Engineering α-carboxysomes into plant chloroplasts to support autotrophic photosynthesis.

The growth in world population, climate change, and resource scarcity necessitate a sustainable increase in crop productivity. Photosynthesis in major crops is limited by the inefficiency of the key CO 2 -fixing enzyme Rubisco, owing to its low carboxylation rate and poor ability to discriminate between CO 2 and O 2 . In cyanobacteria and proteobacteria, carboxysomes function as the central CO 2 -fixing organelles that elevate CO 2 levels around encapsulated Rubisco to enhance carboxylation. There is growing interest in engineering carboxysomes into crop chloroplasts as a potential route for improving photosynthesis and crop yields. Here, we generate morphologically correct carboxysomes in tobacco chloroplasts by transforming nine carboxysome genetic components derived from a proteobacterium. The chloroplast-expressed carboxysomes display a structural and functional integrity comparable to native carboxysomes and support autotrophic growth and photosynthesis of the transplastomic plants at elevated CO 2 . Our study provides proof-of-concept for a route to engineering fully functional CO 2 -fixing modules and entire CO 2 -concentrating mechanisms into chloroplasts to improve crop photosynthesis and productivity.