Expression profiles of Arabidopsis thaliana in mineral deficiencies reveal novel transporters involved in metal homeostasis

Plants directly assimilate minerals from the environment and thus are key for acquisition of metals by all subsequent consumers. Limited bio-availability of copper, zinc and iron in soil decreases both the agronomic productivity and the nutrient quality of crops. Understanding the molecular mechanisms underlying metal homeostasis in plants is a prerequisite to optimizing plant yield and metal nutrient content. To absorb and maintain a balance of potentially toxic metal ions, plants utilize poorly understood mechanisms involving a large number of membrane transporters and metal-binding proteins with overlapping substrate specificities and complex regulation. To better understand the function and the integrated regulation, we analyzed in Arabidopsis the expression patterns in roots and in leaves of 53 genes coding for known or potential metal transporters, in response to copper, zinc, and iron deficiencies in Arabidopsis. Comparative analysis of gene expression profiles revealed specific transcriptional regulation by metals of the genes contrasting with the known wide substrate specificities of the encoded transporters. Our analysis suggested novel transport roles for several gene products and we used functional complementation of yeast mutants to correlate specific regulation by metals with transport activity. We demonstrate that two ZIP genes, ZIP2 and ZIP4, are involved in copper transport. We also present evidence that AtOPT3, a member of the oligopeptide transporter gene family with significant similarities to the maize iron-phytosiderophore transporter YS1, is regulated by metals and heterologous expression AtOPT3 can rescue yeast mutants deficient in metal transport.