Photorespiratory shortcut boosts crop growth 40%

The process with which plants convert sunlight into energy is called photosynthesis. According to scientists, most crops on the planet are plagued by a photosynthetic glitch. In order to deal with that glitch, crops evolved a process called photorespiration. However, photorespiration is energy-expensive and drastically suppresses their yield potential.

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Scientists Don Ort (left), Paul South (center) and Amanda Cavanagh (right) study how well their plants modified to bypass photorespiration perform beside unmodified plants in real-world conditions. They found that plants engineered with a synthetic shortcut are about 40 percent more productive. Photo: Claire Benjamin/RIPE Project

Photorespiratory shortcut

Science Daily reports that scientists have developed what they call a photorespiratory shortcut, as researchers from the University of Illinois and U.S. Department of Agriculture Agricultural Research Service recently reported in the journal Science. According to them, crops engineered with this photorespiratory shortcut are 40 percent more productive in real-world agronomic conditions.

Up to 200 million additional people could be fed with the calories lost to photorespiration in the Midwestern U.S. each year

“Up to 200 million additional people could be fed with the calories lost to photorespiration in the Midwestern U.S. each year,” said principal investigator Donald Ort, the Robert Emerson Professor of Plant Science and Crop Sciences at Illinois’ Carl R. Woese Institute for Genomic Biology. According to Ort, 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 – driven by population growth and more affluent high-calorie diets.

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Four unmodified plants (left) grow beside four plants (right) engineered with alternate routes to bypass photorespiration – an energy-expensive process that costs yield potential. The modified plants are able to reinvest their energy and resources to boost productivity by 40 percent. – Photo: Claire Benjamin/RIPE Project

Rubisco

So, how does it work? The key is the enzyme Rubisco, used in photosynthesis together with sunlight energy to turn carbon dioxide and water into sugars that fuel plant growth and yield. As it turns out, Rubisco has been too succesful, creating an oxygen-rich atmosphere. Since Rubisco is unable to reliably distinguish between the 2 molecules, it grabs oxygen instead of carbon dioxide about 20 percent of the time. This in turn results in a plant-toxic compound that must be recycled through the process of photorespiration.

Photorespiration is anti-photosynthesis

Basically, photorespiration is anti-photosynthesis, said lead author Paul South, a research molecular biologist with the Agricultural Research Service, who works on the RIPE project at Illinois. “It costs the plant precious energy and resources that it could have invested in photosynthesis to produce more growth and yield.”

3 alternate routes

Under normal conditions photorespiration takes a complicated route through 3 compartments in the plant cell. Scientists engineered alternate pathways to reroute the process. The team engineered 3 alternate routes to replace the circuitous native pathway. To optimize the new routes, they designed genetic constructs using different sets of promoters and genes, creating a suite of unique roadmaps.These drastically shorten the trip which, they claim, saves enough resources to boost plant growth by 40 percent.

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They stress tested these roadmaps in 1,700 plants to winnow down the top performers.This is the first time that an engineered photorespiration fix has been tested in real-world agronomic conditions. “These photorespiratory shortcuts are a feat of plant engineering that prove a unique means to greatly increase the efficiency of photosynthesis,” said RIPE Director Stephen Long, the Ikenberry Endowed University Chair of Crop Sciences and Plant Biology at Illinois.

40 percent more biomass

Over 2 years of replicated field studies, the researchers found that these engineered plants developed faster, grew taller, and produced about 40 percent more biomass, most of which was found in 50-percent-larger stems.

The hypotheses was tested in tobacco, because tobacco is an ideal model plant for crop research. It is easier to modify and test than food crops, yet unlike alternative plant models, it develops a leaf canopy and can be tested in the field. Now, the team is translating these findings to boost the yield of soybean, cowpea, rice, potato, tomato, and eggplant.

Our goal is to build better plants that can take the heat today and in the future, to help equip farmers with the technology they need to feed the world

“Rubisco has even more trouble picking out carbon dioxide from oxygen as it gets hotter, causing more photorespiration,” said co-author Amanda Cavanagh, an Illinois postdoctoral researcher working on the RIPE project. “Our goal is to build better plants that can take the heat today and in the future, to help equip farmers with the technology they need to feed the world.”

That won’t happen tomorrow. Acccording to the researchers, it will likely take more than a decade for this technology to be translated into food crops and achieve regulatory approval. Still, RIPE and its sponsors are committed to ensuring that smallholder farmers, particularly in Sub-Saharan Africa and Southeast Asia, will have royalty-free access to all of the project’s breakthroughs.

Also read: Optimizing photosynthesis to double crop production