Key Takeaways
Some plants have a reproductive strategy at the cellular level that can adapt to changing environments.
As part of that strategy, different parts of the plant are triggered by the same molecular signal, to either flower or continue to grow.
Penn researchers and colleagues have identified how plants balance the flowering versus growth response by mapping the dynamic relationships among several proteins: FT, TFL1, and LFY.
Understanding these relationships can pave the way for better crop yield.
Once a seed germinates, it is committed to one location. Plants are sessile—stuck where they started out—forced to cope with whatever conditions arrive next. The only way out of trouble is to rebuild themselves in place.
"They have to tune their form to the environment," says Doris Wagner , a plant biologist at the University of Pennsylvania . "That flexibility, often called developmental plasticity, allows plants to survive much of what nature throws its way."
Throughout a growing season, plants face a strategic choice. Some race to bloom, converting their shoot tips into flowers to produce seeds quickly—a "one and done" strategy common in (determinate) crops like rice. This works well in predictable seasons but is a gamble, as once the tip becomes a flower, no new leaves or branches can grow.
Others, like the popular model species Arabidopsis studies by Wagner, engage in a longer game: They flower on their flanks but protect the stem cells at their very tips, allowing them to keep growing and flowering continuously for weeks or months (indeterminate).
Continuous flower production can have big advantages, says Wagner, director of the Plant Adaptability and Resilience Center . "If the window of optimal conditions shifts during the season, continuous flowering increases the chances that at least some seeds are produced."
However, how indeterminate plants are able to produce flowers in some parts and prevent flowering in others when the whole plant is exposed to the same environmental cues has been been a mystery.
Now, Wagner and colleagues have determined the molecular mechanisms that enable indeterminate plants to switch to flower production in some tissues in response to environmental cues, while maintaining this switch in the off state in others to allow for continuous flowering.
Their findings, published in Science , point to new ways of understanding—and eventually tuning—plant architecture, writ large, in the face of increasingly variable environments, such as those associated with climate change.
"This shows that certain plants aren't making a single, all-or-nothing 'decision,'" says Wagner. "They're continuously measuring environmental signals and adjusting different parts of the shoot in different ways, which gives them resilience when conditions change."
To understand how plants do this, Wagner's team looked at the shoot apical meristem. This meristem, housed at the very tip of the shoot, can be likened to the plant's "engine room"—a small patch of stem cells that ensures continued growth and gives rise to other meristems that become leaves, stems, or flowers.
Typically, plants start to flower in response to environmental cues such as longer days and warmer temperatures. These cues promote the production of mobile molecular signals—most notably, the small protein florigen (FT), which travels throughout the plant's vascular system, triggering flowering across the shoot.
Focusing on FT's molecular "cousin," another small protein called TFL1, which blocks flower formation, the team found that as seasonal cues intensify, TFL1 levels rise specifically in the shoot tip, scaling with the strength of FT, the flowering signal, and effectively shielding the tip from becoming a flower.
Meanwhile, in other parts of the shoot, levels of a third factor called LEAFY (LFY) rise in response to FT and trigger flower formation.
The researchers were surprised to find that LFY levels also increase in response to seasonal cues and FT at the shoot tip but do not trigger flower formation. Instead, LFY takes on a new role.
"Somewhat counterintuitively, we noticed that LFY at the shoot tip activates TFL1," Wagner says. "And the two form a negative feedback loop."
In the shoot tip, this loop acts like a biological thermostat, with LFY as a controller. Stronger flowering signals (more FT) lead to higher LFY levels. LFY rapidly drives an increase in TFL1, which, in turn, lowers LFY accumulation. This prevents the shoot tip from crossing the threshold into flower formation, preserving the stem cells for future growth.
By partnering with mathematical modelers, the team found that this LFY-TFL1 loop is incredibly "robust." It works across a wide range of conditions, ensuring the meristem doesn't accidentally "trip" into flowering during a brief environmental fluctuation.
"It ensures that the shoot tip does not turn into a flower even when cues vary," Huang says.
Understanding this architecture offers a toolkit for the future. As climate change makes growing seasons less predictable, farmers may need crops that can similarly "hedge their bets" more effectively.
"A response to climate change shouldn't be converting more natural land into farmland," Wagner says. "It should be using the land we already farm more efficiently."
Doris Wagner is the DiMaura Professor of Biology in the University of Pennsylvania School of Arts & Sciences .
Tian Huang is a graduate student in the Wagner Lab at Penn Arts & Sciences.
Other authors include Sandhan Prakash from the Wagner Lab; Charles Hodgens and Rosangela Sozzani of North Carolina State University at Raleigh; Marco Marconi and Krzysztof Wabnik of Universidad Politécnica de Madrid.
This work received support from the National Science Foundation (Grants IOS 2319036, NSF PGRP BIO-2112058), Ministerio de Ciencia Innovación y Universidades of Spain (Grants PID2021-122158NB-I00 and CNS2023-143915), and the Agencia Estatal de Investigación of Spain (Grant CEX2020-000999-S).
