Localization of MT2a Gene Promoter Expression Is Different from the Site(s) of Copper Accumulation in the Roots of Transgenic Arabidopsis thaliana

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Accumulation of mRNA for MT2a, a metallothionein of Arabidopsis thaliana, is known to be upregulated by excess copper (Cu). We compared the localization of the promoter activity of the MT2a gene and the accumulation site(s) of Cu in the roots of transgenic A. thaliana. Open reading frame of the β-glucuron-idase (GUS) gene was fused with the MT2a gene promoter and introduced into A. thaliana. Strong GUS activity was observed in the region near or within the stele in the presence of Cu at a high concentration (high-Cu condition). Electron probe X-ray micro-analysis demonstrated that under high-Cu conditions, Cu accumulated most abundantly in the cortex, where GUS activity was not significantly induced. These results indicate that the sites showing the MT2a promoter activity and Cu accumulation did not coincide with each other, suggesting that Cu is not a direct activator of the MT2a promoter.
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