Institute of Plant Science and Resources, Okayama University, Chuo 2-20-1, Kurashiki 710-0046, Japan.
Plant Cell. 2023 May 29;35(6):2232-2250. doi: 10.1093/plcell/koad073.
Silicon (Si) is important for stable and high yields in rice (Oryza sativa), a typical Si hyperaccumulator. The high Si accumulation is achieved by the cooperation of 2 Si transporters, LOW SILICON 1 (OsLsi1) and OsLsi2, which are polarly localized in cells of the root exodermis and endodermis. However, the mechanism underlying their polar localization is unknown. Here, we identified amino acid residues critical for the polar localization of OsLsi1. Deletion of both N- and C-terminal regions resulted in the loss of its polar localization. Furthermore, the deletion of the C-terminus inhibited its trafficking from the endoplasmic reticulum to the plasma membrane. Detailed site-directed mutagenesis analysis showed that Ile18 at the N-terminal region and Ile285 at the C-terminal region were essential for the polar localization of OsLsi1. Moreover, a cluster of positively charged residues at the C-terminal region is also required for polar localization. Phosphorylation and Lys modifications of OsLsi1 are unlikely to be involved in its polar localization. Finally, we showed that the polar localization of OsLsi1 is required for the efficient uptake of Si. Our study not only identified critical residues required for the polar localization of OsLsi1, but also provided experimental evidence for the importance of transporter polarity for efficient nutrient uptake.
硅（Si）对于水稻（Oryza sativa）的稳定和高产很重要，水稻是一种典型的 Si 超积累植物。高 Si 积累是通过 2 种 Si 转运蛋白 LOW SILICON 1（OsLsi1）和 OsLsi2 的合作实现的，这两种蛋白在根表皮和内皮层细胞中呈极性定位。然而，其极性定位的机制尚不清楚。在这里，我们鉴定了对 OsLsi1 极性定位至关重要的氨基酸残基。N 端和 C 端区域的缺失导致其极性定位丧失。此外，C 端缺失抑制了其从内质网向质膜的运输。详细的定点突变分析表明，N 端的 Ile18 和 C 端的 Ile285 对 OsLsi1 的极性定位是必需的。此外，C 端带正电荷的残基簇也需要 OsLsi1 的极性定位。OsLsi1 的磷酸化和赖氨酸修饰不太可能参与其极性定位。最后，我们表明 OsLsi1 的极性定位对于 Si 的有效吸收是必需的。我们的研究不仅鉴定了 OsLsi1 极性定位所需的关键残基，还为转运蛋白极性对于有效养分吸收的重要性提供了实验证据。
