Sustained Photosynthesis in Tobacco Leaves by Fast CO<sub>2</sub>-Fixing Enzymes Encapsulated in Micro-Compartments

Abstract

Improvement of yield potential in global food crops has hit a breeding road-block which could be solved through genetic engineering. One promising strategy is the introduction of cyanobacterial CO2-concentrating-mechanisms (CCMs) into plant chloroplasts to enhance photosynthesis and yield. CCMs actively accumulate CO2 within specialized microcompartments called carboxysomes, where the enzyme Rubisco rapidly fixes CO2. Here we replaced the endogenous Rubisco large subunit gene with cyanobacterial Form-1A Rubisco and key structural proteins of α- carboxysomes in tobacco chloroplasts. Transformed plants produced purifiable carboxysomes, isometric with those of the source organism Cyanobium marinum. Carboxysomes encapsulated the introduced Rubisco and enabled autotrophic growth at elevated CO2. Our results demonstrate the formation of α-carboxysomes from a minimal gene set, and that cyanobacterial Form-1A Rubisco supports C3 photosynthesis at high CO2. This major advance informs the step-wise construction of fully-functional α-carboxysomes in chloroplasts which, along with other CCM components, are expected to improve crop plant performance.