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A ferric-chelate reductase for iron uptake from soils

Abstract

Iron deficiency afflicts more than three billion people worldwide1, and plants are the principal source of iron in most diets. Low availability of iron often limits plant growth because iron forms insoluble ferric oxides, leaving only a small, organically complexed fraction in soil solutions2. The enzyme ferric-chelate reductase is required for most plants to acquire soluble iron. Here we report the isolation of the FRO2 gene, which is expressed in iron-deficient roots of Arabidopsis. FRO2 belongs to a superfamily of flavocytochromes that transport electrons across membranes. It possesses intramembranous binding sites for haem and cytoplasmic binding sites for nucleotide cofactors that donate and transfer electrons. We show that FRO2 is allelic to the frd1 mutations that impair the activity of ferric-chelate reductase3. There is a nonsense mutation within the first exon of FRO2 in frd1-1 and a missense mutation within FRO2 in frd1-3. Introduction of functional FRO2 complements the frd1-1 phenotype in transgenic plants. The isolation of FRO2 has implications for the generation of crops with improved nutritional quality and increased growth in iron-deficient soils.

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Figure 1: The sequence and predicted structure of FRO2.
Figure 2: FRO2 mutations in ferric-chelate reductase-deficient frd1 Arabidopsis and the influence of iron on growth.
Figure 3: Assays of ferric-chelate reductase activity in wild type (Columbia gl1), frd1-1 mutants and transgenic frd1-1 mutants containing FRO2, showing that FRO2 complements the frd1 mutant phenotype.
Figure 4: Semiquantitative RT-PCR showing FRO2 transcript abundance in roots.

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Acknowledgements

We thank Q. J. Groom, funded by BBSRC (N.J.R.), whose work provided a basis for this study. This work was supported by a BBSRC studentship (C.M.P.) and a grant from the US National Science Foundation (M.L.G.).

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Correspondence to Nigel J. Robinson.

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Robinson, N., Procter, C., Connolly, E. et al. A ferric-chelate reductase for iron uptake from soils. Nature 397, 694–697 (1999). https://doi.org/10.1038/17800

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