Towards deciphering dynamic light-induced H2O2 formation in chloroplasts and its transfer to the cytosol and nucleus

• Applicant: Professor Dr. Andreas Meyer
• Subject Area: Plant Physiology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 552784813

Chloroplasts as endosymbiotic organelles rely on the nuclear genome to be served with most of their proteins. With this, plastid development and gene expression linked to stress-responsive adaptive processes are largely under nuclear control. To ensure an appropriate gene expression and translation according to demand, multiple retrograde control mechanisms have evolved by which chloroplasts communicate their current physiological state to the nucleus. Among these, redox-dependent signal transduction may provide the most direct link between the core photosynthetic machinery and gene expression upon illumination. During photosynthesis, reactive oxygen species (ROS), such as superoxide (O2-) and hydrogen peroxide (H2O2), are generated as inevitable by-products. H2O2 has long been considered as a retrograde signal but evidence for this so far is largely indirect and information about the light-dependent dynamics in H2O2 in chloroplasts and the cytosol is missing. Genetically encoded biosensors, such as HyPer7 for H2O2 and Grx1-roGFP2 for the glutathione redox potential (EGSH) offer opportunities to study these parameters in live cells, but applying these sensors in combination with appropriate illumination has been challenging. For this project, we developed a novel setup with automatized internal illumination of plants inside a fluorescence plate reader such that the delay between illumination and actual multiplexed measurements is reduced to a minimum. Targeting of different biosensors to both, the chloroplast stroma and the cytosol now enables to follow light-induced changes in H2O2 and EGSH in both compartments. With the ultimate goal of decoding H2O2 signals from chloroplasts, these measurements will subsequently be complemented with studies of light-induced redox dynamics of the nucleoplasm and variations of the redox state of the NADP pool. Inevitably, H2O2 signalling is affected by multiple factors, such as its production site after superoxide dismutation, its detoxification in chloroplasts, export of H2O2 across the chloroplast envelope, and detoxification in the cytosol. Detoxification in the cytosol by different peroxidases in conjunction with different oxidoreductases like thioredoxins and glutaredoxins may allow transmission of H2O2 signals to target proteins like transcription factors. Dynamic analysis of the respective parameters in intact Arabidopsis plants in combination with pharmacological and genetic interference is expected to provide novel information that will help to decode H2O2-dependent retrograde signalling. The information gained from this project is expected to provide new ideas for the development of plants with increased stress resistance.

• DFG Programme: Research Grants
• Co-Investigator: Dr. José Manuel Ugalde