STANFORD, Calif. – Plants depend on water for survival, so it’s no surprise that some plants can direct and grow their roots toward water. Researchers call this mechanism “hydropatterning,” or how plant roots branch toward sources of water in the soil and avoid dry spaces.

José Dinneny, a professor of biology at Stanford University’s School of Humanities and Sciences, and his team are interested in understanding root systems and how roots contribute to a plant’s ability to tolerate stresses such as drought. While investigating root systems, the group observed that roots could perceive differences in contact with water or air. When plants were grown along a wet surface, they branched toward that surface and did not branch in areas where roots were exposed to air.

While roots can’t “see” per se, they do produce hormones that help them perceive differences in their environment. Dinneny and his team conducted genetic analyses that found two plant hormones, auxin and ethylene, contribute to hydropatterning. Auxin, a plant hormone that controls cell growth, division, and differentiation, helps to signal root branches toward water. Ethylene, a plant hormone that regulates growth and senescence, suppresses root branching when the root is exposed to air.

Beyond understanding the how of hydropatterning, Dinneny and his team were also interested in understanding whether these responses would be important for crop plants.

“We investigated whether there was diversity in this hydropatterning response in modern inbreds that are used for maize breeding. What we saw is that there is actually a significant amount (of diversity), and it wasn’t uniformly distributed across these breeding populations,” Dinneny said. “There seems to have been differential selective pressures that breeders have placed on these different populations.”

The results of the research indicated that corn varieties grown in tropical or subtropical areas displayed strong hydropatterning behaviors. Other breeding lines, like those present in North America, display weaker hydropatterning behaviors.

“One hypothesis that I think is worth exploring is that the high input, high fertility fields that breeders were using to generate these inbreds may have led to lower selective pressure on these inbreds as a whole and may have led to the degradation of this environmental response that helps plants find water,” Dinneny said of the diversity of responses in corn varieties.

Additionally, the team found that plants that are better at sensing where water is also make deeper root systems. Dinneny said a hypothesis for this mechanism could be that if the plant doesn’t waste energy growing root branches into places where it doesn’t find any water and nutrients, then it has more energy to grow deeper down where water is more likely.

More research is needed to understand the variations in hydropatterning between plants. Dinneny and his team are interested in exploring the exact location where the different inbreds are utilized in breeding programs to see if inbreds with weaker hydropatterning are grown in areas that are either less susceptible to drought or in which the inbreds are being primarily used as a male in crossbreeding.

“As we try to move agriculture to more sustainable practices, developing breeding lines that are better able to take advantage of the limited resources that they have in the environment may be useful. What these data indicate to us is that through modern breeding of maize inbreds, there may have been a lack of selective pressure for sustainability traits, such as hydropatterning,” Dinneny said. “I think phenotyping or characterizing hydropatterning, especially in the modern elite varieties that companies are using to generate their maize material, would be very exciting. I think there could be even greater impact outside of the U.S. in agricultural situations where limited resources have a bigger impact on agricultural productivity, such as in Africa.”

Dinneny added that hydropatterning has been identified in other plants besides maize. The trait was originally discovered in rice and the trait exists in members of the Brassicaceae family, which includes mustards and cabbages.

“I think it’s likely that most flowering plants have hydropatterning in their root systems, and the next step in any crop of interest would be to see if there’s variation for hydropatterning and whether there might be an advantage to select for stronger hydropatterning material,” he said.

Moving forward, the team is interested in understanding the genes and molecular pathways by which plants can perceive moisture in the environment. Characterizing the genes responsible for hydropatterning would allow researchers to create biotechnological solutions to manipulate the activity of the genes in crops of interest, tuning the plants to have stronger or weaker hydropatterning depending on the agricultural situation.