Scientists have genetically engineered a tobacco plant to contain a cyanobacterial variant of a crucial photosynthetic enzyme, raising hopes that this strategy could someday be used to increase crop yields (Nature 2014, DOI: 10.1038/nature13776).
The ubiquitous enzyme Rubisco converts CO2 into sugar during photosynthesis, but in plants, it’s slow and inefficient. A faster Rubisco would mean faster photosynthesis, and potentially higher crop yields—something that might help feed the planet’s growing population.
In contrast with plants, photosynthetic cyanobacteria not only contain more efficient variants of Rubisco, they also speed up photosynthesis with a collection of CO2 pumps and other cellular machinery, together known as the CO2-concentrating mechanism (CCM). CCM works by increasing the levels of CO2 surrounding the Rubisco enzyme. Thus, researchers have considered cyanobacteria a possible focus for the genetic modification of plants.
Rubisco is a complex enzyme, and so far, scientists have failed to substitute cyanobacterial versions for the natural versions in plants. But now, a team led by Maureen Hanson, professor of molecular biology and genetics at Cornell University, has created tobacco plants with the gene for Rubisco found in the cyanobacterium Synechococcus elongatus. Work by collaborator Martin Parry’s group at Rothamsted Research, in England, showed that the engineered plants had higher rates of CO2 conversion compared with a control group.
Nevertheless, further engineering will be required to assemble the complete cyanobacterial CCM in plants. To that end, Hanson’s group has also engineered precursors to a CCM subcellular container, known as a carboxysome, into tobacco plants.
“This is a major step forward” in the grand challenge of redesigning plants’ photosynthetic machinery to harness the full potential of cyanobacterial Rubisco, says Spencer Whitney, an associate professor in the College of Medicine, Biology & Environment at Australian National University, Canberra. Whitney’s lab is also pursuing the transplantation of more efficient versions of Rubisco into plants.
“This work is a milestone on the road to boosting plant efficiency,” add G. Dean Price and Susan M. Howitt, also at Australian National University, in a perspective accompanying the paper. “The advance can be likened to having a new engine block in place in a high-performance car engine—now we just need the turbocharger fitted and tuned.”