The wheat sodium transporters TmHKT1;5‐A and TaHKT1;5‐D are encoded by genes underlying the major shoot Na⁺ exclusion loci Nax2 and Kna1 from Triticum monococcum (Tm) and Triticum aestivum (Ta), respectively. In contrast to HKT2 transporters that have been shown to exhibit high affinity K⁺‐dependent Na⁺ transport, HKT1 proteins have, with one exception, only been shown to catalyze low affinity Na⁺ transport and no K⁺ transport. Here, using heterologous expression in Xenopus laevis oocytes we uncover a novel property of HKT1 proteins, that both TmHKT1;5‐A and TaHKT1;5‐D encode dual (high and low) affinity Na⁺‐transporters with the high‐affinity component being abolished when external K⁺ is in excess of external Na⁺. Three‐dimensional structural modeling suggested that, compared to Na⁺, K⁺ is bound more tightly in the selectivity filter region by means of additional van der Waals forces, which is likely to explain the K⁺ block at the molecular level. The low‐affinity component for Na⁺ transport of TmHKT1;5‐A had a lower K_m than that of TaHKT1;5‐D and was less sensitive to external K⁺. We propose that these properties contribute towards the improvements in shoot Na⁺‐exclusion and crop plant salt tolerance following the introgression of TmHKT1;5‐A into diverse wheat backgrounds.

中文翻译：

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小麦 HKT1;5 的高亲和力 Na+ 转运被 K+ 阻断


小麦钠转运蛋白 TmHKT1;5-A 和 TaHKT1;5-D 分别由来自小麦(Tm) 和普通小麦(Ta) 的主要芽 Na ⁺排除位点Nax2和Kna1的基因编码。与已显示出高亲和力 K ⁺依赖性 Na ⁺转运的 HKT2 转运蛋白相比，HKT1 蛋白（除一个例外）仅显示出催化低亲和力 Na ⁺转运而无 K ⁺转运。在这里，利用非洲爪蟾卵母细胞中的异源表达，我们发现了 HKT1 蛋白的一个新特性，即 TmHKT1;5-A 和 TaHKT1;5-D 编码双（高和低）亲和力 Na ⁺转运蛋白，其中高亲和力成分是当外部K ⁺超过外部Na ⁺时取消。三维结构模型表明，与Na ⁺相比，K ⁺通过额外的范德华力在选择性过滤区域中结合得更紧密，这可能在分子水平上解释K ⁺嵌段。 TmHKT1;5-A 的 Na ⁺转运低亲和力组分的 K _m低于 TaHKT1;5-D 的 K m ，并且对外部 K ⁺不太敏感。我们认为，在 TmHKT1;5-A 渗入不同的小麦背景后，这些特性有助于改善芽 Na ⁺排除和作物植物的耐盐性。