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Engineered plants conserve 25 percent more water by only partially opening their mouth-like stomata, allowing less water to escape through transpiration while carbon dioxide enters the plant to fuel photosynthesis. Credit: Jiayang Xie, Katarzyna Glowacka, Andrew D. B. Leakey

By altering a gene found in all plants, a group of scientists has found a way to improve how crops use water by 25 percent, without compromising the overall yield.

A team of scientists from the Realizing Increased Photosynthetic Efficiency (RIPE) project  has found that increasing the levels of a photosynthetic protein (PsbS) that is present in all plants prompted plants to partially close their stomata—the microscopic pores in the leaf that allow water to escape.

“This is a major breakthrough,” RIPE Director Stephen Long, the Ikenberry Endowed Chair of Plant Biology and Crop Sciences at the University of Illinois, said in a statement. “Crop yields have steadily improved over the past 60 years, but the amount of water required to produce one ton of grain remains unchanged—which led most to assume that this factor could not change.

“Proving that our theory works in practice should open the door to much more research and development to achieve this all-important goal for the future.”

When the stomata is open, carbon dioxide enters the plant to fuel photosynthesis. However, water escapes through the process of transpiration.

“These plants had more water than they needed, but that won’t always be the case,” co-first author Katarzyna Glowacka, a postdoctoral researcher who led this research at the Carl R. Woese Institute for Genomic Biology (IGB), said in a statement. “When water is limited, these modified plants will grow faster and yield more—they will pay less of a penalty than their non-modified counterparts.”

The stomata opens and closes due to humidity, carbon dioxide levels in the plant, the quality of light or the quantity of light.

PsbS relays information about the quantity of light, so by increasing PsbS, the signaling pathway indicates that there is not enough light energy for the plant to photosynthesize, triggering the stomata to close.

The carbon dioxide concentration in the atmosphere has also increased by 25 percent in the past 70 years, allowing the plant to amass enough carbon dioxide without fully opening its stomata.

“Evolution has not kept pace with this rapid change, so scientists have given it a helping hand,” said Long.

The team previously discovered that increasing PsbS and two other proteins could improve photosynthesis and increase productivity by as much as 20 percent.

The researchers now plan to combine the gains from the two studies to improve the production and water-use by balancing the expression of all three proteins.

Although agriculture already accounts for about 90 percent of global freshwater, production needs to dramatically increase to feed and fuel the growing global population.

“Making crop plants more water-use efficient is arguably the greatest challenge for current and future plant scientists,” co-first author Johannes Kromdijk, a postdoctoral researcher at the IGB, said in a statement. “Our results show that increased PsbS expression allows crop plants to be more conservative with water use, which we think will help to better distribute available water resources over the duration of the growing season and keep the crop more productive during dry spells.”

The research is part of the international research project Realizing Increased Photosynthetic Efficiency (RIPE) that is supported by the Bill & Melinda Gates Foundation, the Foundation for Food and Agriculture Research, and the U.K. Department for International Development.

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