Involvement of NRAMP1 from Arabidopsis thaliana in iron transport

Nramp genes code for a widely distributed class of proteins involved in a v ariety of processes, ranging from the control of susceptibility to bacteria l infection in mammalian cells and taste behaviour in Drosophila to mangane se uptake in yeast. Some of the NRAMP proteins in mammals and in yeast are capable of transporting metal ions, including iron. In plants, iron transpo rt was shown to require a reduction/Fe(II) transport system. In Arabidopsis thaliana this process involves the IRT1 and Fro2 genes. Here we report the sequence of five NRAMP proteins from A. thaliana. Sequence comparison sugg ests that there are two classes of NRAMP proteins in plants: A. thaliana (A t) NRAMP1 and Oriza sativa (Os) NRAMP1 and 3 (two rice isologues) represent one class, and AtNRAMP2-5 and OsNRAMP2 the other. AtNramp1 and OsNramp1 ar e able to complement the fet3fet4 yeast, mutant defective both in low- and high-affinity iron transports, whereas AtNramp2 and OsNramp2 fail to do so. In addition, AtNramp1 transcript, but not AtNramp2 transcript, accumulates in response to iron deficiency in roots but not in leaves. Finally, overex pression of AtNramp1 in transgenic A. thaliana plants leads to an increase in plant resistance to toxic iron concentration. Taken together, these resu lts demonstrate that AtNramp1 participates in the control of iron homoeosta sis in plants.