Scientists led by the University of Illinois have discovered that a simple genetic tweak, which alters the expression of a single gene that is found in all plants, can improve how a crop uses water by 25% without compromising yield.

When the microscopic pores in leaves, called stomata, are open, carbon dioxide enters the plant to fuel photosynthesis but water is allowed to escape through the process of transpiration. Because the carbon dioxide concentration in the atmosphere has increased by 25% in the past 70 years, plants can now get enough carbon dioxide without fully opening their stomata – but natural evolution has not kept up with this rapid change.

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.

The research team increased the levels of a photosynthetic protein called Photosystem II Subunit S (PsbS) which is a key part of a signaling pathway in the plant that relays information about the quantity of light. Increasing PsbS signals 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.

The increased level of PsbS, by tricking plants into partially closing their stomata, improves 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.

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. Now they will apply their discoveries to improve the water-use-efficiency of food crops and test their efficacy in water-limited conditions.

The researchers believe that their discovery will help to better distribute available water resources over the duration of the growing season and keep crops more productive during dry spells.