Regulation of cysteine partitioning into translation and stress responses.

• Applicants: Professor Dr. Rüdiger Hell; Markus Wirtz, Ph.D.
• Subject Area: Plant Physiology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 544882710

Sulfur metabolism in plants is vital due to the manifold functions of reduced sulfur in general metabolites. Many environmental stimuli strongly affect the sulfur assimilation pathway since stress-related compounds such as glutathione are specifically required upon biotic or abiotic stresses. The central compound that provides reduced sulfur for metabolite and protein syntheses is cysteine. The rate of cysteine formation is mainly controlled by the regulatory cysteine synthase complexes in plastids and the cytosol. Our previous work provided evidence that genetic down-regulation of glutathione synthesis results in release of cysteine that is invested into growth. Here we hypothesize that partitioning of the critical compound cysteine can adapt to either growth promoting or stress defense related processes. We suggest to challenge cysteine partitioning by growth conditions of either limited sulfate supply or enhanced demand, the latter triggered by consumption of glutathione for phytochelatin synthesis to scavenge cadmium. Changes in partitioning and compartment-specific synthesis of protein will be monitored by metabolite partitioning via 35S tracing and translatome and steady-state proteomics. It is expected that the altered partitioning is accomplished by a dynamic re-organization of the major compartmental sites of cysteine synthesis, i.e. plastids and the cytosol. To simulate altered partitioning a novel over-production approach consisting of a constitutively activated cysteine synthase complex has been developed that eliminates the endogenous sensing function of the complex. This system will be implemented in either plastids or the cytosol and is based on the constitutive activation of the cysteine synthase complex, resulting in enhanced local cysteine production. According to this hypothesis, enhanced demand would favor de novo cysteine production inside the chloroplast to push glutathione production. Correspondingly, we propose that limited sulfur supply would redirect the partitioning of cysteine from glutathione to protein synthesis in the cytosol to maintain growth. By applying physiologically and environmentally relevant stress conditions, it will be possible to verify the fundamental importance of cysteine partitioning for stress acclimation in plants.

• DFG Programme: Research Grants