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Excessive cadmium (Cd) accumulation in grains of rice (Oryza sativa L.) is a risk to food security. The transporters in the nodes of rice are involved in the distribution of mineral elements including toxic elements to different tissues such as grains. However, the mechanism of Cd accumulation in grains is largely unknown. Here, we report a node-expressed transporter gene, OsCCX2, a putative cation/calcium (Ca) exchanger, mediating Cd accumulation in the grains of rice. Knockout of OsCCX2 caused a remarkable reduction of Cd content in the grains. Further study showed that disruption of this gene led to a reduced root-to-shoot translocation ratio of Cd. Moreover, Cd distribution was also disturbed in different levels of internode and leaf. OsCCX2 is localized to plasma membrane, and OsCCX2 is mainly expressed in xylem region of vascular tissues at the nodes. OsCCX2 might function as an efflux transporter, responsible for Cd loading into xylem vessels. Therefore, our finding revealed a novel Cd transporter involved in grain Cd accumulation, possibly via a Ca transport pathway in the nodes of rice.

水稻（Oryza sativa L.）籽粒中镉（Cd）过量积累会对粮食安全构成威胁。水稻节部的转运蛋白参与包括有毒元素在内的矿质元素向籽粒等不同组织的分配过程。然而，籽粒中镉积累的具体机制在很大程度上仍未被阐明。本研究报道了一个在节部表达的转运蛋白基因OsCCX2，其属于假定的阳离子/钙（Ca）交换体，可介导水稻籽粒中的镉积累。敲除OsCCX2会导致水稻籽粒中的镉含量显著降低。进一步研究表明，该基因的功能缺失会降低镉从根向地上部的转运比率；此外，镉在不同节间和叶片中的分布也受到干扰。OsCCX2定位于质膜，且主要在水稻节部维管组织的木质部区域表达。OsCCX2可能作为外排转运蛋白发挥功能，负责将镉装载进入木质部导管。因此，本研究发现了一个参与水稻籽粒镉积累的新型镉转运蛋白，其可能通过水稻节部的钙转运通路发挥作用。