Gene discovery could help roots grow deeper

A research team led by the Salk Institute for Biological Sciences has discovered a gene that determines whether roots grow deep or shallow in the soil — and could be altered to help plants adapt to changing climates. Their work has been published in the journal Cell.

In the new work, the researchers used the model plant thale cress (Arabidopsis thaliana) to identify genes and their variants that regulate the way auxin — a hormone that is a key factor in controlling the root system architecture — works. Though auxin was known to influence almost all aspects of plant growth, it was not known which factors determined how it specifically affects root system architecture.

“In order to better view the root growth, I developed and optimised a novel method for studying plant root systems in soil,” said postdoctoral fellow Takehiko Ogura, first author on the study. “The roots of A. thaliana are incredibly small so they are not easily visible, but by slicing the plant in half we could better observe and measure the root distributions in the soil.”

The team found that one gene, called EXOCYST70A3, directly regulates root system architecture by controlling the auxin pathway without disrupting other pathways. EXOCYST70A3 does this by affecting the distribution of PIN4, a protein known to influence auxin transport. When the researchers altered the EXOCYST70A3 gene, they found that the orientation of the root system shifted and more roots grew deeper into the soil.

Left: Normal Arabidopsis thaliana plant with shallow root system architecture. Right: Arabidopsis thaliana mutant showing deeper root system architecture. (Roots are coloured yellow for better visibility.) Image credit: Salk Institute.

“Biological systems are incredibly complex, so it can be difficult to connect plants’ molecular mechanisms to an environmental response,” Ogura said. “By linking how this gene influences root behaviour, we have revealed an important step in how plants adapt to changing environments through the auxin pathway.”

The findings should allow researchers to develop plants that can help combat climate change as part of Salk’s Harnessing Plants Initiative, which aims to grow plants with more robust and deeper roots that can store increased amounts of carbon underground for longer to reduce CO₂ in the atmosphere. The initiative will receive more than US$35 million from over 10 individuals and organisations through The Audacious Project to further this effort.

“We are incredibly excited about this first discovery on the road to realising the goals of the Harnessing Plants Initiative,” said Associate Professor Wolfgang Busch, senior author on the paper. “Reducing atmospheric CO₂ levels is one of the great challenges of our time, and it is personally very meaningful to me to be working toward a solution.”

In addition, the discovery could help scientists understand how plants address seasonal variance in rainfall and how to help plants adapt to changing climates. Busch said, “We hope to use this knowledge of the auxin pathway as a way to uncover more components that are related to these genes and their effect on root system architecture.

“This will help us create better, more adaptable crop plants, such as soybean and corn, that farmers can grow to produce more food for a growing world population.”

Top image caption: Takehiko Ogura and Wolfgang Busch. Image credit: Salk Institute.

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