8th January 2019

Genetic "shortcut" boosts plant growth by 40%

Scientists report the engineering of crops with a photorespiratory "shortcut" to boost plant growth by 40% in real-world agronomic conditions.



Credit: Paul F. South, et al. / Science

Plants convert sunlight into energy through photosynthesis; however, most crops on the planet are plagued by a photosynthetic glitch, and to deal with it, evolved an energy-expensive process called photorespiration, which drastically suppresses their yield potential. Researchers from the University of Illinois and U.S. Department of Agriculture Agricultural Research Service report in the journal Science that crops engineered with a photorespiratory "shortcut" are 40% more productive in real-world agronomic conditions.

"We could feed up to 200 million additional people with the calories lost to photorespiration in the Midwestern U.S. each year," said Donald Ort, a professor of plant biology at the University of Illinois at Urbana-Champaign. "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."

This landmark study is part of Realising Increased Photosynthetic Efficiency (RIPE), an international research project that is engineering crops to photosynthesise more efficiently to sustainably increase worldwide food productivity. It has support from the Bill & Melinda Gates Foundation, the Foundation for Food and Agriculture Research (FFAR), and the U.K. Government's Department for International Development (DFID).



Scientists Don Ort (left), Paul South (centre) and Amanda Cavanagh (right). Credit: Claire Benjamin/RIPE Project

Photosynthesis uses the enzyme Rubisco – the planet's most abundant protein – and sunlight energy to turn carbon dioxide and water into sugars that fuel plant growth and yield. Over millennia, Rubisco has become a victim of its own success, creating an oxygen-rich atmosphere. Unable to reliably distinguish between the two molecules, Rubisco grabs oxygen instead of carbon dioxide about 20% of the time, resulting in a plant-toxic compound that must be recycled through the process of photorespiration.

"Photorespiration is anti-photosynthesis," said lead author Paul South, a 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."

Photorespiration normally takes a complicated "route" through three compartments in the plant cell. Scientists engineered alternate pathways to reroute it, drastically shortening the trip and saving enough resources to boost plant growth by 40%. This is the first time that an engineered photorespiration fix has been tested in real-world agronomic conditions.

"Much like the Panama Canal was a feat of engineering that increased the efficiency of trade, 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 team engineered three alternate routes to replace the circuitous native pathway. To optimise the new routes, they designed genetic constructs using different sets of promoters and genes. They stress-tested these roadmaps in 1,700 plants to winnow down the top performers. Over two years of replicated field studies, they found that these engineered plants developed faster, grew taller, and produced about 40% more biomass, most of which was found in 50% larger stems.

The team tested their hypotheses in tobacco: an ideal model plant for crop research, because 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.

"Rubisco has even more trouble picking out carbon dioxide from oxygen as it gets hotter, causing more photorespiration," said Amanda Cavanagh, an Illinois postdoctoral researcher. "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."

Although it will likely take more than a decade for this technology to be translated into food crops with regulatory approval, RIPE and its sponsors are committed to ensuring that smallholder farmers, particularly in Africa and Southeast Asia, will have royalty-free access to all of the project's breakthroughs.

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