Carboxysome encapsulation of the CO2-fixing enzyme Rubisco in tobacco chloroplasts (Nature Comms.)

One of the fundamental challenges facing terrestrial plants occurs when CO₂ levels are depleted at Rubisco, causing its inefficient oxygenase activity to dominate. Some plants minimize this problem by adding a carbon-fixing step upstream of Rubisco, and various algae and cyanobacteria sequester Rubisco into compartments such as carboxysomes into which they pump CO₂. Engineering plants to produce the carboxysome / CO₂ pump should enable them to operate with greater water-use efficiency (due to less need to continually open their stomata) and greater nitrogen-use efficiency (due to less need to synthetize large amounts of Rubisco).  Long et al. describe their efforts to produce Rubisco-sequestering carboxysomes in tobacco chloroplasts. Surprisingly, they were able to achieve this by introducing only a subset of the genes involved in carboxysome formation in cyanobacteria. Because they replaced tobacco’s own Rubisco with the low-CO₂ specificity cyanobacteria enzyme, the resulting plants required elevated CO₂; this limitation should be overcome by the next engineering step in which the CO₂ pump is introduced. (Summary by Mary Williams) Nature Comms. 10.1038/s41467-018-06044-0