Biotechnology Research Center and Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo 113-8657, Japan.
Proc Natl Acad Sci U S A. 2011 Dec 27;108(52):20959-64. doi: 10.1073/pnas.1116531109. Epub 2011 Dec 12.
Accumulation of cadmium (Cd) in rice (Oryza sativa L.) grains poses a potential health problem, especially in Asia. Most Cd in rice grains accumulates through phloem transport, but the molecular mechanism of this transport has not been revealed. In this study, we identified a rice Cd transporter, OsLCT1, involved in Cd transport to the grains. OsLCT1-GFP was localized at the plasma membrane in plant cells, and OsLCT1 showed Cd efflux activity in yeast. In rice plants, strong OsLCT1 expression was observed in leaf blades and nodes during the reproductive stage. In the uppermost node, OsLCT1 transcripts were detected around large vascular bundles and in diffuse vascular bundles. RNAi-mediated knockdown of OsLCT1 did not affect xylem-mediated Cd transport but reduced phloem-mediated Cd transport. The knockdown plants of OsLCT1 accumulated approximately half as much Cd in the grains as did the control plants. The content of other metals in rice grains and plant growth were not negatively affected by OsLCT1 suppression. These results suggest that OsLCT1 functions at the nodes in Cd transport into grains and that in a standard japonica cultivar, the regulation of OsLCT1 enables the generation of "low-Cd rice" without negative effects on agronomical traits. These findings identify a transporter gene for phloem Cd transport in plants.
镉（Cd）在稻米（Oryza sativa L.）中的积累对亚洲地区的人们健康构成了潜在威胁。稻米中的大部分 Cd 通过韧皮部运输积累，但这一运输的分子机制尚未被揭示。本研究中，我们鉴定了一个参与 Cd 向籽粒运输的水稻 Cd 转运蛋白 OsLCT1。OsLCT1-GFP 定位于植物细胞的质膜上，并且 OsLCT1 在酵母中表现出 Cd 外排活性。在水稻植株中，OsLCT1 在生殖期的叶片和节中表达强烈。在最上一节中，OsLCT1 转录本在大维管束周围和弥散维管束中被检测到。OsLCT1 的 RNAi 介导敲低不影响木质部介导的 Cd 运输，但降低了韧皮部介导的 Cd 运输。OsLCT1 敲低的植株在籽粒中积累的 Cd 量约为对照植株的一半。稻米中其他金属的含量和植物生长不受 OsLCT1 抑制的负面影响。这些结果表明，OsLCT1 在节点处参与 Cd 向籽粒的运输，在标准粳稻品种中，OsLCT1 的调控使“低 Cd 水稻”的产生成为可能，而不会对农艺性状产生负面影响。这些发现鉴定了植物韧皮部 Cd 运输的转运蛋白基因。
