All that oxygen you enjoy breathing doesn’t just appear magically in the atmosphere. Earth is livable because plants around the globe pump out oxygen as a byproduct of photosynthesis, and some of them become tasty food crops in addition. However, photosynthesis isn’t perfect despite many eons of evolutionary refinement. Scientists from the University of Illinois have worked to correct for a flaw in photosynthesis, and that could improve crop yields by as much as 40 percent.
At the heart of the new research is a process in plants called photorespiration, which is not so much part of photosynthesis as it is a consequence of it. Like many biological processes, photosynthesis doesn’t work correctly 100 percent of the time. In fact, one of the main reactions in photosynthesis is only about 75 percent effective. The change comes in the process that plants undertake because of that inefficiency.
In photosynthesis, plants take water and carbon dioxide and process it to create sugars (food) and oxygen. Plants don’t need the oxygen, so it gets expelled. Happily, we do need oxygen, and we exhale carbon dioxide.
The problem addressed in the new study is with an enzyme called ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO). This protein complex attaches a carbon dioxide molecule to ribulose-1,5-bisphosphate (RuBP). Over the ages, Earth’s atmosphere has become more oxygenated, and that means RuBisCO has to cope with more oxygen molecules mixed in with carbon dioxide. About a quarter of the time, RuBisCO grabs an oxygen molecule by mistake, and that has consequences inside a plant.
When RuBisCO screws up, plants are left with toxic byproducts like glycolate and ammonia. It takes energy to process these compounds (through photorespiration), which is added to the energy loss from photosynthesis inefficiency. The study authors note that rice, wheat, and soybeans all suffer from this glitch, and RuBisCO gets even less accurate as temperatures rise. That means food supplies could go down as global warming becomes more severe.
The fix is part of a program called Realizing Increased Photosynthetic Efficiency (RIPE), and it relies on the introduction of new genes that improve growth. Usually, photorespiration takes a circuitous and complex route through three different cellular organelles. It consumes ATP (the energy currency of cells) that should be going to making the plant larger and stronger. RIPE focuses on making photorespiration quicker and more energy efficient.
The team developed three alternate pathways using new genetic sequences. They optimized these pathways across 1,700 different plants to identify the best approaches. Over the course of two years, the researchers tested the sequences using modified tobacco plants. That’s a common plant in science because its genome is exceptionally well-understood.
Those plants produced about 40 percent more biomass than non-modified plants. That indicates the more efficient photorespiration pathways save the plant considerable energy that can instead go toward growth. The next step is to incorporate the genes into food crops like soybean, cowpea, rice, and tomatoes.
It may take several years to integrate the revised photorespiration genes into food crops, which are more complicated than tobacco. The resulting plants would then have to be approved for human consumption by regulators — that’s no easy feat by itself, and there’s frequent anti-scientific opposition to genetically modified crops. RISE is supported by non-profits all over the world, including the Bill & Melinda Gates Foundation. Any seeds developed under RISE will be available royalty-free.