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Pathways to stimulate crop growth through bypassing photorespiration
Plants convert sunlight into energy through photosynthesis. However, most crops on the planet are plagued by a photosynthetic glitch, and to deal with it, they have evolved an energy-expensive process called photorespiration that drastically suppresses their yield potential. Today, researchers from the University of Illinois/USA and the US Department of Agriculture report in the journal Science that crops engineered with a photorespiratory shortcut are 40 per cent more productive in real-world agronomic conditions.
The study is part of “Realizing Increased Photosynthetic Efficiency” (RIPE), an international research project that is engineering crops to photosynthesise more efficiently to sustainably increase world-wide food productivity with support from the Bill & Melinda Gates Foundation, the Foundation for Food and Agriculture Research (FFAR) and the UK Government’s Department for International Development (DFID).
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 per cent of the time, resulting in a plant-toxic compound that must be recycled through the process of photorespiration.
“Photorespiration is anti-photosynthesis,” said the RIPE study’s lead author Paul South, a research molecular biologist with the Agricultural Research Service who works on the 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. RIPE scientists engineered alternate pathways to reroute the process, drastically shortening the trip and saving enough resources to boost plant growth by 40 per cent. This is the first time that an engineered photorespiration fix has been tested in real-world agronomic conditions.
Producing 40 per cent more biomass
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, essentially creating a suite of unique roadmaps. 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 per cent more biomass, most of which was found in 50-per-cent-larger stems.
The team tested their hypotheses in tobacco, which is 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 are translating their findings to boost the yield of soybean, cowpea, rice, potato, tomato and eggplant.
While it will likely take more than a decade for this technology to be translated into food crops and achieve regulatory approval, 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.
Paul South et al. (2019): “Synthetic glycolate metabolism pathways stimulate crop growth and productivity in the field”
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