Almeida PM , de Boer GJ , de Boer AH .

	Figure 1. Tomato accessions show SNPs close to the S at the filter position of the first pore domain, but not in the nucleotides coding the S residue. (A) Solanum HKT1;2 melting curve derivative plots from 93 tomato accessions showing the two different SNP's identified close to the 1st pore domain. (B) Nucleotide sequences of the HKT1;2 gene of different Solanum accessions show that both SNPs (red letters) situate close to, but do not coincide with the S70 residue of the first pore domain (green letters). Black colored letters represent conserved nucleotides.
	Figure 2. Transport activity of AtHKT1;1, AtHKT1;1-S68G, SlHKT1;2 and SlHKT1;2-S70G constructs expressed in Xenopus laevis oocytes. Oocytes were injected with AtHKT1;1 and SlHKT1;2 and the indicated mutated transporters. (A,E,I,M) Currents recorded at three Na+ concentrations (1, 3, and 10 mM) with 1 mM K+ as background; (B,F,J,N) Currents recorded at three K+ concentrations (1, 3, and 10 mM) with 1 mM Na+ as background; (C,G,K,O) Reversal potential shifts as a function of ion concentration. Only transporters where the S of the 1st pore domain was mutated to a G were permeable to K+ as indicated by the large positive shifts in the reversal potential with increasing concentrations of K+ in the bath; (D,H,L,P) Absolute currents as a function of ion concentration. Transporters where the S of the 1st pore domain was mutated to a G showed an increase in current with increasing K+ concentration in the bath. Data are means ± SE (n = 3, experiments done with at least two different oocyte batches).
	Figure 3. Detection of GUS activity in the vascular system of transgenic Arabidopsis thaliana plants. Arabidopsis plants expressed the GUS gene under the control of the AtHKT1;1 promoter were grown. Strong blue GUS staining was detected in the vicinity of the xylem and phloem in leaves. Arrows point to the xylem vessels. Biological replicates, n = 3; plantlets, n = 7.
	Figure 4. Presence of 100 mM NaCl in the irrigation water during 2 weeks significantly reduced the fresh weight of transformed, WT and athkt1;1 (N6531) Arabidopsis plants in comparison to control plants irrigated with water not supplemented with NaCl. Different inhibitions on the fresh weight production are observed amongst different transformed plant lines. Arabidopsis WT and athkt1;1 plants were used as positive and negative controls, respectively. Treatment: p < 0.05; plant lines: p < 0.05; treatment*plant lines (n.s.); Two-Way ANOVA. Values indicate the means ± SE of three to seven biological replicates.
	Figure 5. Differences in ion accumulation between all plants analyzed. Na+ (A) and K+ (B) accumulation and Na+/K+ (C) ratio in the shoot of WT, athkt1;1 mutant (N6531) and transgenic lines expressing different HKT1 genes. Na+/K+ ratio was normalized for WT. The effect of the mutation in the AtHKT1;1 gene is very clear, showing a strong increase in shoot Na+ accompanied by a decrease in K+, which resulted in a very strong increase in the Na+/K+ ratio. Both lines expressing AtHKT1;1::AtHKT1;1 or AtHKT1;1::SlHKT1;2 were able to reduce the accumulation of Na+ and increase the accumulation of K+ in comparison to athkt1;1. Lines expressing AtHKT1;1::AtHKT1;1-S68G or AtHKT1;1::SlHKT1;2-S70G were not able to ameliorate the phenotype of the athkt1;1 plants. Different letters above bars indicate statistically significant differences. Values indicate the means ± SE of three to seven biological replicates.
	Figure 6. Model depicting the difference in K+-sensitivity of SlHKT1;2 from S. esculentum and AtHKT1;1 from Arabidopsis. When the K+-concentration in the xylem sap is high, Na+-uptake by the SlHKT1;2 transporter is reduced. As a result the amount of Na+ in the xylem stream reaching the shoot of tomato is, at least partially, controlled by SlHKT1;2, which in turn depends on the concentration of K+ present in the xylem sap. In Arabidopsis, Na+-uptake in the XPCs by the AtHKT1;1 transporter is not affected by high K+.

