Tomato plants use their roots to ration water during drought

In a world where the climate is increasingly unpredictable, understanding how plants adapt and survive becomes crucial. 

A new study from UC Davis sheds light on how tomato plants use their roots to ration water during drought conditions, marking a significant advancement in agricultural research and potential crop resilience strategies.

Focus of the study 

Central to this discovery is a substance called suberin, a water-repellent polymer. Suberin plays a critical role in how plants manage water resources under stress. 

Typically, during a drought, plant roots produce suberin to block water from flowing upwards towards the leaves. This mechanism is vital since water reaching the leaves would quickly evaporate. Comparing this to an open tap, without suberin, plants would suffer significant water loss.

Unique adaptation

While suberin is not new to botanists, its production in tomato plants presents a unique case. In most plants, suberin is produced by endodermal cells within the root’s inner vessels. 

However, in tomato plants, researchers found that suberin is produced in exodermal cells, situated just beneath the root’s skin. This distinction was previously not well understood.

The role of exodermal suberin

The research illuminates the role of exodermal suberin in tomato plants. Led by Siobhan Brady, a professor in the UC Davis Department of Plant Biology and Genome Center, and postdoctoral scholar Alex Cantó-Pastor, the team demonstrated that exodermal suberin serves a similar function to endodermal suberin. 

The study revealed that without this protective layer, tomato plants show decreased resilience to water stress.

“This adds exodermal suberin to our toolbox of ways to help plants survive for longer and cope with drought,” said Professor Brady. 

“It’s almost like a jigsaw puzzle – if you can figure out which cells have modifications that protect the plant during difficult environmental conditions, you can start to ask questions like, if you build those defenses up one upon the other, does it make the plant stronger?”

How the research was conducted 

The team began by identifying active genes in the root exodermal cells of tomato plants. Following this, gene editing was used to create mutant strains which lacked certain genes believed to be involved in suberin production. This led to the identification of seven essential genes for suberin deposition.

Focusing on two genes, SIASFT and SlMYB92, the researchers conducted drought experiments. These genes, one an enzyme and the other a transcription factor, are critical in suberin production. 

Key insights

Mutant plants, deficient in the genes needed for suberin production, exhibited increased wilting and stress under drought conditions compared to normal, well-watered plants.

“In both of those cases where you have mutations in those genes, the plants are more stressed and they’re not able to respond to drought conditions,” said Brady.

Future directions 

Having established suberin’s effectiveness in a controlled environment, the next step involves field testing. Professor Brady and her team aim to apply this knowledge to improve drought tolerance in tomatoes, a move that could revolutionize agricultural practices.

“We’ve been working on taking this finding and putting it into the field to try and make tomatoes more drought tolerant,” said Brady.

The research was supported by the National Science Foundation and the Howard Hughes Medical Institute.

The study is published in the journal Nature Plants. 

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