In a career-defining paper, Scott Poethig, a biologist at the School of Arts & Sciences, has discovered that a single molecular switch can freeze plants in their juvenile state.
2 min. read
In the animal kingdom, some species live like Peter Pan: They never grow up. For example, the axolotl, native to Mexico, keeps its juvenile features even after reaching reproductive maturity. This phenomenon is called neoteny, and if it happened in humans, we would look like toddlers for our entire lives.
But neoteny isn’t just limited to animals. In fact, it’s surprisingly common in plants, too.
Some plants, like the flowering acacia (pictured right), keep their juvenile features even after reaching reproductive maturity, a phenomenon called neoteny that biology professor Scott Poethig (pictured left) has spent a career studying.
(Images: Left: Jia He; right: courtesy of Omnia)
“Plants probably have more examples of neoteny than animals,” says Scott Poethig, John H. and Margaret B. Fassitt Professor Emeritus of Biology. In career-culminating research published in the Proceedings of the National Academy of Sciences, Poethig uncovered the genetic underpinnings behind neoteny in plants. The work reveals how a single molecular switch can freeze a plant in its juvenile state—a finding Poethig says holds big implications for conservation, horticulture, and more.
Poethig first became fascinated by plants in graduate school, when he investigated corn mutants. His later work in Arabidopsis, a small plant in the mustard family, led to the discovery of a molecule that controls when plants develop their adult features. The molecule, called miR156, is a type of microRNA, a class of RNA that helps regulate gene expression.
It turns out, according to Poethig’s work, that miR156 is key for the juvenile-to-adult transition for Arabidopsis. This transition is separate from reproductive maturity, and generally involves physical traits that help the plant adapt to different stages of its life. For example, juvenile leaves in some plant species may be better suited for rapid growth in moist, competitive environments, whereas adult leaves fare well in dry, high-light conditions.
Poethig found that Arabidopsis contained high levels of miR156 as juveniles, which prevented the genes associated with adult traits from expressing, but those levels naturally decreased into adulthood. By analyzing RNA in juvenile and adult samples of eucalyptus from San Francisco, acacia trees from Australia, and ivy and oak from Penn’s own campus, Poethig confirmed miR156 levels controlled the juvenile-to-adult transition in plants all around the world.
“Every plant does this, and nobody had figured out the mechanism before,” Poethig says.
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