Metabolic coupling of plastidic and cytosolic pools of low-molecular weight thiols via members of the CRT-like transporter (CLT) family

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Glutathione is the most abundant low molecular weight thiol in virtually all living organisms and has essential functions in cellular redox homeostasis and environmental signaling. In Arabidopsis thaliana, the two step biosynthetic pathway for glutathione is compartmentalized between plastids and cytosol with the first enzyme, glutamate-cysteine ligase (GSH1), being localized exclusively in the plastids and the second enzyme, glutathione synthase (GSH2), being expressed in both compartments. Coupling of the two glutathione pools is mediated by the recently identified chloroquine-resistance transporter like transporters (CLTs), which are the first functionally characterized members of the plant drug/metabolite exporter family. In this project, the protein structure and the characterization of the transport properties of all three Arabidopsis CLTs will be investigated in vivo as well as in vitro in heterologous expression systems and reconstituted liposomes. The in vivo function of CLTs for bidirectional transport between plastids and cytosol will be analyzed through compartment-specific reconstitution of the glutathione biosynthetic pathway in a mutant background. Misexpression of GSH1 in the cytosol will also provide novel information about the regulation of GSH1 activity. In vivo imaging of the glutathione redox potential with redoxsensitive GFP probes will further resolve the dynamics of the glutathione redox buffer under exposure to abiotic and biotic stress at subcellular level and help elucidating the role of glutathione in activating the immune response in plants.