"What makes a racehorse fast?" Exploring the role of photosynthetic and metabolic performance in growth of photosynthetic cells

• Applicants: Professor Dr. Zoran Nikoloski, Ph.D.; Professor Dr. Michael Schroda
• Subject Area: Plant Biochemistry and Biophysics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 517516852

Supplying the rapidly growing world population will require an increase in food production in the near future. Increasing the photosynthetic performance of crop plants is considered a promising approach here, as it is far from its biological limits. Particularly high photosynthetic outputs often occur in organisms that have to cope with special stress conditions. For example, Chlorella ohadii, a green microalga recently isolated from a desert biological soil crust, exhibits the fastest growth rate and highest photosynthetic rate per chlorophyll ever reported for a photosynthetic organism. The question arises, what defines the upper limit for the growth of a photosynthetic cell? We have already shown that the high growth rates of C. ohadii result from its high metabolic flexibility. Accordingly, the main goal of this project is to decipher bottlenecks in the metabolic pathways of photosynthetic cells that limit the growth of algae and plants. This goal will be achieved by the following approaches: first, we want to comparatively investigate the metabolic rates (fluxes) in the central and photosynthetic metabolism of very fast (C. ohadii) and slower (C. reinhardtii) growing microalgae under different conditions to identify reactions or combinations of reactions that could be causative for the different growth rate ("potential bottlenecks"). Second, we aim to determine the absolute concentrations of key enzymes that catalyze the most important reactions in the central and photosynthetic metabolic pathways. This will allow us to determine their in vivo kcat levels to better assess metabolite fluxes based on metabolic models. Third, we will use transgenic approaches to test whether and which of the identified reactions limit the growth of the slower-growing, genetically accessible alga C. reinhardtii. For this, we want to replace C. reinhardtii genes with orthologs from the fast-growing alga C. ohadii or alter the expression of native C. reinhardtii genes. Finally, we aim to investigate the effects of these metabolic interventions on growth and photosynthetic rates, as well as metabolite fluxes and carbon allocation patterns in the metabolic network of the engineered strains. In the long term, the knowledge gained from the microalgal systems will be used to modify crops to produce higher yields.

• DFG Programme: Research Grants
• International Connection: Israel
• International Co-Applicant: Professor Dr. Haim Treves, Ph.D.