Plants benefit from associations with a diverse community of root-colonizing microbes. Deciphering the mechanisms underpinning these beneficial services are of interest for improving plant productivity. We report a plant-beneficial interaction between Arabidopsis thaliana and the root microbiota under iron deprivation that is dependent on the secretion of plant-derived coumarins. Disrupting this pathway alters the microbiota and impairs plant growth in iron-limiting soil. Furthermore, the microbiota improves iron-limiting plant performance via a mechanism dependent on plant iron import and secretion of the coumarin fraxetin. This beneficial trait is strain specific yet functionally redundant across phylogenetic lineages of the microbiota. Transcriptomic and elemental analyses revealed that this interaction between commensals and coumarins promotes growth by relieving iron starvation. These results show that coumarins improve plant performance by eliciting microbe-assisted iron nutrition. We propose that the bacterial root microbiota, stimulated by secreted coumarins, is an integral mediator of plant adaptation to iron-limiting soils.

植物得益于与根定殖微生物的多样性社区的联系。理解支持这些有益服务的机制对于提高工厂的生产率很重要。我们报告拟南芥和根微生物在铁剥夺下的植物-有益的相互作用，这取决于植物源性香豆素的分泌。破坏该途径会改变微生物，并限制铁限制土壤中的植物生长。此外，微生物群通过依赖于植物铁输入和香豆素fraxetin分泌的机制改善了限铁植物的性能。这种有益的性状是菌株特异性的，但在整个微生物群的系统发育谱系中功能上是多余的。转录组学和元素分析表明，香樟素和香豆素之间的这种相互作用通过缓解铁饥饿来促进生长。这些结果表明，香豆素通过引起微生物辅助的铁营养来改善植物的生长性能。我们建议，由分泌的香豆素刺激的细菌根微生物群，是植物适应铁限制土壤不可或缺的媒介。