AMES, IA – An Iowa State University researcher has identified a protein as a key regulator of plant root growth, representing a significant step towards understanding the complex, underlying processes that influence development of root cells.
Dior Kelley, an assistant professor in the Department of Genetics, Development and Cell Biology, works in the field of proteomics, the study of proteins’ structures and functions.
Kelley’s research team specializes in researching natural hormones called auxins that help regulate many aspects of plant development. Their new findings about the role of a key auxin-regulated protein are featured in this month’s prestigious scientific journal MCP: Molecular and Cellular Proteomics — along with the cover illustration that Kelley created with her artist mother.
“Proteins are the workforce of cells. They are enzymes that have crucial metabolic functions,” said Kelley, who studies these functions in Arabidopsis, or thale cress. The plant often is used by scientists as a research model because its genetics are thoroughly understood.
The study of auxins has been underway since Charles Darwin and his son Francis started observing seedlings’ response to light more than 100 years ago, said Kelley.
Since then, scientists have learned that auxins operate as a potent growth regulator: The right amount at the right time can stimulate and elongate plant root cells. Too much can cause out-of-control growth or stunted growth — an effect useful in several farm herbicides that use synthetic auxins to control weeds in crop fields.
Still, scientists have much to understand about the ways auxins direct changes in root cells.
“It’s not just one hormone in a plant tissue. It’s really the interconnectedness of many hormones activating over time that drives growth,” Kelley said. “It gets complicated very quickly.”
Kelley’s team is teasing out some of this complexity. They identified an auxin-regulated protein, called GAUT10, as key in maintaining the zone of plant root tissue where growth occurs — the meristem. Through a series of experiments, they showed that GAUT10 plays a role in root growth and the processing of sugars, an important component of cell walls.
In the experiments, the team screened hundreds of seedling roots to identify mutants that showed observable differences from typical roots. Then, the mutants were analyzed to understand what made them different, including what made some more or less responsive to auxin exposure.
“It's a process that can be compared to a car factory,” Kelley said. “You can see what goes in and what comes out. If you wanted to know the role of each factory worker, you could remove that worker from the assembly line for a day and see what’s wrong with the cars that come out of the factory. Are the cars missing a seat belt? Are the bolts that hold the passenger-side tires in place?” she said. “That’s kind of what we’re doing — we’re holding back different elements in the pathway of a plant’s development to see what the outcome is.”
In the case of GAUT10, the results represent new information about how plant growth is simultaneously governed by intrinsic cues within plants, such as the hormone auxin, and extrinsic cues from the environment, such as carbon availability.
“Our research provides another small, but important, insight towards understanding the trajectories of root growth and aging that may inform future improvements to crop yield, a critical aspect of food security,” Kelley said. “We now understand more about the interplay between genetic potential and external factors like nutrient availability.”
The findings are published in the June 2019 issue of the peer-reviewed Molecular and Cellular Proteomics of the American Society for Biochemistry and Molecular Biology. The article’s co-authors are Michelle Lang, an undergraduate in biology at Iowa State; Justin Walley, assistant professor in ISU’s Department of Plant Pathology and Microbiology; Yunting Pu, a former ISU PhD student in genetics, development and cell biology, now a research associate at Michigan State University; and collaborators from the University of California San Diego. The research received start-up funding from Iowa State University’s College of Agriculture and Life Sciences and the Department of Genetics, Development and Cell Biology.
This is the first major publication to come out of Kelley’s ISU lab. “It’s exciting,” she said. What makes it doubly exciting is that her work is featured on the cover of the journal — and she is responsible for the issue’s cover art.
When the journal notified Kelley that her team’s article would be the focus of the cover, she consulted with her graphic artist mother, Rose Garvin, of Oregon, for ideas.
Garvin, who specializes in Feng Shui and myth, suggested an illustration of an ancient Chinese goddess. The goddess, Xiwangmu, is often pictured carrying a rootlike structure, symbolizing life and immortality. The idea resonated with Kelley -- and with the journal’s editors.
In the final cover design, a modernized Xiwangmu, with auxin molecules tattooed on her arms, holds a root, overlaid on a microscopic image of the GAUT10 mutant root. It’s easy to imagine that Garvin’s inspiration was her tattooed, scientist daughter whose work at Iowa State embodies the creative pursuit to understand growth and life.