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Crops engineered to conserve water, resist drought

Single gene found in all plants controls stomata, which helps conserve water.

For the first time, scientists have improved how a crop uses water by 25% without compromising yield by altering the expression of one gene that is found in all plants, according to an announcement from the University of Illinois.

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 & Agriculture Research and the U.K. Department for International Development.

“This is a major breakthrough,” said RIPE director Stephen Long, the Ikenberry endowed chair of plant biology and crop sciences at the University of Illinois. “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.”

The international team increased the levels of a photosynthetic protein (PsbS) to conserve water by tricking plants into partially closing their stomata, the microscopic pores in the leaf that allow water to escape. Stomata are the gatekeepers to plants: When open, carbon dioxide enters the plant to fuel photosynthesis, but water is allowed to escape through the process of transpiration.

“These plants had more water than they needed, but that won’t always be the case,” said co-first author Katarzyna Glowacka, a postdoctoral researcher who led this study at the Carl R. Woese Institute for Genomic Biology (IGB). “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 team improved the plant’s water use efficiency — the ratio of carbon dioxide entering the plant to water escaping — by 25% without significantly sacrificing photosynthesis or yield in real-world field trials, the university said. The carbon dioxide concentration in the atmosphere has increased 25% in just 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, who is also a professor of crop sciences at Lancaster University in the U.K.

Four factors can trigger stomata to open and close: humidity, carbon dioxide levels in the plant, the quality of light and the quantity of light. This study is the first report of hacking stomatal responses to the quantity of light, the announcement said.

PsbS is a key part of a signaling pathway in the plant that relays information about the quantity of light. By increasing PsbS, the signal says there is not enough light energy for the plant to photosynthesize, which triggers the stomata to close, since carbon dioxide is not needed to fuel photosynthesis.

This research complements previous work -- published in Science -- that showed that increasing PsbS and two other proteins can improve photosynthesis and increase productivity by as much as 20%. Now, the team plans to combine the gains from these two studies to improve production and water use by balancing the expression of these three proteins.

For this study, the team tested their hypothesis using tobacco, a model crop that is easier to modify and faster to test than other crops. Next, they will apply their discoveries to improve the water use efficiency of food crops and test their efficacy in water-limited conditions.

“Making crop plants more water-use efficient is arguably the greatest challenge for current and future plant scientists,” said co-first author Johannes Kromdijk, a postdoctoral researcher at IGB. “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 paper, “Photosystem II Subunit S Overexpression Increases the Efficiency of Water Use in a Field-Grown Crop,” was published in Nature Communications.

RIPE is engineering crops to more efficiently turn the sun’s energy into food to sustainably increase worldwide food productivity. The project is led by the University of Illinois, in partnership with the University of Essex, Lancaster University, Australian National University, Chinese Academy of Sciences, Commonwealth Scientific & Industrial Research Organization, University of California-Berkeley, Louisiana State University and U.S. Department of Agriculture's Agricultural Research Service.

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