Hidden flexibility in plant communication revealed

Plants run on growth regulators, tiny chemical signals that choreograph development, but their lines of communication are more malleable than once assumed. A trio of KAUST-led studies underscore this flexibility by showing that the signaling and metabolism of specialized plant hormones known as strigolactones are regulated not by rigid locks and keys, but through enzymes and receptors capable of adapting to context and competitors.

Together, the findings point to a common theme: plants preserve control over these influential hormones by building in molecular versatility. They also broaden understanding of hormone signaling in crops and across the plant kingdom, showing that even well-mapped pathways can harbor unexpected cross-connections — and that tiny amounts of hormone act through finely tuned networks responsive to both internal cues and environmental change, with clear implications for agriculture.

“Understanding strigolactones perception and controlled catabolism is integral to optimizing crop growth and minimizing losses,” says Salim Al-Babili, a plant biochemist who co-led the studies with Stefan Arold, a structural biologist at KAUST.

“By combining structural biology with plant biochemistry, we’re revealing that these signaling systems are far more dynamic than previously thought,” adds Arold. “Flexibility, not rigidity, seems to be what gives plants such adaptive power.”

The work stems from collaborations between researchers in the Center of Excellence for Sustainable Food Security and the Center of Excellence for Smart Health at KAUST. Using Arabidopsis thaliana, a favored model organism of plant biologists, the teams explored how this modest weed manages the levels and perception of strigolactones — and in doing so, uncovered unexpected strategies that could apply across the plant kingdom.

One line of investigation zeroed in on a protein called CXE15, an enzyme newly recognized for breaking down strigolactones. Unlike similar enzymes that function alone, CXE15 is only active when two identical copies come together. The resulting dimer creates a pocket large enough to hold and cleave the hormone.

This activity is not constant, however. The KAUST team, led by Umar F. Shahul Hameed from Arold’s group and Aparna Balakrishna from Al-Babili’s group, discovered that under oxidative stress, a bond forms between the enzyme’s two halves, effectively locking it shut and stopping its activity^[1].

Consequently, plants can suspend strigolactone breakdown when conditions — such as a scarcity of essential nutrients — make higher hormone levels more useful. That ability to toggle hormone catabolism on and off provides a way for plants to fine-tune their architecture, encouraging root growth to forage for nutrients or signaling to symbiotic fungi when resources are limited.

A complementary story emerges from the receptors that sense strigolactones. These proteins, it turns out, can also take on more than one role. In a separate study, Al-Babili, Arold, and their colleagues found that a growth regulator called zaxinone binds directly to the strigolactone receptor DWARF14. By competing with strigolactones for the same site, zaxinone blocks the receptor’s usual handshake with partner proteins and dampens strigolactone signaling^[2].

“We finally solved the enigma of the connection between zaxinone and strigolactones,” says Juan C. Moreno, a plant molecular biologist in Al-Babili’s group at KAUST, and lead author of the study. “These findings not only show that a receptor of a plant hormone can bind different growth regulators, but also unravel, for the first time, a protein interaction partner for zaxinone,” he explains.

The third study takes this insight even further, showing how perception of strigolactones is translated into action. Using cryogenic electron microscopy, the KAUST team, led by Alexandra Vancea from Arold’s group, revealed the structure and dynamics of the protein complex that forms after the strigolactone is bound and processed by its receptor. The structural snapshots of this receptor–ligase–substrate complex reveal that strigolactone hydrolysis triggers a sequence of flexible, cooperative interactions among the three proteins, turning a fleeting chemical signal into a genetic response^[3].

This work shows that even this key step of signaling depends on dynamic molecular choreography, not static binding — echoing the same theme of flexibility that runs through all three discoveries.

The three studies reveal that from hormone breakdown to receptor signaling, plants rely on adaptable molecular assemblies to fine-tune their growth and environmental responses.

Taken together, these advances change the framing of strigolactone biology. Regulation does not occur solely through biosynthesis or simple receptor turnover. Instead, plants employ specialized enzymes whose activity can be switched off under stress, receptors that can accommodate structurally distinct metabolites competing for control, and signaling assemblies that dynamically adjust their configuration to fine-tune gene expression.

For agriculture, these insights could one day inform strategies to design crops with greater resilience or more finely tuned architecture — reducing vulnerability to parasitic weeds or enhancing beneficial fungal partnerships. And for plant biology, they are a reminder that even the most intensively studied laboratory species still hold molecular secrets capable of reshaping scientific dogma.

Reference

1. Shahul Hameed, U.F., Balakrishna, A., Wang, J.Y., Alvarez, D., Momin, A.A., Schwarzenberg, A., Al-Babili, S. & Arold, S.T. Molecular basis for catalysis and regulation of the Strigolactone catabolic enzyme CXE15. Nature Communications 16, 10290 (2025).| article.
2. Moreno, J.C., Hameed, U.S., Balakrishna, A. Ablazov, A. Liew, K.X., Jamil, M., Mi, J., Alashoor, K., de Saint Germain, A., Arold, S.T. & Al-Babili, S. Arabidopsis response to the apocarotenoid zaxinone involves interference with strigolactone signaling via binding to DWARF14. Nature Communications 16, 8789 (2025).| article.
3. Vancea, A.I., Huntington, B., Steinchen, W., Savva. C.G., Shahul Hameed, U.F., Arold, S.T. Mechanism of cooperative strigolactone perception by the MAX2 ubiquitin ligase–receptor–substrate complex. Nat Commun 16, 10291 (2025).| article.

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