Liquid-liquid phase separation around a membrane: Investigating the assembly of the pyrenoid around the thylakoid membrane in Chlamydomonas reinhardtii

• Applicant: Dr. Philipp Girr
• Subject Area: Plant Biochemistry and Biophysics
• Term: from 2021 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 456013262

It is currently a major challenge for humankind to ensure global food security for a growing world population and to fulfil the demands of carbon-neutral energy sources in times of climate change. Critical to addressing this challenge is an increase in crop yields to ensure that increases in food and biofuel production are achieved without further agriculture driven ecosystem loss. One promising approach that is predicted to increase crop yields by up to 60% is the engineering of an algal CO2 concentrating mechanism (CCM) into crop plants. The heart of the algal CCM is a liquid-liquid phase separated organelle within the chloroplast, the pyrenoid. The pyrenoid contains most of the cells Rubisco and is constantly supplied with CO2 by active transport mechanisms. CO2 enters the pyrenoid ultimately through specialised regions of the thylakoid membrane that transverse the pyrenoid, the so-called thylakoid tubules. Even though the thylakoid tubules are important for the CO2 supply and the exchange of metabolites between the pyrenoid and the chloroplast stroma, we basically know nothing about the interaction between the Rubisco containing matrix of the pyrenoid and thylakoid tubules and the biogenesis of the thylakoid tubules. In the proposed project, I will investigate these knowledge gaps in the model organism Chlamydomonas reinhardtii. Through literature and bioinformatic analysis I have identified candidate proteins that could act as tether proteins between the thylakoid tubules and the pyrenoid matrix, and others that are potentially involved the biogenesis of the thylakoid tubules. In the proposed project, I will biochemically analyse the function of those proteins both in vivo and in vitro to elucidate their function. Furthermore, I will use the identified underlying fundamental principles of pyrenoid assembly to guide the engineering of a synthetic CCM system in vitro. Together, the data obtained in the proposed project will guide the engineering of a pyrenoid in crops to increase yields.

• DFG Programme: WBP Fellowship
• International Connection: United Kingdom
• Host: Professor Dr. Luke Mackinder