HKT1;5 loci/alleles are important determinants of crop salinity tolerance. HKT1;5s encode plasmalemma-localized Na+-transporters, retrieving xylem Na+ into xylem parenchyma cells, reducing shoot Na+ accumulation. Allelic variation in rice OsHKT1;5 sequence in specific landraces (Nona Bokra OsHKT1;5-NB/Nipponbare OsHKT1;5-Ni) correlates with variation in salt tolerance. Oryza coarctata, a halophytic wild rice, grows in fluctuating salinity at the seawater-estuarine interface in Indian and Bangladeshi coastal regions. The distinct transport characteristics of the shoots and roots expressing O. coarctata OcHKT1;5 transporter, are reported vis-à-vis OsHKT1;5-Ni. Yeast sodium extrusion-deficient cells expressing OcHKT1;5 are sensitive to increasing Na+ (10-100 mM). Electrophysiological measurements in Xenopus oocytes expressing O. coarctata or rice HKT1;5 transporters indicates that OcHKT1;5, like OsHKT1;5-Ni is a Na+-selective transporter, but displays 16-fold lower affinity for Na+ and 3.5-fold higher maximal conductance than OsHKT1;5-Ni. For Na+ concentrations greater than 10 mM, OcHKT1;5 conductance is higher than that of OsHKT1;5-Ni, indicating potential of OcHKT1;5 for increasing domesticated rice salt tolerance. Homology modeling/ simulation suggests that four key amino acid changes in OcHKT1;5 (in loops on the extracellular side; E239K, G207R, G214R, L363V), account for its lower affinity and higher Na+ conductance vis-à-vis OsHKT1;5-Ni. Of these, E239K in OcHKT1;5, confers lower affinity for Na+ transport, as evidenced by Na+ transport assays of reciprocal site directed mutants for both transporters (OcHKT1;5- K239E, OsHKT1;5-Ni- E270K) in Xenopus oocytes. Both transporters have analogous roles in xylem sap desalinization and differences in Na+ transport affinity/ conductance between the transporters is attributable to differences in xylem sap Na+ concentrations in both species.

中文翻译：

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同源性模型鉴定了关键的氨基酸残基，这些残基赋予了Oryza coarctata Roxb更高的OcHKT1; 5 Na +转运能力。

HKT1; 5基因座/等位基因是作物耐盐性的重要决定因素。HKT1; 5s编码质膜定位的Na +转运蛋白，将木质部Na +提取到木质部薄壁细胞中，减少芽Na +的积累。特定地方品种（Nona Bokra OsHKT1; 5-NB / Nipponbare OsHKT1; 5-Ni）中水稻OsHKT1; 5序列的等位基因变异与耐盐性变异相关。Oryza coarctata是一种盐生植物性野生稻，在印度和孟加拉国沿海地区的海水-河口界面处，盐分的波动性使其生长。据报道，相对于OsHKT1; 5-Ni，表达O. coarctata OcHKT1; 5转运蛋白的芽和根的独特转运特性。表达OcHKT1; 5的酵母钠缺乏缺陷细胞对增加的Na +（10-100 mM）敏感。表达O的非洲爪蟾卵母细胞的电生理测量。coarctata或水稻HKT1; 5转运蛋白表明OcHKT1; 5像OsHKT1; 5-Ni是Na +选择性转运蛋白，但与OsHKT1; 5-Ni相比，对Na +的亲和力低16倍，最大电导率高3.5倍。对于Na +浓度大于10 mM的情况，OcHKT1; 5的电导率高于OsHKT1; 5-Ni，表明OcHKT1; 5具有提高驯化大米耐盐性的潜力。同源性建模/模拟表明，OcHKT1; 5的四个关键氨基酸变化（在细胞外侧成环； E239K，G207R，G214R，L363V）说明了其相对于OsHKT1; 5-具有较低的亲和力和较高的Na +电导率； 5-你。其中，OcHKT1; 5中的E239K赋予较低的Na +转运亲和力，非洲爪蟾卵母细胞中两个转运蛋白（OcHKT1; 5-K239E，OsHKT1; 5-Ni-E270K）的双向定点突变体的Na +转运测定证明了这一点。