A novel family of magnesium transport genes in Arabidopsis

Magnesium (Mg2+) is the most abundant divalent cation in plant cells and plays a critical role in many physiological processes. We describe the identification of a 10-member Arabidopsis gene family (AtMGT) encoding putative Mg2+ transport proteins. Most members of the AtMGT family are expressed in a range of Arabidopsis tissues. One member of this family, AtMGT1, functionally complemented a bacterial mutant lacking Mg2+ transport capability. A second member, AtMGT10, complemented a yeast mutant defective in Mg2+ uptake and increased the cellular Mg2+ content of starved cells threefold during a 60-min uptake period. Ni-63 tracer studies in bacteria showed that AtMOT1 has highest affinity for Mg2+ but may also be capable of transporting several other divalent cations, including Ni2+, Co2+, Fe2+, Mn2+, and Cu2+. However, the concentrations required for transport of these other cations are beyond normal physiological ranges. Both AtMGT1 and AtMGT10 are highly sensitive to Al3+ inhibition, providing potential molecular targets for Al3+ toxicity in plants. Using green fluorescence protein as a reporter, we localized AtMGT1 protein to the plasma membrane in Arabidopsis plants. We suggest that the AtMGT gene family encodes a Mg2+ transport system in higher plants.