Kim Do-Young, Bovet Lucien, Maeshima Masayoshi, Martinoia Enrico, Lee Youngsook
POSTECH-UZH Cooperative Laboratory, Division of Molecular Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
Plant J. 2007 Apr;50(2):207-18. doi: 10.1111/j.1365-313X.2007.03044.x. Epub 2007 Mar 12.
Cadmium (Cd) and lead (Pb) are widespread pollutants that are toxic to plant growth. The expression of AtPDR8 was upregulated in cadmium- or lead-treated Arabidopsis thaliana. To test whether AtPDR8 is involved in heavy metal resistance, we examined transgenic Arabidopsis that over-expressed AtPDR8 and RNAi plants that exhibited a severely reduced AtPDR8 transcript level, as well as T-DNA insertion mutants of this ABC transporter. AtPDR8-over-expressing plants were more resistant to Cd(2+) or Pb(2+) than the wild-type and had lower Cd contents. In contrast, AtPDR8 RNAi transgenic plants and T-DNA insertion lines were more sensitive to Cd(2+) or Pb(2+) compared to wild-type plants and had higher Cd contents. The GFP-AtPDR8 protein was targeted to the plasma membrane, and GUS activity was present in most cells but strongest in the root hair and epidermal cells. Cd extrusion was higher in the AtPDR8-over-expressing plants in a flux assay using isolated protoplasts and radioactive (109)Cd, and was lower in the RNAi transgenic plants than in the wild-type. Together, these data strongly support a role for AtPDR8 as an efflux pump of Cd(2+) or Cd conjugates at the plasma membrane of Arabidopsis cells. As AtPDR8 has been suggested to be involved in the pathogen response and in the transport of chemicals that mediate pathogen resistance, this ABC protein is likely to transport a very broad range of substrates.
镉（Cd）和铅（Pb）是广泛存在的污染物，对植物生长有毒害作用。在镉或铅处理的拟南芥中，AtPDR8的表达上调。为了测试AtPDR8是否参与重金属抗性，我们检测了过表达AtPDR8的转基因拟南芥、AtPDR8转录水平严重降低的RNAi植株以及该ABC转运蛋白的T-DNA插入突变体。过表达AtPDR8的植株比野生型对Cd(2+)或Pb(2+)更具抗性，且镉含量更低。相反，与野生型植株相比，AtPDR8 RNAi转基因植株和T-DNA插入系对Cd(2+)或Pb(2+)更敏感，且镉含量更高。GFP-AtPDR8蛋白定位于质膜，GUS活性在大多数细胞中都有，但在根毛和表皮细胞中最强。在使用分离原生质体和放射性(109)Cd的通量测定中，过表达AtPDR8的植株中镉的外排更高，而RNAi转基因植株中的镉外排比野生型更低。总之，这些数据有力地支持了AtPDR8作为拟南芥细胞质膜上Cd(2+)或镉结合物外排泵的作用。由于AtPDR8被认为参与病原体反应以及介导病原体抗性的化学物质的运输，这种ABC蛋白可能运输范围非常广泛的底物。
