Calcium-dependent phosphorylation as a regulator of metabolic processes in chloroplasts

• Applicant: Professorin Dr. Ute Carla Vothknecht
• Subject Area: Plant Physiology
• Term: from 2013 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 233379228

Plant development and adaptation is determined by genetically inherited programs that are fine-tuned by short-term responses to external and internal stimuli. In eukaryotes, calcium is an important second messenger and many abiotic and biotic signals are transduced into a cellular response by changes in calcium concentration. To facilitate calcium signalling, calcium spikes are produced by calcium fluxes from extracellular and intracellular stores, thereby allowing a temporary and spatially controlled regulation. Changes in calcium concentration are perceived by calcium sensors, such as calmodulin, that initiate specific cellular responses either directly or by interaction with down-stream targets. Since many metabolic processes take place in chloroplasts, their integration into the encompassing regulatory networks of the cell is essential to ensure that organellar function is carefully balanced in accordance with the metabolic requirements of the whole plant. Experimental evidence has indicated the existence of calcium-dependent regulatory circuits in chloroplasts. Changes in calcium concentration have been observed under different conditions and several calcium-binding proteins and calmodulin targets have been identified. However, the full impact of calcium on organellar function is not very well under-stood. Calcium/calmodulin was implicated in the regulation of several chloroplast proteins, including NAD-kinase, the only source for chloroplast NADP synthesis and thus important for the maintenance of a proper NAD/NADP balance. We have also obtained direct experimental evidence for calcium-dependent protein phosphorylation in chloroplasts. Target proteins include transketolase, a central constituent of the Calvin-Benson-Bassham cycle and the phentose phosphate pathway, and thereby of carbon metabolism. Within this project we want to analyse the influence of calcium on chloroplast function. We want to characterize the calcium-dependent phosphorylation of transketolase (and eventually other chloroplast proteins) to elucidate the impact of this post-translational modification on organellar carbon metabolism. Furthermore, we want to investigate the role of calcium/calmodulin regulation of chloroplast NAD-kinase for organellar redox-balance and metabolism. A systematic analysis of specific interactions between calcium sensors and their target proteins will unravel the connections within the organellar calcium-network that affect specific organellar functions.

• DFG Programme: Research Grants