Scientists correct failure in photosynthesis to make plants grow more than 40%


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All that oxygen you like to breathe does not just magically appear in the atmosphere. Earth is habitable because plants around the globe pump oxygen as a byproduct of photosynthesis, and some of them become palatable foods in addition. However, photosynthesis is not perfect, despite many evolutionary refinements. Scientists at the University of Illinois worked to correct a flaw in photosynthesis, and that could improve yields by as much as 40 percent.

At the center of the new research is a process in plants called photorespiration, which is not part of photosynthesis, as it is a consequence of this. Like many biological processes, photosynthesis does not work correctly 100% of the time. In fact, one of the main reactions of photosynthesis is only about 75% effective. Change comes in the process that plants undertake because of this inefficiency.

In photosynthesis, plants absorb water and carbon dioxide and process it to create sugars (food) and oxygen. Plants do not need oxygen and are expelled. Fortunately, we 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 binds a carbon dioxide molecule to ribulose-1,5-bisphosphate (RuBP). Over time, the Earth's atmosphere has become more oxygenated and that means that RuBisCO has to deal with more oxygen molecules mixed with carbon dioxide. About a quarter of the time, RuBisCO mistakenly picks up an oxygen molecule and this has consequences inside a factory.

Scientists Don Ort (right), Paul South (center) and Amanda Cavanagh (left) study how well their modified plants to avoid photorespiration develop alongside unmodified plants in real world conditions.

When RuBisCO is spoiled, plants are left with toxic byproducts such as glycollate and ammonia. It takes energy to process these compounds (through photorespiration), which is added to the loss of energy by the inefficiency of photosynthesis. The study authors note that rice, wheat and soybeans suffer from this failure, and RuBisCO is even less accurate as temperatures rise. This means that food supplies may decline as global warming becomes more severe.

The correction is part of a program called Realizing Increased Photosynthetic Efficiency (RIPE), and features the introduction of new genes that improve growth. Typically, photorespiration takes a tortuous and complex route through three different cell organelles. It consumes ATP (the energy currency of cells) that should be making the plant bigger and stronger. RIPE focuses on making photorespiration faster and more energy efficient.

The team developed three alternative pathways using new genetic sequences. They optimized these paths in 1,700 different plants to identify the best approaches. Over the course of two years, the researchers tested the sequences using modified tobacco plants. This is a common plant in science because its genome is exceptionally well understood.

These plants produced about 40% more biomass than unmodified plants. This indicates that the most efficient photoresist pathways save considerable energy from the plant, which may instead be growth-driven. The next step is to incorporate genes into food crops, such as soybeans, cowpea, rice and tomato.

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 – this is not an easy task by itself, and there is frequent anti-scientific opposition to genetically modified crops. RISE is supported by non-profit organizations around the world, including the Bill & Melinda Gates Foundation. Any seeds developed under RISE will be available without royalty.

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