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From morning glories spiraling up fence posts to grape vines corkscrewing through arbors, twisted growth is a problem-solving tool found throughout the plant kingdom. Scientists have discovered that roots often “do the twist” to navigate around rocks and other debris. This phenomenon, long observed but not fully understood, has taken a new turn with recent scientific discoveries.
Researchers at Washington University in St. Louis, led by Ram Dixit, have uncovered a key mechanism behind this twisting growth. Their findings, published in Nature Communications, reveal that a change in gene expression specifically in the plant epidermis, rather than a complete gene mutation, can lead to this widespread growth habit.
Understanding the Genetic Twist
Scientists have known that mutations in certain genes affecting microtubules can cause plants to grow in a twisting manner. These are often “null mutations,” where the absence of a particular gene results in this growth pattern. However, the persistence of twisted growth as a common evolutionary adaptation puzzled researchers like Dixit, the George and Charmaine Mallinckrodt Professor of Biology.
With the help of his former PhD student Natasha Nolan and Guy Genin from the WashU McKelvey School of Engineering, Dixit discovered that a full null mutation is unnecessary for twisting. Instead, the twist can occur with a change in gene expression in the plant’s epidermis alone. “That might explain why this is so widespread: you don’t need null mutations for this growth habit, you just need ways to tweak certain genes in the epidermis alone,” Dixit explained.
The Role of Mechanobiology
This research emerged from the National Science Foundation Science and Technology Center for Engineering Mechanobiology (CEMB), a nationwide consortium co-led by WashU. The center brings together biologists, engineers, and physicists to understand how physical forces shape living systems. “This discovery is a perfect example of what our center was designed to do,” said Genin, co-director of CEMB. By combining biological experiments with mechanical modeling, the team uncovered a fundamental principle: the outermost layer of the root dominates its twisting behavior.
“Geometry matters enormously,” Genin emphasized, explaining that the outer ring of cells in concentric layers has far more leverage over the whole structure than the inner rings.
Implications for Agriculture
Beyond an evolutionary curiosity, understanding how roots navigate soil is increasingly urgent. As climate change intensifies droughts and pushes agriculture onto marginal lands with rocky, compacted soils, crops with adaptable root systems are becoming critical. “Roots are the hidden half of agriculture,” noted Charles Anderson, a professor of biology and CEMB leader at Pennsylvania State University. “A plant’s ability to find water and nutrients depends entirely on how its roots explore the soil.”
Twisted growth also plays roles in how vines climb, how stems resist wind, and how plants anchor themselves against erosion—factors crucial for food security and ecosystem resilience.
Solving the Mystery
Nolan’s research focused on a model plant system where roots can skew right or left. The team hypothesized that twists emerge from the inner cortical layer, where mutation causes cells to be short and wide. However, they discovered that expressing the wild-type gene in the epidermis alone could restore straight roots, indicating that the epidermis dictates this behavior.
Anderson’s lab measured the orientation of cellulose microfibrils in mutant and wild-type roots, finding that twisty defects alter cellulose deposition. Genin used this data to create a computer model explaining why the epidermis dominates. “Our model showed that if only the epidermis has skewed cell files, it can drive about one-third of the total twisting,” Genin explained.
“The math was unambiguous: the outer layer rules,” Genin concluded.
The model confirmed that the epidermis, rather than being a passive skin, acts as a mechanical coordinator of growth. “Somehow the epidermal cell layer is able to entrain inner cell layers,” Dixit said.
Future Directions in Plant Engineering
With this new understanding, scientists can apply these findings to agricultural challenges. “Imagine being able to design plants that dial up or dial down a root’s tendency to twist,” Anderson suggested. This research provides a target and mechanical framework for considering root architecture as an engineering problem.
Genin highlighted the importance of interdisciplinary collaboration: “A biologist alone might have found that the epidermis matters, but wouldn’t have had the tools to explain why. An engineer alone couldn’t have done the genetics and phenotyping. Together, as a center, we got the full picture.”
The study, “The epidermis coordinates multi-scale symmetry breaking in chiral root growth,” was supported by the Center for Engineering Mechanobiology and the National Institute of General Medical Sciences. The research opens new avenues for developing crops that can thrive in challenging environments, addressing both agricultural and ecological needs.
