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Updated: Jul 9, 2026

A Colorimetric Method for Measuring Iron Content in Plants
Published on: September 7, 2018
Coumarins link iron deficiency to TOR inhibition in plants
Huikyong Cho1, Ilyeong Choi1, Sachi Horibata2
1Plant Resilience Institute, Michigan State University, East Lansing, MI 48824, USA; Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, MI 48824, USA.
Abstract:
The target of rapamycin (TOR) is a conserved master regulator of growth1,2 that integrates nutrient availability with developmental programs. While TOR inhibition under nutrient limitation is generally attributed to upstream signaling pathways, endogenous small-molecule regulators of TOR have not been defined in eukaryotes. Here, we show that plants use coumarins to modulate TOR activity. In Arabidopsis thaliana, we discovered that iron deficiency-induced coumarin accumulation represses TOR-S6K signaling and restricts root growth. Structural modeling and kinase activity analyses support a mechanism consistent with competition between the coumarin esculetin and ATP for binding to the catalytic pocket. Together, these findings identify specialized metabolites as modulators of TOR signaling, linking nutrient-responsive metabolism to growth control.
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