Molecular approaches towards control of sulfur flux in plants through selective deregulation of cysteine synthase complexes

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Sulfur assimilation and cysteine biosynthesis in plants are part of the regulatory network of primary assimilation pathways that govern plant fitness and crop production. Protein complexes of cysteine synthase exist in three cellular compartments and are believed to act as regulators of primary sulfur metabolism via reversible protein-protein interaction. The aim of the project is a targeted deregulation of the formation of cysteine synthase complexes in specific compartments to study the consequences of such manipulations in planta. This will be achieved in three stages: An 'in silico' stage will include detailed analyses of the existing structural data of the two subunits of the cysteine synthase complex and the design of polypeptide candidates interfering with the interaction of subunits. During an 'in vitro' stage, the functionality of the designed peptides will be verified by biophysical and biochemical methods using recombinant purified forms of the subunits. The 'in vivo' stage will include transformation of tobacco with the pre-selected constructs and identification of genotypes with deregulated cysteine synthesis in mitochondria and chloroplasts. This will enable us to track down the structural basis of regulation within the cysteine synthase complex and its role in regulation of sulfur flux.