The IRT1 protein from Arabidopsis thaliana is a metal transporter with a broad substrate range

The molecular basis for the transport of manganese across membranes in plan t cells is poorly understood. We have found that IRT1, an Arabidopsis thali ana metal ion transporter, can complement a mutant Saccharomyces cerevisiae strain defective in high-affinity manganese uptake (smf1 Delta). The IRT1 protein has previously been identified as an iron transporter. The current studies demonstrated that IRT1, when expressed in yeast, can transport mang anese as well. This manganese uptake activity was inhibited by cadmium, iro n(II) and zinc, suggesting that IRT1 can transport these metals. The IRT1 c DNA also complements a zinc uptake-deficient yeast mutant strain (zrt1zrt2) , and IRT1-dependent zinc transport in yeast cells is inhibited by cadmium, copper, cobalt and iron(III). However, IRT1 did not complement a copper up take-deficient yeast mutant (ctr1), implying that this transporter is not i nvolved in the uptake of copper in plant cells. The expression of IRT1 is e nhanced in A. thaliana plants grown under iron deficiency. Under these cond itions, there were increased levels of root-associated manganese, zinc and cobalt, suggesting that, in addition to iron, IRT1 mediates uptake of these metals into plant cells. Taken together, these data indicate that the IRT1 protein is a broad-range metal ion transporter in plants.