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Biosynthesis of redox-active metabolites in response to iron deficiency in plants

Nature Chemical Biologyvolume 14pages442450 (2018) | Download Citation

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Abstract

Iron is an essential but poorly bioavailable nutrient because of its low solubility, especially in alkaline soils. Here, we describe the discovery of a previously undescribed redox-active catecholic metabolite, termed sideretin, which derives from the coumarin fraxetin and is the primary molecule exuded by Arabidopsis thaliana roots in response to iron deficiency. We identified two enzymes that complete the biosynthetic pathway of fraxetin and sideretin. Chemical characterization of fraxetin and sideretin, and biological assays with pathway mutants, suggest that these coumarins are critical for iron nutrition in A. thaliana. Further, we show that sideretin production also occurs in eudicot species only distantly related to A. thaliana. Untargeted metabolomics of the root exudates of various eudicots revealed production of structurally diverse redox-active molecules in response to iron deficiency. Our results indicate that secretion of small-molecule reductants by roots may be a widespread and previously underappreciated component of reduction-based iron uptake.

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Acknowledgements

This work was supported by US National Institutes of Health grant DP2 AT008321 and an HHMI–Simons Faculty Scholar Award to E.S.S. and by a grant from the Deutsche Forschungsgemeinschaft to N.v.W. (WI1728/21-1). J.R. was supported by an NIH Biotechnology Training Grant (T32 GM008412-20). We thank N. Schmid, J. Fuge, A. Bieber, H. Nierig, and M. Voges for valuable discussions and help with experiments; S. Elliott for advice on redox potential measurements; S. Fendorf for helpful discussions on rhizosphere iron; M. Kevin Brown and J. Du Bois for suggestions for chemical synthesis of sideretin; and T. Veltman for help with cyclic voltammetry measurements. We thank C. Curie (CNRS, IBIP, Montpellier) and M. B. Mudgett (Stanford University) for providing seeds.

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Affiliations

  1. Department of Chemical Engineering, Stanford University, Stanford, CA, USA

    • Jakub Rajniak
    • , Evelyn Chang
    •  & Elizabeth S. Sattely
  2. Department of Physiology and Cell Biology, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Gatersleben, Germany

    • Ricardo F. H. Giehl
    •  & Nicolaus von Wirén
  3. Department of Biosciences, University of Milan, Milan, Italy

    • Irene Murgia

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Contributions

J.R., R.F.H.G., N.v.W., and E.S.S. designed experiments. J.R., R.F.H.G., and E.C. performed experiments. I.M. isolated homozygous T-DNA-insertion line cyp82C4-2. J.R., R.F.H.G., E.C., N.v.W., and E.S.S. analyzed data. J.R., R.F.H.G., N.v.W., and E.S.S. wrote the paper.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to Elizabeth S. Sattely.

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https://doi.org/10.1038/s41589-018-0019-2