Cadmium and iron transport by members of a plant metal transporter family in <i>Arabidopsis</i> with homology to <i>Nramp</i> genes

<jats:p> Metal cation homeostasis is essential for plant nutrition and resistance to toxic heavy metals. Many plant metal transporters remain to be identified at the molecular level. In the present study, we have isolated <jats:italic>AtNramp</jats:italic> cDNAs from <jats:italic>Arabidopsis</jats:italic> and show that these genes complement the phenotype of a metal uptake deficient yeast strain, <jats:italic>smf1</jats:italic> . <jats:italic>AtNramp</jats:italic> s show homology to the <jats:italic>Nramp</jats:italic> gene family in bacteria, yeast, plants, and animals. Expression of <jats:italic>AtNramp</jats:italic> cDNAs increases Cd <jats:sup>2+</jats:sup> sensitivity and Cd <jats:sup>2+</jats:sup> accumulation in yeast. Furthermore, <jats:italic>AtNramp3</jats:italic> and <jats:italic>AtNramp4</jats:italic> complement an iron uptake mutant in yeast. This suggests possible roles in iron transport in plants and reveals heterogeneity in the functional properties of <jats:italic>Nramp</jats:italic> transporters. In <jats:italic>Arabidopsis</jats:italic> , <jats:italic>AtNramps</jats:italic> are expressed in both roots and aerial parts under metal replete conditions. Interestingly, <jats:italic>AtNramp3</jats:italic> and <jats:italic>AtNramp4</jats:italic> are induced by iron starvation. Disruption of the <jats:italic>AtNramp3</jats:italic> gene leads to slightly enhanced cadmium resistance of root growth. Furthermore, overexpression of <jats:italic>AtNramp3</jats:italic> results in cadmium hypersensitivity of <jats:italic>Arabidopsis</jats:italic> root growth and increased accumulation of Fe, on Cd <jats:sup>2+</jats:sup> treatment. Our results show that <jats:italic>Nramp</jats:italic> genes in plants encode metal transporters and that <jats:italic>AtNramps</jats:italic> transport both the metal nutrient Fe and the toxic metal cadmium. </jats:p>