How Tomato Plants Use Their Roots to Ration Water During Drought

Plants must be flexible to survive environmental changes, and the methods of adaptation they deploy must often be as changeable as climate change and the conditions to which they adapt. To cope with drought, plant roots produce a water-repellent polymer called suberin that prevents water from flowing up to the leaves, where it would quickly evaporate. Without suberin, the resulting loss of water would be like leaving the faucet running.

In some plants, suberin is produced by the endodermal cells that line the vessels inside the roots. But in others, like tomatoes, suberin is produced in exodermal cells just under the root skin.

The role of exodermal suberin has long been unknown, but a new study by researchers at the University of California, Davis, published January 2 in Natural plants shows that it performs the same function as endodermal suberin and that without it, tomato plants are less able to cope with water stress. This information could help scientists design drought-resistant crops.

“This adds exodermal suberin to our toolbox to help plants survive longer and cope with drought,” said Siobhan Brady, a professor in the Department of Plant Biology and Genome Center at UC Davis, and lead author of the article. “It’s almost like a puzzle: If you can determine which cells have modifications that protect the plant in harsh environmental conditions, you can start to ask questions like: If you build these defenses on top of each other, Does this make the plant more resilient? stronger?”

In the new study, postdoctoral researcher Alex Cantó-Pastor worked with Brady and an international team of collaborators to uncover the role of exodermal suberin and map the genetic pathways that regulate its production.

Combining new and classic methods

“It’s really the fusion of classical and cutting-edge methodologies that allows us to look at both the process that’s happening in an individual cell and what we see throughout the plant,” Brady said. . “So going from super small to really, really big.”

Brady, Cantó-Pastor and their colleagues began by identifying all the genes actively used by root exodermal cells. Next, they performed gene editing to create mutant strains of tomato plants lacking functional versions of several genes they suspected were involved in suberin production. They discovered seven genes necessary for suberin deposition.

Next, the researchers tested the role of exodermal suberin in drought tolerance by exposing certain mutant tomato plants to a ten-day drought. For these experiments, the researchers focused on two genes: SIASFT, an enzyme involved in suberin production, and SlMYB92, a transcription factor that controls the expression of other genes involved in suberin production.

The experiments confirmed that both genes are necessary for suberin production and that without them, tomato plants are less able to cope with water stress. The mutant plants grew as well as normal plants when watered well, but became much more wilted after ten days without water.

“In both cases where there are mutations in these genes, the plants are more stressed and are not able to respond to drought conditions,” Brady said.

Having demonstrated the value of suberin in the greenhouse, the researchers now plan to test the drought resistance potential of suberin in the field.

“We worked on this discovery and applied it in the field to try to make tomatoes more drought tolerant,” Brady said.