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Poster

Session: Session 2 Presenting Authors at Posters (Odds)

P-261 - Root-secreted coumarin promotes Fe nutrition of coumarin-tolerant rhizobacteria

Wednesday, July 16, 2025
13:30 - 15:15  
Location: Confex Hall 3
Nutrient exchange & role of metabolites in plant-microbe interactions
Abstract Text: Plant roots secrete secondary metabolites to shape the root environment to their benefit. In soils with circumneutral pH, roots secrete antimicrobial coumarins that chelate and reduce Fe oxides. Once secreted, these coumarins can enhance plant Fe nutrition, and alter the microbial life in the rhizosphere, potentially benefiting plant health. How coumarins affect these microbes is unknown. Understanding this can help us understand how plants regulate their functional microbiome. To investigate the mechanisms of coumarin tolerance, we employed an RB-TnSeq approach using the coumarin-resistant, plant-beneficial Pseudomonas simiae WCS417. Focusing on the most secreted coumarins, scopoletin and the Fe-chelating fraxetin, this allowed us to identify mutants that lost their tolerance. Mutants of genes related to Fe uptake and efflux pumps exhibited reduced survival under fraxetin-rich conditions. Interestingly, fraxetin enhanced WCS417 growth in an Fe-dependent manner and rescued the lagging growth of a WCS417 siderophore mutant, highlighting its role in Fe nutrition. Using the Netherlands Plant Eco-phenotyping Centre, we show that mCherry-tagged WCS417 colonizes Arabidopsis in a coumarin-dependent manner, particularly in circumneutral pH, where fraxetin is predominantly secreted. These results show that fraxetin facilitates inter-kingdom Fe nutrition and may play a role in  regulating beneficial interactions between Arabidopsis thaliana and Pseudomonas rhizobacteria.