Two types of HKT transporters with different properties of Na+ and K+ transport in Oryza sativa
Two types of HKT transporters with different properties of Na+ and K+ transport in Oryza sativa
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DOI：
10.1046/j.1365-313x.2001.01077.x
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发表时间：
2001-07-01
期刊：
影响因子：
7.2
通讯作者：
Shinmyo, A
中科院分区：
文献类型：
--
作者：
Horie, T;Yoshida, K;Shinmyo, A
Na ~+、K ~+的动态平衡被认为是植物耐盐性的关键。为了更好地了解重要作物水稻（Oryza sativa L.）的Na ~+、K ~+动态平衡，从粳稻ev Nipponbare（Ni-OsHKT 1）中分离到与小麦HKT 1同源的编码K+-Na+同向转运体的cDNA。我们还从耐盐籼稻品种Pokkali中分离到两个与Ni-OsHKT 1同源的cDNA（Po-OsHKT 1，Po-OsHKT 2）。Ni-OsHKT 1与Po-OsHKT 1和Po-OsHKT 2的氨基酸同源性分别为100%和91%，与小麦HKT 1的氨基酸同源性为66-67%。低K+条件（小于3 mm）诱导所有三个OsHKT基因在根中的表达，但mRNA的积累被抑制的存在下，30 mM Na+。我们进一步表征了OsHKT 1和OsHKT 2的离子转运特性，使用在异源细胞、酵母和爪蟾卵母细胞中的表达系统。OsHKT 2能够完全拯救酵母中的K+摄取缺陷突变，而OsHKT 1不处于K+限制条件下。当OsHKT在Na+敏感酵母中表达时，OsHKT 1使细胞在高NaCl条件下比OsHKT 2更Na+敏感。电生理实验表明，外源性Na+使OsHKT 1的反转电位向去极化方向移动，而K+则无此作用。相反，对于OsHKT 2，在含有Na+和K+的混合溶液中，外部溶液中的Na+或K+使反转电位向去极化方向移动。这些结果表明，HKT的两种异构体，Na+转运蛋白（OsHKT 1）和Na+和K+耦合转运蛋白（OsHKT 2），可能在耐盐籼稻中协调发挥作用。
It is thought that Na+ and K+ homeostasis is crucial for salt-tolerance in plants, To better understand the Na+ and K+ homeostasis in important crop rice (Oryza sativa L.), a cDNA homologous to the wheat HKT1 encoding K+-Na+ symporter was isolated from japonica rice, ev Nipponbare (Ni-OsHKT1). We also isolated two cDNAs homologous to Ni-OsHKT1 from salt-tolerant indica rice, cv Pokkali (Po-OsHKT1, Po-OsHKT2). The predicted amino acid sequence of Ni-OsHKT1 shares 100% identity with Po-OsHKT1 and 91% identity with Po-OsHKT2, and they are 66-67% identical to wheat HKT1. Low-K+ conditions (less than 3 mm) induced the expression of all three OsHKT genes in roots, but mRNA accumulation was inhibited by the presence of 30 mM Na+. We further characterized the ion-transport properties of OsHKT1 and OsHKT2 using an expression system in the heterologous cells, yeast and Xenopus oocytes. OsHKT2 was capable of completely rescuing a K+-uptake 'deficiency mutation in yeast, whereas OsHKT1 was not under K+-limiting conditions. When OsHKTs were expressed in Na+-sensitive yeast, OsHKT1 rendered the cells more Na+-sensitive than did OsHKT2 in high NaCl conditions. The electrophysiological experiments for OsHKT1 expressed in Xenopus oocytes revealed that external Na+, but not K+, shifted the reversal potential toward depolarization. In contrast, for OsHKT2 either Na+ or K+ in the external solution shifted the reversal potential toward depolarization under the mixed Na+ and K+ containing solutions. These results suggest that two isoforms of HKT transporters, a Na+ transporter (OsHKT1) and a Na+- and K+-coupled transporter (OsHKT2), may act harmoniously in the salt tolerant indica rice.