Crops Engineered to Conserve Water Without Drop in Yield

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. (Jiayang Xie, Katarzyna Glowacka, Andrew D.B. Leakey)

(CN) – A new technique enables crops to use water 25 percent more efficiently without compromising yield, according to a study published Tuesday in the journal Nature Communications.

While agriculture already requires 90 percent of global freshwater, more will be needed as production increases to feed the growing population. Additional water will also be needed to offset the impact of climate change on crops.

In the report, researchers shows how altering the expression of a single gene found in all plants can make at least one crop – tobacco – use water more efficiently. Tobacco was used because it is easier to modify and quicker to test than other crops.

“This is a major breakthrough,” said co-author Stephen Long, director of Realizing Increased Photosynthetic Efficiency (RIPE) at the University of Illinois at Urbana-Champaign.

The new study is part of RIPE, an international research project funded by the Bill & Melinda Gates Foundation, the Foundation for Food and Agriculture Research, and the U.K. Department for International Development.

“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,” Long said.

“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 researchers raised the levels of a photosynthetic protein (PsbS) to save water by tricking plants into partially shutting their stomata – microscopic pores in leaves that let water escape.

Stomata serve as the gatekeepers to plants. When open, carbon dioxide enters the plant to stimulate photosynthesis, but water escapes 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 the study at the Carl R. Woese Institute for Genomic Biology at the University of Illinois.

“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.”

In real-world field trials, the researchers improved the tobacco plants’ water-use efficiency – the ratio of CO2 entering the plant to water escape – by 25 percent without significantly compromising photosynthesis or yield.

The concentration of CO2 in our atmosphere has increased by 25 percent in just the last 70 years, which allows the plant to accrue enough CO2 without completely opening its stomata.

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

Four factors can cause stomata to open and close: CO2 levels in the plant, humidity and the quality and quantity of light. This research is the first report of tricking stomatal responses to light quantity.

PsbS is a key component of a signaling pathway in the plant that communicates information about the quantity of light. By boosting PsbS, the signal indicates there is not enough light energy for the plant to photosynthesize, which leads the stomata to close as CO2 is not needed to enable photosynthesis.

The findings complement previous work that demonstrated increasing PsbS and two other proteins can enhance photosynthesis and heighten productivity by as much as 20 percent.

Researchers now plan to combine the findings from these studies to improve production and water use by balancing the expression of the three proteins. They will apply their results to others 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 the 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.”

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