Beyond the root: microbial partners extend plant metabolic pathways to mobilize iron.

Under iron (Fe)-limiting conditions, Arabidopsis thaliana roots secrete coumarins, phenylpropanoid-derived secondary metabolites that can mobilize sparingly available Fe and shape the composition of the root-associated microbiome. Recent studies show that microbial partners can act on root-secreted coumarins to produce forms with higher Fe-mobilization capacity. Besides providing a mechanistic understanding of the positive interaction of soil microbiota to improved plant Fe nutrition, these findings provide new evidence that the functional boundaries of plant metabolic pathways extend into the rhizosphere.