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Cloning of a high-affinity K+ transporter gene PutHKT2;1 from Puccinellia tenuiflora and its functional comparison with OsHKT2;1 from rice in yeast and Arabidopsis.

Ardie SW, Xie L, Takahashi R, Liu S, Takano T - J. Exp. Bot. (2009)

Bottom Line: Arabidopsis over-expressing PutHKT2;1 showed increased sensitivities to Na+, K+, and Li+, while Arabidopsis over-expressing OsHKT2;1 from rice (Oryza sativa) showed increased sensitivity only to Na+.In contrast to OsHKT2;1, which functions in Na+-uptake at low external K+ concentrations, PutHKT2;1 functions in Na+-uptake at higher external K+ concentrations.These results show that the modes of action of PutHKT2;1 in transgenic yeast and Arabidopsis differ from the mode of action of the closely related OsHKT2;1 transporter.

View Article: PubMed Central - PubMed

Affiliation: Asian Natural Environmental Science Center (ANESC), The University of Tokyo, 1-1-1 Midori-cho, Nishitokyo-shi, Tokyo 188-0002, Japan.

ABSTRACT
A high-affinity K+ transporter PutHKT2;1 cDNA was isolated from the salt-tolerant plant Puccinellia tenuiflora. Expression of PutHKT2;1 was induced by both 300 mM NaCl and K+-starvation stress in roots, but only slightly regulated by those stresses in shoots. PutHKT2;1 transcript levels in 300 mM NaCl were doubled by the depletion of potassium. Yeast transformed with PutHKT2;1, like those transformed with PhaHKT2;1 from salt-tolerant reed plants (Phragmites australis), (i) were able to take up K+ in low K+ concentration medium or in the presence of NaCl, and (ii) were permeable to Na+. This suggests that PutHKT2;1 has a high affinity K+-Na+ symport function in yeast. Arabidopsis over-expressing PutHKT2;1 showed increased sensitivities to Na+, K+, and Li+, while Arabidopsis over-expressing OsHKT2;1 from rice (Oryza sativa) showed increased sensitivity only to Na+. In contrast to OsHKT2;1, which functions in Na+-uptake at low external K+ concentrations, PutHKT2;1 functions in Na+-uptake at higher external K+ concentrations. These results show that the modes of action of PutHKT2;1 in transgenic yeast and Arabidopsis differ from the mode of action of the closely related OsHKT2;1 transporter.

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Potassium-dependent Na-sensitivity of PutHKT2;1 and OsHKT2;1 over-expression lines. (A) Seven-day-old WT and transgenic seedlings grown on MS were transferred to minimal-medium supplemented with 1.75 mM or 0.1 mM KCl and 50 mM NaCl. (B) Shoot phenotype of seedlings grown in (A). Bar in each picture indicates 1 cm. (C) Root-lengths of WT and transgenic seedlings after the indicated treatments. Results are expressed as means ±SE (n=5).
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fig9: Potassium-dependent Na-sensitivity of PutHKT2;1 and OsHKT2;1 over-expression lines. (A) Seven-day-old WT and transgenic seedlings grown on MS were transferred to minimal-medium supplemented with 1.75 mM or 0.1 mM KCl and 50 mM NaCl. (B) Shoot phenotype of seedlings grown in (A). Bar in each picture indicates 1 cm. (C) Root-lengths of WT and transgenic seedlings after the indicated treatments. Results are expressed as means ±SE (n=5).

