Rice (Oryza sativa) provides >20% of the consumed calories in the human diet. However, rice is also a leading source of dietary cadmium (Cd) that seriously threatens human health. Deciphering the genetic network that underlies the grain-Cd accumulation will benefit the development of low-Cd rice and mitigate the effects of Cd accumulation in the rice grain. In this study, we identified a QTL gene, OsCS1, which is allelic to OsMTP11 and encodes a protein sequestering Cd in the leaf during vegetative growth and preventing Cd from being translocated to the grain after heading in rice. OsCS1 is predominantly expressed in leaf vascular parenchyma cells, where it binds to a vacuole-sorting receptor protein OsVSR2 and is translocated intracellularly from the trans-Golgi network to pre-vacuolar compartments and then to the vacuole. In this trafficking process, OsCS1 actively transports Cd into the endomembrane system and sequesters it in the vacuoles. There are natural variations in the promoter of OsCS1 between the indica and japonica rice subspecies. Duplication of a G-box-like motif in the promoter region of the superior allele of OsCS1 from indica rice enhances the binding of the transcription factor OsIRO2 to the OsCS1 promoter, thereby promoting OsCS1 expression. Introgression of this allele into commercial rice varieties could significantly lower grain-Cd levels compared to the inferior allele present in japonica rice. Collectively, our findings offer new insights into the genetic control of leaf-to-grain Cd translocation and provide a novel gene and its superior allele for the genetic improvement of low-Cd variety in rice.

中文翻译：

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金属耐受蛋白 OsMTP11 促进镉在叶片维管细胞液泡中的封存，以限制其转位到稻粒中


大米 （Oryza sativa） 提供人类饮食中消耗的卡路里的 >20%。然而，稻米也是严重威胁人类健康的膳食镉 （Cd） 的主要来源。破译籽粒-镉积累的遗传网络将有利于低镉稻的发育，并减轻稻谷中镉积累的影响。在这项研究中，我们鉴定了一个 QTL 基因 OsCS1，它与 OsMTP11 等位，编码一种蛋白质，在营养生长过程中将 Cd 隔离在叶片中，并防止 Cd 在水稻抽穗后转移到谷物中。OsCS1 主要在叶维管束薄壁细胞中表达，在那里它与液泡分选受体蛋白 OsVSR2 结合，并在细胞内从反式高尔基体网络转移到液泡前隔室，然后转移到液泡。在这个运输过程中，OsCS1 主动将 Cd 转运到内膜系统中并将其隔离在液泡中。籼稻和粳稻亚种之间的 OsCS1 启动子存在自然变异。在籼稻 OsCS1 上等位基因的启动子区复制 G 盒样基序可增强转录因子 OsIRO2 与 OsCS1 启动子的结合，从而促进 OsCS1 的表达。与粳稻中存在的劣质等位基因相比，该等位基因渗入商业水稻品种可以显著降低谷物 Cd 水平。总的来说，我们的研究结果为叶粒 Cd 易位的遗传控制提供了新的见解，并为水稻低 Cd 品种的遗传改良提供了新的基因及其优越等位基因。