Two genes encoding <i>Arabidopsis halleri</i> MTP1 metal transport proteins co‐segregate with zinc tolerance and account for high <i>MTP1</i> transcript levels

<jats:title>Summary</jats:title><jats:p>The zinc hyperaccumulator plant <jats:italic>Arabidopsis halleri</jats:italic> is able to naturally accumulate 100‐fold higher leaf zinc concentrations when compared with non‐accumulator species such as the closely related <jats:italic>A. lyrata</jats:italic> and <jats:italic>A. thaliana</jats:italic>, without showing toxicity symptoms. A novel member of the cation diffusion facilitator (CDF) protein family, an <jats:italic>A. halleri</jats:italic> metal tolerance protein 1 (MTP1), and the homologous <jats:italic>A. thaliana</jats:italic> Zn transporter (ZAT)/AtMTP1 metal‐specifically complement the zinc hypersensitivity of a <jats:italic>Saccharomyces cerevisiae zrc1 cot1</jats:italic> mutant strain. A fusion of the AhMTP1 protein to green fluorescent protein (GFP) localizes to the vacuolar membrane of <jats:italic>A. thaliana</jats:italic> protoplasts. When compared with <jats:italic>A. lyrata</jats:italic> and <jats:italic>A. thaliana</jats:italic>, the total <jats:italic>MTP1</jats:italic> transcript levels are substantially higher in the leaves and upregulated upon exposure to high zinc concentrations in the roots of <jats:italic>A. halleri</jats:italic>. The high <jats:italic>MTP1</jats:italic> transcript levels in <jats:italic>A. halleri</jats:italic> can be primarily attributed to two genetically unlinked genomic <jats:italic>AhMTP1</jats:italic> gene copies. The two corresponding loci co‐segregate with zinc tolerance in the back‐cross 1 generation of a cross between the zinc‐tolerant species <jats:italic>A. halleri</jats:italic> and the zinc‐sensitive species <jats:italic>A. lyrata</jats:italic>. In contrast, a third <jats:italic>MTP1</jats:italic> gene in the genome of <jats:italic>A. halleri</jats:italic> generates only minor amounts of <jats:italic>MTP1</jats:italic> transcripts and does not co‐segregate with zinc tolerance. Our data suggests that zinc tolerance in <jats:italic>A. halleri</jats:italic> involves an expanded copy number of an ancestral <jats:italic>MTP1</jats:italic> gene, encoding functional proteins that mediate the detoxification of zinc in the cell vacuole. At the transcript level, <jats:italic>MTP1</jats:italic> gene copies of <jats:italic>A. halleri</jats:italic> are regulated differentially and in response to changes in zinc supply.</jats:p>