Ali, TsHKT1;2, a HKT1 homolog from the extremophile Arabidopsis relative Thellungiella salsuginea, shows K(+) specificity in the presence of NaCl. 2012, Pubmed

Ali, TsHKT1;2, a HKT1 homolog from the extremophile Arabidopsis relative Thellungiella salsuginea, shows K(+) specificity in the presence of NaCl. 2012, Pubmed
Almeida, Differences in shoot Na+ accumulation between two tomato species are due to differences in ion affinity of HKT1;2. 2014, Pubmed , Xenbase
Asins, Two closely linked tomato HKT coding genes are positional candidates for the major tomato QTL involved in Na+ /K+ homeostasis. 2013, Pubmed
Baek, Regulated AtHKT1 gene expression by a distal enhancer element and DNA methylation in the promoter plays an important role in salt tolerance. 2011, Pubmed
Baxter, A coastal cline in sodium accumulation in Arabidopsis thaliana is driven by natural variation of the sodium transporter AtHKT1;1. 2010, Pubmed
Berthomieu, Functional analysis of AtHKT1 in Arabidopsis shows that Na(+) recirculation by the phloem is crucial for salt tolerance. 2003, Pubmed , Xenbase
Byrt, HKT1;5-like cation transporters linked to Na+ exclusion loci in wheat, Nax2 and Kna1. 2007, Pubmed
Clough, Floral dip: a simplified method for Agrobacterium-mediated transformation of Arabidopsis thaliana. 1998, Pubmed
Cominelli, Transgenic crops coping with water scarcity. 2010, Pubmed
Cotsaftis, A two-staged model of Na+ exclusion in rice explained by 3D modeling of HKT transporters and alternative splicing. 2012, Pubmed
Davenport, Control of sodium transport in durum wheat. 2005, Pubmed
Diatloff, Site directed mutagenesis reduces the Na+ affinity of HKT1, an Na+ energized high affinity K+ transporter. 1998, Pubmed
Fairbairn, Characterisation of two distinct HKT1-like potassium transporters from Eucalyptus camaldulensis. 2000, Pubmed , Xenbase
Garciadeblás, Sodium transport and HKT transporters: the rice model. 2003, Pubmed
Gassman, Alkali cation selectivity of the wheat root high-affinity potassium transporter HKT1. 1996, Pubmed , Xenbase
Golldack, Characterization of a HKT-type transporter in rice as a general alkali cation transporter. 2002, Pubmed , Xenbase
Haro, HKT1 mediates sodium uniport in roots. Pitfalls in the expression of HKT1 in yeast. 2005, Pubmed
Horie, Rice OsHKT2;1 transporter mediates large Na+ influx component into K+-starved roots for growth. 2007, Pubmed
Horie, K+ transport by the OsHKT2;4 transporter from rice with atypical Na+ transport properties and competition in permeation of K+ over Mg2+ and Ca2+ ions. 2011, Pubmed , Xenbase
Horie, Two types of HKT transporters with different properties of Na+ and K+ transport in Oryza sativa. 2001, Pubmed , Xenbase
Huang, A sodium transporter (HKT7) is a candidate for Nax1, a gene for salt tolerance in durum wheat. 2006, Pubmed
Jabnoune, Diversity in expression patterns and functional properties in the rice HKT transporter family. 2009, Pubmed , Xenbase
James, Physiological characterization of two genes for Na+ exclusion in durum wheat, Nax1 and Nax2. 2006, Pubmed
Jefferson, GUS fusions: beta-glucuronidase as a sensitive and versatile gene fusion marker in higher plants. 1987, Pubmed
Jha, Variation in salinity tolerance and shoot sodium accumulation in Arabidopsis ecotypes linked to differences in the natural expression levels of transporters involved in sodium transport. 2010, Pubmed
