Institute of Plant Science and Resources, Okayama University, Kurashiki 710-0046, Japan.
Plant Physiol. 2024 Jul 31;195(4):2683-2693. doi: 10.1093/plphys/kiae289.
Rice (Oryza sativa) as a staple food is a potential intake source of antimony (Sb), a toxic metalloid. However, how rice accumulates this element is still poorly understood. Here, we investigated tissue-specific deposition, speciation, and transport of Sb in rice. We found that Sb(III) is the preferential form of Sb uptake in rice, but most Sb accumulates in the roots, resulting in a very low root-to-shoot translocation (less than 2%). Analysis of Sb deposition with laser ablation-inductively coupled plasma-mass spectrometry showed that most Sb deposits at the root exodermis. Furthermore, we found that Sb is mainly present as Sb(III) in the root cell sap after uptake. Further characterization showed that Sb(III) uptake is mediated by Low silicon rice 1 (Lsi1), a Si permeable transporter. Lsi1 showed transport activity for Sb(III) rather than Sb(V) in yeast (Saccharomyces cerevisiae). Knockout of Lsi1 resulted in a significant decrease in Sb accumulation in both roots and shoots. Sb concentration in the root cell sap of two independent lsi1 mutants decreased to less than 3% of that in wild-type rice, indicating that Lsi1 is a major transporter for Sb(III) uptake. Knockout of Lsi1 also enhanced rice tolerance to Sb toxicity. However, knockout of Si efflux transporter genes, including Lsi2 and Lsi3, did not affect Sb accumulation. Taken together, our results showed that Sb(III) is taken up by Lsi1 localized at the root exodermis and is deposited at this cell layer due to lack of Sb efflux transporters in rice.
水稻（Oryza sativa）作为主食是摄入锑（Sb）这种有毒类金属元素的潜在来源。然而，水稻是如何积累这种元素的仍不清楚。在这里，我们研究了 Sb 在水稻中的组织特异性积累、形态和运输。我们发现 Sb(III)是水稻吸收 Sb 的主要形式，但大部分 Sb 积累在根部，导致根到茎的转运率非常低（低于 2%）。用激光烧蚀-电感耦合等离子体质谱法分析 Sb 沉积发现，大部分 Sb 沉积在根外表皮。此外，我们发现 Sb 吸收后主要以 Sb(III)的形式存在于根细胞液中。进一步的特征分析表明，Sb(III)的吸收是由低硅水稻 1（Lsi1）介导的，Lsi1 是一种 Si 通透转运蛋白。Lsi1 在酵母（Saccharomyces cerevisiae）中对 Sb(III)而非 Sb(V)具有转运活性。Lsi1 的敲除导致根部和地上部 Sb 积累量显著减少。两个独立的 lsi1 突变体的根细胞液中 Sb 浓度降低到野生型水稻的 3%以下，表明 Lsi1 是 Sb(III)吸收的主要转运蛋白。Lsi1 的敲除也增强了水稻对 Sb 毒性的耐受性。然而，Si 外排转运蛋白基因（包括 Lsi2 和 Lsi3）的敲除并不影响 Sb 积累。总之，我们的结果表明，Sb(III)被定位于根外表皮的 Lsi1 吸收，由于水稻中缺乏 Sb 外排转运蛋白，Sb 被沉积在这个细胞层。
