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Engineering plants with deeper roots could be a huge climate boon. Scientists just made a big find.

DAILY SCIENCE

Engineering plants with deeper roots could be a huge climate boon. Scientists just made a big find.

By tweaking a key plant hormone, researchers believe we can grow crops that burrow deeper into the soil, lock up carbon, clean up pollution, and more.
February 23, 2024

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A host of agricultural challenges—crops’ vulnerability to drought, massive nitrogen pollution and greenhouse gas emissions—share one elegant solution: getting plants to grow longer, deeper roots.

It may sound odd, but in fact this feat of genetic engineering has occupied scientists for years. Now, writing in Cell Reports, one research team thinks they have hit on an especially promising way to achieve this goal: by tweaking the behavior of a particular plant hormone, they believe we can grow plants that burrow deeper into the soil.

Such deep-reaching roots have real potential for crop health and the environment. Not only do deep-rooted plants have a better chance of reaching water in times of drought, they also capture more of the excess nitrogen that filters into the soil of fertilized farmland, helping tackle nutrient pollution. What’s more, long roots deposit carbon into deeper soil layers, “where it stays for longer and can be kept out of the atmosphere,” explains Wolfgang Busch, executive director of the Harnessing Plants Initiative at the Salk Institute, whose lab led the new work. That’s thanks in part to suberin, an abundant tissue in plant roots that locks away carbon and, conveniently, is slow to decompose.

With this huge potential in mind, Busch and team set out to discover new ways to shape the root architecture of plants. Building on their previous work, which explored the role of the hormone auxin in moderating root growth, this study pivoted to look at another hormone, ethylene, and its potential role in root architecture. Ethylene is well-studied and well-known, but this is the first research to link it to the precise angles at which roots grow.

So, why ethylene? The clue to this came from a molecule called mebendazole (MBZ), which triggers a cascade effect that ultimately shapes the ethylene pathway and root growth in plants. The researchers made this discovery after they went on a hunt for ingredients that could influence the root architecture of their test plant, thale cress. That involved a genetic screen of the cress, which identified a wide array of chemicals that may influence root growth, one of which was MBZ.

 

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The researchers found that when the test plants received a treatment of mebendazole, their roots grew more horizontally, and shallower in the soil—the exact opposite of what the team wanted, in fact. But, this discovery shone a light on where they could start looking, if they wanted to change that pattern of growth. 

Through this, they found out that MBZ deactivates an enzyme, whose activity would usually suppress parts of the ethylene pathway, in a way that results in longer roots with deeper growth. But by suppressing this enzyme, mebendazole indirectly then activates the ethylene pathway, leading to the development of shallow, horizontally-reaching roots. 

With this discovery, “MBZ has unlocked the ethylene pathway as a target for engineering deeper roots,” Busch explains. “This told us that we might get steeper roots when ethylene signaling is abolished. In fact, we found that in plants in which ethylene signaling doesn’t work…we get steeper roots.”

The discovery that the ethylene pathway curates root growth is particularly exciting to Busch and team, because this pathway is common—or ‘highly conserved’—across many plant species. That means there could be significant potential to engineer root growth in different types of plants, including crops. 

This will require some surgical precision, however. Ethylene is an important feature in several elements of plant growth, not just the direction in which roots grow. For instance, it’s a key ingredient in fruit ripening. So, highly-targeted engineering is the researchers’ next goal.

“Right now we are very busy testing out many ethylene signaling engineering concepts in our model species [thale cress]. These concepts are based on very precise manipulations of the ethylene pathway in a small number of cells in roots, so we can change root steepness but not any other plant properties.”

Once they’ve achieved this in greenhouse plants, they’ll be able to move their experiment into the field: Busch estimates that they could be ready to do that in a couple of years. Before too long, that might lead to crops that are both climate-resilient, and able to help mitigate climate change. “Deep roots are…a winning solution for the environment and crop health,” says Busch.

He et. al. “Identification of mebendazole as an ethylene signaling activator reveals a role of ethylene signaling in the regulation of lateral root angles.” Cell Reports. 2024.

Image: Wikimedia Commons

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