Can bioengineers produce plants that absorb more carbon dioxide?

 With dire health consequences predicted to follow global climate change,  scientists are rushing to invent new solutions to the problem rather than rely on a global political system that seems unlikely to budge. At the root of this drama is carbon dioxide (CO2) – a greenhouse gas so stable that it is nearly impossible to pull out of the atmosphere. Even to this day, the only technology that reliably works to capture carbon dioxide evolved 3.4 billion years ago – photosynthesis. It may end up that this natural chemistry becomes the climate’s best hope.

This week witnessed a landmark for the Earth’s climate – the concentration of atmospheric carbon dioxide passed 400 ppm for the first time in millions of years. This milestone has alarmed the vast majority of the world’s educated public – especially since no viable carbon-reducing technology has yet to be invented.

In the face of this challenge, some scientists are looking to improve upon nature’s own carbon-capturing technique- photosynthesis.

The idea of tinkering with the chemistry of photosynthesis has tantalized scientists for decades. By increasing the carbon-capturing ability of plants, more carbon dioxide would be removed from the atmosphere and diverted into improving crop yields.

Despite the inherent allure of this idea, progress in the field has been interminably slow, almost to the point of non-existence.

Why hasn’t science succeeded yet?

Nature has used 3.4 billion years to fine tune the gears of the photosynthetic machine. Because of this, it is one of the most remarkable processes ever discovered, and one of the most complicated. Through photosynthesis, plants are able harness energy from the sun to propel a chemical reaction that produces sugar from atmospheric CO2, all while contained in a microscopic reaction container.

Because attempts to recreate the photosynthetic process using artificial technology abjectly failed, scientists instead decided to focus on improving different parts of the process, namely the enzyme known as Rubisco (RuBisCo, or D-ribulose 1,5-Bisphosphate carboxylase/oxygenase). Rubisco catalyzes the first step in carbon dioxide fixation, whereby one molecule of carbon dioxide is chemically modified and assimilated into the Calvin cycle, eventually turning into the sugar known as fructose.

Even though nature has had billions of years to perfect Rubisco, it is still one of the most complicated and least efficient enzymes known to science. Because of its inefficiency, Rubisco is produced in massive quantities by plants, making it the most abundant protein on Earth.

Up to this point, all attempts to make Rubisco more efficient have also failed.

Yet, in a great leap forward for plants and humans alike, a recent experiment published in Nature reported on the first semi-synthetic Rubisco.

Long ago, a different type of Rubisco was discovered in single celled blue-green algae (called cyanobacteria) – this type was found to be more efficient than the most common form found in plants such as rice, barley, oats, potatoes, and trees.

Where other researchers have repeatedly failed to introduce this efficient form of Rubisco into common plants, these scientists succeeded in creating tobacco plants that could capture more carbon dioxide.

The key to their success came from the inclusion of a certain protein that could chaperone the newly created Rubisco. This molecular supervisor ensures that Rubisco is formed properly by the cell’s machinery.

These new created tobacco plants could grow in high carbon concentrations and could fix more carbon dioxide per unit of enzyme than their normal counterparts. All this was observed even though other crucial parts of the cyanobacteria system were missing.

Results from this experiment open the door to a new world of climate engineering, where common crops could be made to soak up unprecedented levels of carbon dioxide, and perhaps lead to larger crop yields.

But then again, where does the global community stand on GMOs?

Image: Tobacco plants with bioengineered RuBisCo compared to natural plants. (Image credit: pubmed)

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