Figure: Scientists plant tobacco seedlings by hand to test alternate photorespiratory pathways in real-world field conditions. They found that these synthetic shortcuts boost productivity by 40 percent, and will now apply this breakthrough to boost the yield of food crops.

Photosynthesis uses the enzyme Rubisco and sunlight to turn carbon dioxide and water into sugars essential for plant growth and yield. Over millennia, Rubisco has created an oxygen-rich atmosphere, using oxygen instead of carbon dioxide about 20 percent 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 research molecular biologist with the Agricultural Research Service, who works on the project Realizing Increased Photosynthetic Efficiency (RIPE) in 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 the process, drastically shortening the trip and saving enough resources to boost plant growth by 40 percent. This is the first time that an engineered photorespiration fix has been tested in real-world agronomic conditions.

The researchers engineered three alternate routes to replace the circuitous native pathway. To optimize the new routes, they designed genetic constructs with different sets of promoters and genes, essentially creating a suite of unique roadmaps. They stress tested these roadmaps in 1,700 plants to identify the top performers. Over two 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 team tested their hypotheses in tobacco and is now translating their findings to boost the yield of soybean, cowpea, rice, potato, tomato, and eggplant.

For more details, read the news article from the University of Illinois.