A genetic hack to make crops 25% less thirsty

By altering the behaviour of a single gene, scientists can engineer a crops to need 25% less water than normal plants. This revolutionary new discovery, published in Nature Communications, could help us grow crops that save vast amounts of water–an already threatened global resource–and boost global food security at the same time, writes the study’s team of international researchers.

The researchers found that by increasing expression in a gene called Photosystem II Subunit S (PsbS), they could trick plants into partially closing their stomata and keeping water locked in. These microscopic holes usually expand to let in carbon dioxide for photosynthesis–but also release water during that process. It was assumed, therefore, that tightening the stomata to limit water loss would result in a trade-off–limiting CO2 access and undermining photosynthesis.

However, the researchers discovered that because atmospheric levels of CO2 are now so high, plants with the modified, tighter stomata could actually go on photosynthesising at the same rates–and still save a quarter of their water reserves. “Evolution has not kept pace with this rapid change, so scientists have given it a helping hand,” says study author Stephen Long.

Agriculture already slurps up an astounding 90% of Earth’s freshwater. And, as the global climate grows hotter and drier–doubled up with the pressure to increase food production to feed more people–that resource will dwindle. So there’s little doubt that we need to develop less water-intensive ways to grow food; the researchers think their findings float a solution.

They made their discovery by examining PsbS in tobacco plants. This gene is involved in a signalling pathway which tells the plant how much light it’s bathed in, so that when there’s a lot, the plant ‘knows’ to take advantage by amping up photosynthesis. But in plants whose PsbS genes expressed more, the researchers discovered that this signal was dimmed. That effectively told the stomata that there wasn’t enough light for them to bother photosynthesising, making them close up–and retain more of the plant’s moisture.

Under both controlled and field conditions, the researchers found that the tobacco plants with higher levels of gene expression didn’t significantly affect their growth or yields. That allowed them to achieve the same rates of photosynthesis, but with a quarter less moisture.

Because the PsbS gene is found widely in plants, not just tobacco, the findings are relevant to many other crops as well. Next, the study researchers say they’ll be focusing on how this water-saving dynamic plays out in water-stressed food crops.

If it works in staple species–such as wheat and rice–it might not only increase the quantity we can sustainably farm, but could also significantly reduce the impact of our food. “Making crop plants more water-use efficient is arguably the greatest challenge for current and future plant scientists,” asserts study co-author Johannes Kromdijk.

Source: Glowacka et. al. “Photosystem II Subunit S overexpression increases the efficiency of water use in a field-grown crop.” Nature Communications. 2018.
Image: Pxhere

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