Karimi, GATEWAY vectors for Agrobacterium-mediated plant transformation. 2002, Pubmed
Kato, Role of positively charged amino acids in the M2D transmembrane helix of Ktr/Trk/HKT type cation transporters. 2007, Pubmed , Xenbase
Lan, A rice high-affinity potassium transporter (HKT) conceals a calcium-permeable cation channel. 2010, Pubmed
Laurie, A role for HKT1 in sodium uptake by wheat roots. 2002, Pubmed
Liu, Characterization of two HKT1 homologues from Eucalyptus camaldulensis that display intrinsic osmosensing capability. 2001, Pubmed , Xenbase
Livak, Analysis of relative gene expression data using real-time quantitative PCR and the 2(-Delta Delta C(T)) Method. 2001, Pubmed
Mian, Over-expression of an Na+-and K+-permeable HKT transporter in barley improves salt tolerance. 2011, Pubmed , Xenbase
Munns, Mechanisms of salinity tolerance. 2008, Pubmed
Munns, Wheat grain yield on saline soils is improved by an ancestral Na⁺ transporter gene. 2012, Pubmed , Xenbase
Mäser, Glycine residues in potassium channel-like selectivity filters determine potassium selectivity in four-loop-per-subunit HKT transporters from plants. 2002, Pubmed , Xenbase
Møller, Shoot Na+ exclusion and increased salinity tolerance engineered by cell type-specific alteration of Na+ transport in Arabidopsis. 2009, Pubmed
Platten, Nomenclature for HKT transporters, key determinants of plant salinity tolerance. 2006, Pubmed
Plett, Improved salinity tolerance of rice through cell type-specific expression of AtHKT1;1. 2010, Pubmed
Ren, A rice quantitative trait locus for salt tolerance encodes a sodium transporter. 2005, Pubmed
Rodríguez-Navarro, Potassium transport in fungi and plants. 2000, Pubmed
Rubio, Genetic selection of mutations in the high affinity K+ transporter HKT1 that define functions of a loop site for reduced Na+ permeability and increased Na+ tolerance. 1999, Pubmed , Xenbase
Rubio, Sodium-driven potassium uptake by the plant potassium transporter HKT1 and mutations conferring salt tolerance. 1995, Pubmed , Xenbase
Rus, AtHKT1 facilitates Na+ homeostasis and K+ nutrition in planta. 2004, Pubmed
Rus, AtHKT1 is a salt tolerance determinant that controls Na(+) entry into plant roots. 2001, Pubmed
Rus, Unraveling salt tolerance in crops. 2005, Pubmed
Schachtman, Structure and transport mechanism of a high-affinity potassium uptake transporter from higher plants. 1994, Pubmed , Xenbase
Su, Expression of the cation transporter McHKT1 in a halophyte. 2003, Pubmed , Xenbase
Sunarpi, Enhanced salt tolerance mediated by AtHKT1 transporter-induced Na unloading from xylem vessels to xylem parenchyma cells. 2005, Pubmed
Takahashi, Cloning and functional comparison of a high-affinity K+ transporter gene PhaHKT1 of salt-tolerant and salt-sensitive reed plants. 2007, Pubmed
Tholema, Change to alanine of one out of four selectivity filter glycines in KtrB causes a two orders of magnitude decrease in the affinities for both K+ and Na+ of the Na+ dependent K+ uptake system KtrAB from Vibrio alginolyticus. 1999, Pubmed
Uozumi, The Arabidopsis HKT1 gene homolog mediates inward Na(+) currents in xenopus laevis oocytes and Na(+) uptake in Saccharomyces cerevisiae. 2000, Pubmed , Xenbase
Yao, Differential sodium and potassium transport selectivities of the rice OsHKT2;1 and OsHKT2;2 transporters in plant cells. 2010, Pubmed , Xenbase