Thiol redox regulation for efficient adjustment of sulfur metabolism in abiotic stress acclimation.

Sulfur assimilation and sulfur metabolism are tightly controlled at the transcriptional, posttranscriptional and posttranslational level in order to meet the demand for reduced sulfur in growth and metabolism. These regulatory mechanisms coordinate the cellular sulfhydryl supply in particular with carbon and nitrogen assimilation. Redox homeostasis is an important cellular parameter intimately connected to sulfur by means of multiple thiol modifications. Posttranslational thiol modifications such as disulfide formation, sulfenylation, S-nitrosylation, persulfidation and S-glutathionylation allow for versatile switching and adjustment of protein functions. This update focuses on redox-regulation of enzymes involved in the sulfur assimilation pathway, i.e. adenosine 5`phosphosulfate reductase (APR), adenosine 5'-phosphosulfate kinase (APSK) and y-glutamylcysteine ligase (GCL). The activity of these enzymes is adjusted at the transcriptional and posttranslational level in dependence on physiological requirements and the state of the redox and reactive oxygen species network which is tightly linked to abiotic stress conditions. Hormone-dependent fine tuning contributes to regulation of sulfur assimilation. Thus the link between oxylipin signalling and sulfur assimilation was substantiated by identification of the so called COPS module in the chloroplast with its components cyclophilin 20-3, O-acetylserine thiol lyase, 2-cysteine peroxiredoxin and serine acetyl transferase. A detailed understanding of regulation has emerged which realises the fine-tuned adjustment of sulfur assimilation both under regular and abiotic stress conditions.