A ferric-chelate reductase for iron uptake from soils

Iron deficiency afflicts more than three billion people worldwide(1), and p lants are the principal source of iron in most diets. Low availability of i ron often limits plant growth because iron forms insoluble ferric oxides, l eaving only a small, organically complexed fraction in soil solutions(2). T he enzyme ferric-chelate reductase is required for most plants to acquire s oluble iron. Here we report the isolation of the FRO2 gene, which is expres sed in iron-deficient roots of Arabidopsis. FRO2 belongs to a superfamily o f flavocytochromes that transport electrons across membranes. It possesses intramembranous binding sites for haem and cytoplasmic binding sites for nu cleotide cofactors that donate and transfer electrons. We show that FRO2 is allelic to the frd1 mutations that impair the activity of ferric-chelate r eductase(3). 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 funct ional FRO2 complements the frd1-1 phenotype in transgenic plants. The isola tion of FRO2 has implications for the generation of crops with improved nut ritional quality and increased growth in iron-deficient soils.