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

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 AtNramp cDN As from Arabidopsis and show that these genes complement the phenotype of a metal uptake deficient yeast strain, smf1. AtNramps show homology to the N ramp gene family in bacteria, yeast, plants, and animals. Expression of AtN ramp cDNAs increases Cd2+ sensitivity and Cd2+ accumulation in yeast. Furth ermore, AtNramp3 and AtNramp4 complement an iron uptake mutant in yeast. Th is suggests possible roles in iron transport in plants and reveals heteroge neity in the functional properties of Nramp transporters. In Arabidopsis, A tNramps are expressed in both roots and aerial parts under metal replete co nditions. Interestingly, AtNramp3 and AtNramp4 are induced by iron starvati on. Disruption of the AtNramp3 gene leads to slightly enhanced cadmium resi stance of root growth. Furthermore, overexpression of AtNramp3 results in c admium hypersensitivity of Arabidopsis root growth and increased accumulati on of Fe, on Cd2+ treatment. Our results show that Nramp genes in plants en code metal transporters and that AtNramps transport both the metal nutrient Fe and the toxic metal cadmium.