Sammy Westfall

When the sun sets, plants have no eyes to see it. When the sun rises, there’s not even a blink.

Like biological clockwork, however, plants respond to the day-night cycle as if they could actually witness the pink-blue-black of a coming dusk.

This response is part of a complex system of receptor proteins that scientists have spent years trying to understand. In a new Yale study published on Aug. 21 in Nature Communications, they’ve come one step closer.

When the sun finally ducks under the horizon, the thale cress plant can balance its energy use and control flowering, among other processes, thanks to a light-detecting protein called ZEITLUPE. The protein builds up during the day, amassing its forces, and then launches on various other proteins in the cell once night falls, halting processes that should only be done when the sun’s out.

Joshua Gendron, leader of the Gendron Lab at Yale and senior author of the study, said the day-night cycle — called the circadian clock — is important to plants in much the same way that it is for humans.

Just as we get jet lag from flying to different time zones, plants “also get jet lag if their circadian clock is malfunctioning or out of sync with the environment,” Gendron said. “But for them, this is a death sentence because they can’t defend themselves against herbivores and will be quickly eaten.”

Previously, according to postgraduate associate Ann Feke GRD ’19, scientists weren’t exactly sure how ZEITLUPE could halt its attack once the night ends. But by carefully breeding the plant species and growing them under a light system that mimics dusk and dawn, the Gendron Lab found an answer.

Two other proteins, called ubiquitin-specific protease 12 and 13, are responsible for reigning ZEITLUPE in, according to the study. Without them, the plant wouldn’t be able to time its energy use to the sunset — which can have disastrous effects, Gendron said.

“If they can’t figure this out they either starve or keep too much energy in reserve,” he explained.

Feke said the discovery is important for farming, which depends on plants’ day-night cycles for good harvests. “Plants are finely tuned to the growing environments that they evolved in,” she said. Plants from the equator may be accustomed to a different day length than those farther North.

Climate change can change the location of fertile farmland, Feke added, leading to lower harvests in places that have enjoyed the opposite. But gene editing could stand to change this.

“By learning more about the way that plants recognize seasonal changes,” she said, “we may be able to adjust the latitudes that the plants prefer, thus allowing us to maintain or even improve crop yield.”

For Gendron, the findings are especially relevant to his career. The professor in molecular, cellular and developmental biology has worked for years across the United States to learn more about the thale cress’ biological clock.

Funded in part by the National Science Foundation and the National Institutes of Health, the study also reveals further questions about climate change’s impact on plants, he said.

“We are working diligently to understand [dramatic changes in climate] from the plant’s perspective with the goal of helping our most important crops to be robust to the effects of climate change,” Gendron said.

Thale cress is generally found on the side of the road and is considered a weed.

Matt Kristoffersen | matthew.kristoffersen@yale.edu