Rice is a major dietary source of the toxic metal cadmium (Cd), and reducing its accumulation in the grain is therefore important for food safety. We selected two cultivars with contrasting Cd accumulation and generated transgenic lines overexpressing OsNRAMP5, which encodes a major influx transporter for manganese (Mn) and Cd. We used two different promoters to control the expression, namely OsActin1 and maize Ubiquitin. Overexpression of OsNRAMP5 increased Cd and Mn uptake into the roots, but markedly decreased Cd accumulation in the shoots, whilst having a relatively small effect on Mn accumulation in the shoots. The overexpressed OsNRAMP5 protein was localized to the plasma membrane of all cell types in the root tips and lateral root primordia without polarity. Synchrotron X-ray fluorescence mapping showed that the overexpression lines accumulated more Cd in the root tips and lateral root primordia compared with the wild-type. When grown in three Cd-contaminated paddy soils, overexpression of OsNRAMP5 decreased concentration of Cd in the grain by 49–94% compared with the wild type. OsNRAMP5-overexpression plants had decreased Cd translocation from roots to shoots as a result of disruption of its radial transport into the stele for xylem loading, demonstrating the effect of transporter localization and polarity on ion homeostasis.

中文翻译：

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锰/镉转运蛋白OsNRAMP5的过表达减少了水稻籽粒中的镉积累。

大米是有毒金属镉（Cd）的主要饮食来源，因此减少其在谷物中的积累对食品安全至关重要。我们选择了两个具有相反Cd积累的品种，并生成了过表达OsNRAMP5的转基因品系，该基因编码了锰（Cd）和Cd的主要流入转运蛋白。我们使用了两种不同的启动子来控制表达，即OsActin1和玉米泛素。OsNRAMP5的过表达增加了Cd和Mn吸收到根中，但显着降低了Cd在芽中的积累，而对Mn在芽中的积累影响相对较小。过表达的OsNRAMP5蛋白位于根尖和侧根原基中所有细胞类型的质膜上，没有极性。同步辐射X射线荧光图谱显示，与野生型相比，过表达谱系在根尖和侧根原基中积累了更多的镉。当在三个Cd污染水田土壤中生长，过表达OsNRAMP5镉的浓度在晶粒由49-94％与野生型相比降低。OsNRAMP5-过表达植物由于其径向转运到木质部负载的石碑中而破坏了其从根到芽的Cd转运，这证明了转运蛋白的定位和极性对离子稳态的影响。