Understanding stromal NAD(H) metabolisms and its physiological relevance for C3 photosynthesis

• Applicant: Professor Dr. Hans-Henning Kunz
• Subject Area: Plant Biochemistry and Biophysics ; Plant Physiology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 573916469

Cellular metabolism greatly depends on the two highly similar nicotinamide adenine dinucleotides NAD or NADP. Both molecules act as electron donors or acceptors for dehydrogenases, a specific group of oxidoreductases. Most dehydrogenases accept only one type of co-enzyme, in part to maintain separate NAD(H) and NADP(H) pools. Photosynthesis located in the plant chloroplast has been assumed to utilize primarily NADP(H) since electrons released at photosystem I are used to reduce NADP. However, our own research and work by others have found lately that strictly NAD(H)-dependent enzymes are active in illuminated chloroplasts, too. Using PHOSPHOGLYCERATE DEHYDROGENASE3 (PGDH3) as a first example we show that NAD(H) is also critical for full photosynthetic efficiency, especially under dynamic light conditions as they occur in nature. Our long-term mission is to gain a systematic understanding of the chloroplast’s NAD(H) metabolism and its interactions with the far-better known NADP(H) pool. Through the research proposed here, we will reach the next step of this multi-year program by a) gaining mechanistic insights into why only the PGDH3 isoform, is critical for C3 photosynthesis; b) determining the contribution of dual-coenzyme specific GLYCERALDEHYDE 3-PHOSPHATE DEHYDROGENASE (GAPDH) to the chloroplast’s diurnal NADH metabolism; and c) revealing the importance of the NAD-specific malate valve route for indirect electron export. Ergo, this project will aid a quantitative overview on reactions that deliver diurnal NADH to fuel the chloroplast malate valve and their physiological significance for C3 photosynthesis.

• DFG Programme: Research Grants