Yoshimoto Naoko, Takahashi Hideki, Smith Frank W, Yamaya Tomoyuki, Saito Kazuki
Department of Molecular Biology and Biotechnology, Graduate School of Pharmaceutical Sciences, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522, Japan.
Plant J. 2002 Feb;29(4):465-73. doi: 10.1046/j.0960-7412.2001.01231.x.
Sulfate transporters present at the root surface facilitate uptake of sulfate from the environment. Here we report that uptake of sulfate at the outermost cell layers of Arabidopsis root is associated with the functions of highly and low-inducible sulfate transporters, Sultr1;1 and Sultr1;2, respectively. We have previously reported that Sultr1;1 is a high-affinity sulfate transporter expressed in root hairs, epidermal and cortical cells of Arabidopsis roots, and its expression is strongly upregulated in plants deprived of external sulfate. A novel sulfate transporter gene, Sultr1;2, identified on the BAC clone F28K19 of Arabidopsis, encoded a polypeptide of 653 amino acids that is 72.6% identical to Sultr1;1 and was able to restore sulfate uptake capacity of a yeast mutant lacking sulfate transporter genes (K(m) for sulfate = 6.9 +/- 1.0 microm). Transgenic Arabidopsis plants expressing the fusion gene construct of the Sultr1;2 promoter and green fluorescent protein (GFP) showed specific localization of GFP in the root hairs, epidermal and cortical cells of roots, and in the guard cells of leaves, suggesting that Sultr1;2 may co-localize with Sultr1;1 in the same cell layers at the root surface. Sultr1;1 mRNA was abundantly expressed under low-sulfur conditions (50-100 microm sulfate), whereas Sultr1;2 mRNA accumulated constitutively at high levels under a wide range of sulfur conditions (50-1500 microm sulfate), indicating that Sultr1;2 is less responsive to changes in sulfur conditions. Addition of selenate to the medium increased the level of Sultr1;1 mRNA in parallel with a decrease in the internal sulfate pool in roots. The level of Sultr1;2 mRNA was not influenced under these conditions. Antisense plants of Sultr1;1 showed reduced accumulation of sulfate in roots, particularly in plants treated with selenate, suggesting that the inducible transporter Sultr1;1 contributes to the uptake of sulfate under stressed conditions.
根表面存在的硫酸盐转运蛋白促进了植物从环境中吸收硫酸盐。在此我们报告，拟南芥根最外层细胞层对硫酸盐的吸收分别与高诱导型和低诱导型硫酸盐转运蛋白Sultr1;1和Sultr1;2的功能相关。我们之前报道过，Sultr1;1是一种在拟南芥根毛、表皮和皮层细胞中表达的高亲和力硫酸盐转运蛋白，在缺乏外部硫酸盐的植物中其表达会强烈上调。在拟南芥的BAC克隆F28K19上鉴定出一个新的硫酸盐转运蛋白基因Sultr1;2，它编码一个由653个氨基酸组成的多肽，与Sultr1;1有72.6%的同一性，并且能够恢复缺乏硫酸盐转运蛋白基因的酵母突变体的硫酸盐吸收能力（硫酸盐的K(m)=6.9±1.0微摩尔）。表达Sultr1;2启动子与绿色荧光蛋白（GFP）融合基因构建体的转基因拟南芥植株显示，GFP在根毛、根的表皮和皮层细胞以及叶的保卫细胞中有特异性定位，这表明Sultr1;2可能与Sultr1;1在根表面的同一细胞层中共定位。Sultr1;1 mRNA在低硫条件下（50 - 100微摩尔硫酸盐）大量表达，而Sultr1;2 mRNA在广泛的硫条件下（50 - 1500微摩尔硫酸盐）持续高水平积累，这表明Sultr1;2对硫条件变化的反应较小。向培养基中添加硒酸盐会使Sultr1;1 mRNA水平升高，同时根中内部硫酸盐库减少。在这些条件下，Sultr1;2 mRNA水平不受影响。Sultr1;1的反义植株根中硫酸盐积累减少，特别是在用硒酸盐处理的植株中，这表明诱导型转运蛋白Sultr1;1在胁迫条件下有助于硫酸盐的吸收。
