Condensation of Rubisco into a proto-pyrenoid in higher plant chloroplasts (bioRxiv)

Rubisco is a major enzyme in assimilating CO₂ during photosynthesis. The efficiency of CO₂ assimilation is compromised by a low ratio of CO₂/O₂, especially in C3 plants like rice, wheat and soybean. Algae sequester Rubisco as a condensate in a microcompartment called a pyrenoid within the chloroplast and have a CO₂-concentrating mechanism that delivers CO₂ to the Rubisco within these sites. To address the feasibility of introducing a similar CO₂-concentrating strategy to higher plants, Atkinson et al. expressed a mature EPYC1 (Essential Pyrenoid Component 1; a Rubisco-linking protein) and a plant-algal hybrid Rubisco in Arabidopsis chloroplasts. This expression led to Rubisco condensates, “proto-pyrenoids,” formation in the chloroplast. Further analysis of photosynthetic efficiency and biomass production of the transgenic plants showed no harmful effect. This study opens the possibility for increasing Rubisco CO₂ assimilation efficiency in higher plants by next introducing the algal CO₂ concentration mechanism to pump CO₂ into the proto-pyrenoid. (Summary by Sunita Pathak @psunita980) bioRxiv 10.1101/2020.10.26.354332