Heat is bad for plant health. Here’s how gene editing could help.

Some of the world’s most productive agricultural regions from India to the US Midwest have already broken temperature records this year, with potentially worrying implications for food supplies.

Hot days and nights can make drought conditions worse, and that’s not the only way rising temperatures can hurt crops. In extreme conditions, the molecular machinery inside plants can even shut down, leading to crop failures. That threat is expected to grow worse in the face of climate change.

Some plants, though, including major crops like corn and wheat, may face additional challenges from future warming, because heat impairs a major tool that they use to defend themselves against infections. When things warm up even slightly past normal levels, plants can become more vulnerable to pests. 

Biologists have started to figure out how this happens, and new research reveals routes to repair plants’ defenses without slowing growth. If it can be translated to real farms, altering crops in this way could help ensure that the food supply keeps up with population growth in a warming world.

Plants’ immune systems aren’t quite as complicated as humans’, but they do make chemicals in response to bacterial or fungal infections or insect attacks.

For many plants, an important immune pathway involves salicylic acid. The chemical has antibacterial properties, and it also acts as a signal to get other immune pathways going.

The problem is that in unusually hot conditions, this pathway basically shuts down. For crops that grow in normally cooler places like central Europe, for instance, a few days above 28 °C (84 °F) may be enough to hobble a plant’s defenses.

Researchers have known about this limitation for decades, but they’ve only recently started to understand exactly what’s going wrong and how they might step in to help. 

In a new paper, researchers identified one gene that seems to be the temperature-sensitive culprit and found a way to repair the plants’ immune system at higher temperatures.

Sheng Yang He, a plant biologist at Duke University and the Howard Hughes Medical Institute, and his team identified a gene called CBP60g that codes a protein controlling how other genes involved in the salicylic acid pathway are expressed.

Once the researchers found the gene, they were able to tweak the plants’ genome so they were forced to turn up salicylic acid production all the time, even at high temperatures. Eventually, the researchers also were able to make plants that made the defense chemicals only when they detected a pathogen, conserving energy and ensuring that the plants didn’t slow down their growth by making unnecessary defenses.

This research, like many fundamental plant studies, involved a plant called Arabidopsis, the lab rat of plant biology. Translating the work to other plants could be a challenge, says Cesar Cuevas-Velazquez, a plant biologist at the National Autonomous University of Mexico and one of the study’s reviewers.

Still, many relevant crop species are closely related to Arabidopsis, including broccoli and brussels sprouts. And because the salicylic acid pathway is present in many different kinds of plants, including major crops like wheat, corn, and potatoes, it’s possible the work could have an impact far beyond the lab. 

In a few follow-up experiments, the Duke group worked to repeat their results in rapeseed plants, a variety of which is used to make canola oil. The results were promising, although the work still needs to be tested in field trials, He says.  

One hold-up in getting the genetically modified crops into the field could be that the researchers used bacteria to deliver new DNA into the plant, meaning they would be considered GMOs (genetically modified organisms). But He says that future research could use gene-editing tools like CRISPR instead of introducing DNA from another organism, potentially avoiding some of the regulatory and consumer challenges associated with GMO foods.

Other experts are quick to point out that while research might be moving forward, we haven’t got plants totally figured out just yet.

“There are many more questions that are more fundamental,” says Jian Hua, a plant biologist at Cornell University. For example, she says, it’s not clear why this immune pathway shuts down at high temperatures in the first place.

Immune slowdowns at high temperatures could be an evolutionary quirk, but it’s also possible there is some benefit to switching off certain defenses as temperatures change, Hua points out. Some plants have other immune responses that actually ramp up when temperatures rise, and it’s not clear what the relative importance of these different pathways might be or how they might interact.

Rising temperatures brought on by climate change will affect plants in many ways beyond immunity, but if researchers could find new ways to help plants defend themselves, it could ultimately mean less pesticide use and a more resilient global food supply.

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