen sulfide and β-cyanoalanine. The hydrogen sulfide released also inhibits the cytochrome c oxidase and needs to be detoxified by the O-acetylserine（thiol）lyase mitochondrial isoform, OAS-C, which catalyzes the incorporation of sulfide to O-acetylserine to produce cysteine, thus generating a cyclic pathway in the mitochondria. The loss of functional OAS-C isoforms causes phenotypic characteristics very similar to the loss of the CYS-C1 enzyme, showing defects in root hair formation. Genetic complementation with the OAS-Cgene rescues the impairment of root hair elongation, restoring the wild-type phenotype. The mitochondria compromise their capacity to properly detoxify cyanide and the resulting sulfide because the latter cannot re-assimilate into cysteine in the oas-c null mutant. Consequently, we observe an accumulation of sulfide and cyanide and of the alternative oxidase, which is unable to prevent the production of reactive oxygen species probably due to the accumulation of both toxic molecules. Our results allow us to suggest that the significance of OAS-C is related to its role in the proper sulfide and cyanide detoxification in mitochondria.展开更多
Cysteine occupies a central position in plant metabolism because it is a reduced sulfur donor moleculeinvolved in the synthesis of essential biomolecules and defense compounds. Moreover, cysteine per se and its deriva...Cysteine occupies a central position in plant metabolism because it is a reduced sulfur donor moleculeinvolved in the synthesis of essential biomolecules and defense compounds. Moreover, cysteine per se and its deriva-tive molecules play roles in the redox signaling of processes occurring in various cellular compartments. Cysteine issynthesized during the sulfate assimilation pathway via the incorporation of sulfide to O-acetylserine, catalyzed byO-acetylserine（thiol）lyase （OASTL）. Plant cells contain OASTLs in the mitochondria, chloroplasts, and cytosol, resultingin a complex array of isoforms and subcellular cysteine pools, in recent years, significant progress has been made inArabidopsis, in determining the specific roles of the OASTLs and the metabolites produced by them. Thus, the dis-covery of novel enzymatic activities of the less-abundant, like DES1 with L-cysteine desulfhydrase activity and SCSwith S-sulfocysteine synthase activity, has provided new perspectives on their roles, besides their metabolic functions.Thereby, the research has been demonstrated that cytosolic sulfide and chloroplastic S-sulfocysteine act as signalingmolecules regulating autophagy and protecting the photosystems, respectively. In the cytosol, cysteine plays an essentialrole in plant immunity; in the mitochondria, this molecule plays a central role in the detoxification of cyanide, which isessential for root hair development and plant responses to pathogens.展开更多
文摘In non-cyanogenic species, the main source of cyanide derives from ethylene and camalexin biosyntheses. In mitochondria, cyanide is a potent inhibitor of the cytochrome c oxidase and is metabolized by the β-cyanoalanine synthase CYS-C1, catalyzing the conversion of cysteine and cyanide to hydrogen sulfide and β-cyanoalanine. The hydrogen sulfide released also inhibits the cytochrome c oxidase and needs to be detoxified by the O-acetylserine（thiol）lyase mitochondrial isoform, OAS-C, which catalyzes the incorporation of sulfide to O-acetylserine to produce cysteine, thus generating a cyclic pathway in the mitochondria. The loss of functional OAS-C isoforms causes phenotypic characteristics very similar to the loss of the CYS-C1 enzyme, showing defects in root hair formation. Genetic complementation with the OAS-Cgene rescues the impairment of root hair elongation, restoring the wild-type phenotype. The mitochondria compromise their capacity to properly detoxify cyanide and the resulting sulfide because the latter cannot re-assimilate into cysteine in the oas-c null mutant. Consequently, we observe an accumulation of sulfide and cyanide and of the alternative oxidase, which is unable to prevent the production of reactive oxygen species probably due to the accumulation of both toxic molecules. Our results allow us to suggest that the significance of OAS-C is related to its role in the proper sulfide and cyanide detoxification in mitochondria.
文摘Cysteine occupies a central position in plant metabolism because it is a reduced sulfur donor moleculeinvolved in the synthesis of essential biomolecules and defense compounds. Moreover, cysteine per se and its deriva-tive molecules play roles in the redox signaling of processes occurring in various cellular compartments. Cysteine issynthesized during the sulfate assimilation pathway via the incorporation of sulfide to O-acetylserine, catalyzed byO-acetylserine（thiol）lyase （OASTL）. Plant cells contain OASTLs in the mitochondria, chloroplasts, and cytosol, resultingin a complex array of isoforms and subcellular cysteine pools, in recent years, significant progress has been made inArabidopsis, in determining the specific roles of the OASTLs and the metabolites produced by them. Thus, the dis-covery of novel enzymatic activities of the less-abundant, like DES1 with L-cysteine desulfhydrase activity and SCSwith S-sulfocysteine synthase activity, has provided new perspectives on their roles, besides their metabolic functions.Thereby, the research has been demonstrated that cytosolic sulfide and chloroplastic S-sulfocysteine act as signalingmolecules regulating autophagy and protecting the photosystems, respectively. In the cytosol, cysteine plays an essentialrole in plant immunity; in the mitochondria, this molecule plays a central role in the detoxification of cyanide, which isessential for root hair development and plant responses to pathogens.
