It wouldn’t be an understatement to say we owe all the wonders of life to photosynthesis – the ability of plants and certain bacteria to convert CO2 into energy (sugars) and food. Scientists have for some time attempted to enhance photosynthesis through genetic manipulation, but it’s only recently that we’re beginning to see these efforts take form. The most recent breakthrough was made by a team of British and American biologists who report they’ve successfully infused tobacco plants with bacterial genes – a first step towards engineering crops that grow faster, offer higher yields and use less fertilizers.
Better photosynthesis, more food
Cyanobacteria – single-celled organisms also known as blue algae – are far more better at converting CO2 to useful energy than plants. Part of the reason is that the bacteria use an upgraded version of an enzyme called rubisco, which is the protein that converts CO2 into sugar, and is possibly the most abundant protein on Earth. About half of all the soluble proteins found in leaves are rubisco.
In plants, however, rubisco isn’t that efficient and scientists have been trying to find ways to boost it for some time. If such an attempt were to be proven entirely successful, then crops with the equivalent bacterial photosynthesis ability would cut fertilizer needs and increase crop production by 35 and 60 percent. But researchers at Cornell University, USA and Rothamsted Research, UK claim they’ve managed to solve one piece of the puzzle: they’ve modified tobacco plants that produce functional rubisco from the cyanobacterium Synechococcus elongatus.
This wasn’t an easy job, though. While previous attempts focused on swapping bacterial genes that code for the turbocharged rubisco, the team also made other genetic substitutions that encode proteins that manufacture the rubisco. The modified plants confer CO2 into sugar faster than normal tobacco, a sign that photosynthesis had been sped up and that the researchers are heading in the right direction.
Yet they still have their work cut out for them. While the photosynthesis is more efficient, the plants themselves grew significantly slower. The researchers report:
“We grew our [genetically engineered] plants in a CO2 elevated environment” with more 22 times the amount of normal amount of the gas, “and they still were growing slightly slower than the normal type plants.”
While the algal rubisco makes the photosynthesis more efficient, the tobacco plant wasn’t completely engineered to mimic the whole process the bacteria use. Namely, cyanobacteria employ β-carboxysome shell proteins that ward off oxygen, creating a tiny, CO2-rich environments for their rubisco. Normal plants on the other hand lack this shell and consequently adapted by using a form of rubisco that is slower and less efficient, but which none the less is also capable of picking CO2 in favor of O2. In the case of our modified tobacco plant, the Rubisco is bacterial, but without the shell, a lot of energy is wasted on reacting with oxygen.
Obviously, researchers are concentrating on how to integrate the shell with the bacterial rubisco. So far, developments have been promising since the same team engineered tobacco plants that could generate carboxysome-like structures a while back. Integrating the findings of the two bodies of research might finally take food production to a new level.
While genetically modified plants, fertilizers and pesticides have made crop yields go a long way, the momentum sparked a couple of decades ago is steadily running out. Soon enough, we’ll have to find new ways to increase food production per unit area to keep up with an ever expanding population. Tweaking photosynthesis may be just one in many such efforts.