Abstract
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.
Highlights
All organisms require metal prosthetic groups for their unique catalytic and structural properties
We focus on the changes in expression of genes coding for transporters and metal homeostasis proteins that are present on the 8.3K Arabidopsis DNA chip and were shown previously or in this study to be regulated in response to copper, zinc, and iron deficiency
Our results showed that ZIP genes can be regulated by zinc (ZIP4, ZIP5, ZIP9), iron (IRT2), and copper (ZIP2 and ZIP4) both in the roots and in the leaves (Table IIA and Figs. 1 and 2)
Summary
Plant Growth—Arabidopsis thaliana Columbia were aseptically grown on hydroponics at 20 °C under a 16-h light/8-h dark cycle. Plants were grown for 5 days on HEDTA-buffered copper-deficient medium before the roots and the leaves were harvested for RNA extraction. Plants were germinated and grown on control growth medium (containing zinc). Plants were grown for 5 days on the HEDTAbuffered zinc-deficient medium before the roots and leaves were harvested for RNA extraction. Plants were germinated and grown for 5 weeks on control growth medium, after which the medium was replaced by control medium lacking FeSO4/EDTA but containing 50 M ferrozine to capture trace iron contamination. A two-sample t test was performed (separately for leaves or for roots) to obtain genes which ADI statistically differed between the treatments and their corresponding controls (p Ͻ 0.15). Yeast mutants were grown in SD medium lacking divalent ions supplemented with the appropriate amino acids and metal salts containing either glucose (2%) or glycerol (2%). Copper content was analyzed by ICP-atomic emission spectrometry at 224 nm
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