This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A new study led by Paul Schulze-Lefert from the Max Planck Institute for Plant Breeding Research in Cologne, in collaboration with Ricardo F.H. Giehl at the Leibniz Institute of Plant Genetics and Crop Plant Research in Gatersleben, revealed how Arabidopsis plants adapt their chemical communication with the bacterial root microbiota to maximize the acquisition of bio-unavailable iron from acidic or calcareous soils.
The study is now published in Cell. Iron is essential for plant growth, yet in many soils it remains out of reach for plants. The reason is chemical: much of the iron is locked in insoluble forms that roots cannot directly absorb.
As a result, plants have evolved strategies to unlock and acquire this essential micronutrient from soils. These hidden mechanisms are crucial for healthy plant growth and, ultimately, for the productivity of the crops that sustain global food systems. All healthy plants grown in natural soils are colonized by a diverse community of microbes, known as the microbiota.
To cope with iron limitation, plants such as Arabidopsis thaliana and many crop species activate a sophisticated iron starvation response. This starvation response involves the release of specialized molecules, often coumarins, from the roots into the rhizosphere—the narrow zone of soil surrounding the plant roots and inhabited by the root microbiota. Coumarins come in different "flavors." Arabidopsis adjusts the release of different coumarin chemotypes according to soil pH: sideretin is the main coumarin secreted by roots in acidic soils, while more fraxetin is released in calcareous soils.
These chemicals can mobilize bio-unavailable iron and are thought to be an adaptation to soil pH to maximize iron acquisition. Yet paradoxically, plants grown without their bacterial root microbiota remain iron-deficient. Previous studies have shown that root-associated bacteria can help plants overcome iron deficiency, with fraxetin playing a key role in calcareous soils at near-neutral pH.
However, it remained unclear whether root-associated bacteria support pH-adaptive iron acquisition—together with the different coumarins released—and how these coumarins interact with the bacteria. Using genetic and chemical approaches in plants and bacteria, the team found that sideretin and fraxetin interact with a wide range of root-associated bacteria and help mobilize iron in the soil, making it more accessible to the plant. Importantly, while the pH-adapted release of these coumarins by the plant occurs in the absence of microbes, their full function in iron mobilization is only seen in synergy with the root microbiota.
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