Scientists tinker with plant receptors, produce drought-resistant crops

By tweaking a plant's ability to regulate water, scientists could make plants that survive longer in dry conditions.

Evidence of increasing levels of drought in some regions puts at risk the ability to successfully grow crops there. But what if plants could better keep their water supply from shrinking?

Scientists have tweaked plants’ chemical receptors that regulate water use so that they respond to a commonly used fungicide and, as a result, conserve water. The findings, which were published Wednesday in the journal Nature, may allow for crops to become more resistant to drought and heat stress.

Plants geneticists have known for some time that plants contain receptors that signal whether to conserve water or use it, but for years scientists were unable to locate these receptors. In 2009, a number of research teams pinpointed the receptors’ location and began investigating ways to manipulate them to improve crop production. One of those teams was led by University of California, Riverside, plant biologist Sean Cutler, and the group’s most recent work changes the way plant receptors work.

Normally, when a plant is not receiving sufficient water, it begins to increase production of abscisic acid (ABA). The chemical acts as the catalyst for abscisic acid receptors to regulate water use. And those receptors, which are part of a larger signaling network, do that by controlling the aperture of the plant’s stomata, or pores. The less open the pores are, the less water escapes.

“Plants face this intrinsic trade-off between growing and consuming water. There’s a need for the plant to coordinate its growth with how much water is available,” Cutler told the Monitor. “And plants use a small molecule hormone called abscisic acid to sort of make that signaling occur.”

So Cutler and his colleagues developed a new version of the ABA receptor that, when exposed to a commonly used fungicide called mandipropamid, responded in the same way it typically does to abscisic acid. The mandipropamid signaled the guard cells, which surround the stomata, to close the pores in order to keep water vapor in, rather than allowing it to escape in exchange for carbon dioxide.

Mandipropamid was a win-win for the research team: the chemical provided the research team with successful response by the altered receptor, and it had already passed the regulatory hurdles for use on farms. 

“We wanted to take a molecule that was already used in agriculture so it had already gone through all those hurdles,” says Cutler. “We knew there was no intrinsic barrier to it being used in the field.” 

They tested the receptors in Arabidopsis, an edible plant in the mustard family that is widely used in genetic testing, but they also saw the receptors work in tomato plants, a crop grown on almost every continent.

Repurposing the agrochemical in this way is providing one solution to a serious global issue: food security. Though substantially more crops will be needed in the near future to support the world's population, large quantities of potential food are being lost to drought each year, says Cutler. And although the findings of Cutler and his colleagues don’t yet address instances of extreme drought, common cases where farmers lose, say, one third of their crop yields could be resolved by the technique. 

“All crops – all plants – need water to grow,” says Cutler. “We’re not going to turn tomatoes or corn into cacti, but what we’re trying to do is recover as much of the yield that gets lost to moderate drought.”

Altering the ABA receptor, however, does mean these plants better equipped to handle drought would be genetically modified ones. Some plant scientists claim that, by introducing foreign genes into plants, consequences like harmful mutations or the introduction of new pathogens could arise. Cutler argues that the new ABA receptor isn’t entirely foreign: they’re placing a plant gene back into a plant.

“We’re tinkering with the plant gene. We’re not putting back in things that were never ever there,” says Cutler.

Now the research team will spend more time investigating tomato plants and other widely-used crops to see how well they perform with the new receptors. They also hope to make the reprogrammed receptors as targeted as possible, so as to help the plant conserve water while avoiding any undesirable effects, like a plant’s leaves drying out and turning yellow.

“It will, we believe, allow us to be very precise in the physiological effects that we get and, we hope, minimize whatever negative effects there could be from activating it in other tissues or cell types besides those guard cells,” Cutler says.