Scientists have been able to fix a natural flaw in photosynthesis, which resulted in increased plant productivity by an incredible 40 percent compared to their wild relatives. They’ve achieved this by borrowing a more efficient photorespiration approach from lower organisms.
Photosynthesis is the chemical reaction that enables green plants harness the energy from sunlight and carbon dioxide turning it into food, and this new upgrade could result in enough calories to help feed another 200 million people on our planet, from the same volume of crops.
As at the time of this writing, the fix has only been applied to tobacco plants, so while we might be a long way from applying it into other staple crops, it is still an incredibly promising first step.
So what is this ‘glitch’ that needed fixing? It’s a little-known step in photosynthesis known as photorespiration.
Photorespiration is a wasteful pathway that competes with the Calvin cycle. It begins when rubisco acts on oxygen instead of carbon dioxide.
“We could feed up to 200 million additional people with the calories lost to photorespiration in the Midwestern US each year,” says principal investigator Donald Ort from the University of Illinois Carl R. Woese Institute for Genomic Biology. “Reclaiming even a portion of these calories across the world would go a long way to meeting the 21st century’s rapidly expanding food demands.”
In other to understand what goes wrong in photosynthesis, you need to understand a little about the haphazard process of evolution. Looking at the immortal words of Dr Ian Malcolm in the sci-fi classic Jurassic Park, “Life finds a way“. But what he failed to mention is that sometimes that way is an inefficient hot mess.
To be fair, evolution does the best that it can given the circumstance. Like a student looking forward to the summer break, it does just enough to pass. Anything more is a wasted effort, after all.
For very many plants, this is including legumes like soybea and cereals like rice, when it comes to photosynthesis, it’s a bare pass. We’re talking a begrudging D.
One of the most clumsy parts is a key step involving the enzyme ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO). RuBP oxygenase-carboxylase (rubisco), a key enzyme in photosynthesis, is the molecular equivalent of a good friend with a bad habit. In the process of carbon fixation, rubisco incorporates carbon dioxide (CO2) into an organic molecule during the first stage of the Calvin cycle. Rubisco is so important to plants that it makes up 30% or more of the soluble protein in a typical plant leaf.
But rubisco also has a major flaw: instead of always using CO2 as a substrate, it sometimes picks up O2 instead.
Not only is this a wasted opportunity, the result of this glitch reaction is glycolate and ammonia – two toxic compounds that need to be swiftly dealt with before they cause too much damage.
Fortunately for plants they evolved a way to rid themselves of this poison, called photorespiration. As such they don’t mind spending a portion of their energy on this vital recycling process if it helps them survive. But when it comes to growing them as a food source, humans certainly do.
“It costs the plant precious energy and resources that it could have invested in photosynthesis to produce more growth and yield,” says lead author and molecular biologist Paul South with the US Department of Agriculture Agricultural Research Service.
Rice, wheat, and soybeans are all victims of this scourge toxic scourge. Not only do they happen to be three of the four crops our world’s population relies on for most our calories, we can expect their yield to drop in the future thanks to global warming. The reason is that the enzyme RuBisCO has even more trouble distinguishing between carbon dioxide and oxygen as the temperature gets hotter, thereby causing more photorespiration.
Over the years, scientists have tried several ways to force plants to avoid this need to detox. Many of these methods have involved finding the most efficient photorespiration approaches taken by other organisms, including various algae and bacteria. This latest effort is called Realizing Increased Photosynthetic Efficiency (RIPE), and its approach was to select genes from elsewhere and test them out. A handful came from the bacterium E. coli’s glycolate oxidation pathway. A second version used a gene for catalase also from E. coli, and some for a glycolate oxidase and malate synthase from plants. Subject number three used a plant malate synthase gene and a green algal gene for glycolate dehydrogenase. These were used in conjunction with other genetic tweaks to find the most energy efficient pathway among 17 different constructs. The third photorespiration pathway was the one that stood out from the rest in final results, with metabolic activity surging more than 40 percent compared with controls. This gained energy translates into bigger yields. It remains to be seen whether these same efficiency boosts will be translated to other crops, but the researchers are working on it. Life doesn’t always find a way. But if we’re to get food to where it’s needed in the future, science will have to.
This research was published in Science.Tags: Food, Photorespiration, Photosynthesis
Follow us on Twitter
Call Hours: 9am - 5pm (Mon - Fri)
Copyright © 2019 The Paraklet LLC. All Names, Acronyms and Trademarks displayed on this website are those of their respective owners.