Novel perspectives on cysteine-dependent enzymes and processes in photosynthetic organisms

Present in various subcellular compartments, cysteine is the major source of reduced sulfur and thus represents a key metabolite for various biosynthetic pathways as well as for redox homeostasis as a component of glutathione. As photosynthetic organisms assimilate inorganic sulfate and reduce it into sulfide before its incorporation into cysteine, there are strong relationships between cysteine homeostasis and all pathways involved in its synthesis and utilization. Over the last decade, cysteine degradation leading to hydrogen sulfide release has been linked to different physiological responses to both abiotic and biotic stresses. In this review, we summarize current knowledge about cysteine homeostasis, cysteine signaling in immunity and cysteine-dependent sulfur trafficking. We also illustrate the importance of cysteine signaling through the synthesis of hydrogen sulfide by describing the diversity of cysteine desulfhydrases in photosynthetic organisms and by discussing their roles in plant physiology.