Plants use a chemical 'double agent' to balance growth and survival

Science · Published 19 October 2026 · Updated 20 October 2026 Swipe more like this →

In short: Strigolactones are master regulators of plant life, but they play a dangerous game of chemical signaling. While they help plants find nutrients and manage their own architecture, they also act as a beacon for parasites, triggering the germination of invasive species that feed on the host's roots.

Strigolactones (SLs) are a diverse class of phytohormones derived from the catabolism of carotenoids. They are essential for determining a plant's physical structure, specifically by inhibiting shoot branching and patterning root and shoot architecture. They also facilitate vital symbiotic relationships, such as the growth of arbuscular mycorrhizal fungi, which provide the plant with essential soil nutrients like phosphate. These roles are managed through complex 'crosstalk' with other hormones, including auxins, cytokinins, and gibberellins, where SLs can act synergistically or antagonistically to elicit specific physiological responses.

The chemical structure of these hormones is highly specific. Canonical strigolactones feature a four-ring system (A, B, C, and D), where the D ring is highly conserved across species and is believed to be the primary site of biological activity. In contrast, non-canonical types like carlactone-type SLs lack the B and C rings. Interestingly, while they share similar bioactivities with karrikins (compounds from smoke), plants have evolved distinct receptors—such as D14—that allow them to distinguish between these two different molecular cues.

The ecological stakes of strigolactone signaling are high. Because SLs are exuded into the rhizosphere as root exudates, they serve as a chemical cue for parasitic plants like Striga lutea. These parasites detect the trace amounts of strigolactones (as low as 5 parts per million) to trigger their germination. Recent research has identified new complexities in this system, such as zaxinone, an antagonist that binds to the D14 receptor, and the discovery of specific enzymes that break down strigolactones to regulate their levels in the plant.

Understanding these mechanisms is critical for agriculture. Because strigolactones are known to induce the germination of parasitic organisms, they are considered a primary target for developing biological and chemical methods to prevent parasitic colonization. By manipulating the signaling pathways or the degradation of these hormones, scientists hope to protect crops without disrupting the beneficial symbiotic interactions that keep plants healthy.

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