Topology of the redox network during induction of photosynthesis as revealed by time-resolved proteomics in tobacco

Photosynthetically produced electrons provide energy for various metabolic pathways, including carbon reduction. Four Calvin-Benson cycle enzymes and several other plastid proteins are activated in the light by reduction of specific cysteines via thioredoxins, a family of electron transporters operating in redox regulation networks. How does this network link the photosynthetic chain with cellular metabolism? Using a time-resolved redox proteomic method, we have investigated the redox network in vivo during the dark-to-low light transition. We show that redox states of some thioredoxins follow the photosynthetic linear electron transport rate. While some redox targets have kinetics compatible with an equilibrium with one thioredoxin (TRXf), reduction of other proteins shows specific kinetic limitations, allowing fine-tuning of each redox- regulated step of chloroplast metabolism. We identified five new redox-regulated proteins, including proteins involved in Mg2+ transport and O-1(2) signaling. Our results provide a system-level functional view of the photosynthetic redox regulation network.

Automated summary

Photosynthetically produced electrons are used to activate Calvin-Benson cycle enzymes and other plastid proteins by reducing specific cysteines via thioredoxins. The redox network in chloroplasts connects the photosynthetic chain with cellular metabolism, allowing fine-tuning of each redox-regulated step. New redox-regulated proteins, involved in Mg2+ transport and signaling, were identified, providing a system-level functional view of the photosynthetic redox regulation network.