Mentions: OsHKT2;1 has been reported to mediate Na+ uptake into K+-starved roots in vivo (Horie et al., 2007). Therefore, WT and transgenic seedlings were subjected to various external K+ concentrations in the presence of 50 mM NaCl to determine the K+-dependency of PutHKT2;1. As expected, the root growth and shoot phenotype of OsHKT2;1-expressing seedlings were more adversely affected as the external K+ concentration decreased (Fig. 9), confirming that low external K+ concentration induces OsHKT2;1-mediated Na+-uptake. By contrast, the root growth and shoot phenotype of PutHKT2;1-expressing seedlings were more adversely affected as the external K+ concentration increased. The root growth and shoot phenotype of PutHKT2;1-expressing seedlings were indistinguishable from those of the WT in the presence of 50 mM NaCl and 0.1 mM KCl, indicating that PutHKT2;1 mediates Na+ uptake in the higher external K+ concentration range. Furthermore, external Ca2+ addition could rescue the Na-sensitivity of the WT, but Na+-sensitivities of PutHKT2;1- and OsHKT2;1-expressing seedlings were not affected by increasing the Ca2+ concentration in the medium from 0 mM to 3 mM (Fig. 10). In the lines expressing PutHKT2;1, Ca2+ was able to rescue the effects of Na+ stress slightly but only at 10 mM [CaExt2+]. Increasing [CaExt2+] from 0 mM to 10 mM increased the root length of PutHKT2;1-expressing seedlings 2–3-fold.


Cloning of a high-affinity K+ transporter gene PutHKT2;1 from Puccinellia tenuiflora and its functional comparison with OsHKT2;1 from rice in yeast and Arabidopsis.

Ardie SW, Xie L, Takahashi R, Liu S, Takano T - J. Exp. Bot. (2009)

Potassium-dependent Na-sensitivity of PutHKT2;1 and OsHKT2;1 over-expression lines. (A) Seven-day-old WT and transgenic seedlings grown on MS were transferred to minimal-medium supplemented with 1.75 mM or 0.1 mM KCl and 50 mM NaCl. (B) Shoot phenotype of seedlings grown in (A). Bar in each picture indicates 1 cm. (C) Root-lengths of WT and transgenic seedlings after the indicated treatments. Results are expressed as means ±SE (n=5).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2724696&req=5

fig9: Potassium-dependent Na-sensitivity of PutHKT2;1 and OsHKT2;1 over-expression lines. (A) Seven-day-old WT and transgenic seedlings grown on MS were transferred to minimal-medium supplemented with 1.75 mM or 0.1 mM KCl and 50 mM NaCl. (B) Shoot phenotype of seedlings grown in (A). Bar in each picture indicates 1 cm. (C) Root-lengths of WT and transgenic seedlings after the indicated treatments. Results are expressed as means ±SE (n=5).
Mentions: OsHKT2;1 has been reported to mediate Na+ uptake into K+-starved roots in vivo (Horie et al., 2007). Therefore, WT and transgenic seedlings were subjected to various external K+ concentrations in the presence of 50 mM NaCl to determine the K+-dependency of PutHKT2;1. As expected, the root growth and shoot phenotype of OsHKT2;1-expressing seedlings were more adversely affected as the external K+ concentration decreased (Fig. 9), confirming that low external K+ concentration induces OsHKT2;1-mediated Na+-uptake. By contrast, the root growth and shoot phenotype of PutHKT2;1-expressing seedlings were more adversely affected as the external K+ concentration increased. The root growth and shoot phenotype of PutHKT2;1-expressing seedlings were indistinguishable from those of the WT in the presence of 50 mM NaCl and 0.1 mM KCl, indicating that PutHKT2;1 mediates Na+ uptake in the higher external K+ concentration range. Furthermore, external Ca2+ addition could rescue the Na-sensitivity of the WT, but Na+-sensitivities of PutHKT2;1- and OsHKT2;1-expressing seedlings were not affected by increasing the Ca2+ concentration in the medium from 0 mM to 3 mM (Fig. 10). In the lines expressing PutHKT2;1, Ca2+ was able to rescue the effects of Na+ stress slightly but only at 10 mM [CaExt2+]. Increasing [CaExt2+] from 0 mM to 10 mM increased the root length of PutHKT2;1-expressing seedlings 2–3-fold.

Bottom Line: Arabidopsis over-expressing PutHKT2;1 showed increased sensitivities to Na+, K+, and Li+, while Arabidopsis over-expressing OsHKT2;1 from rice (Oryza sativa) showed increased sensitivity only to Na+.In contrast to OsHKT2;1, which functions in Na+-uptake at low external K+ concentrations, PutHKT2;1 functions in Na+-uptake at higher external K+ concentrations.These results show that the modes of action of PutHKT2;1 in transgenic yeast and Arabidopsis differ from the mode of action of the closely related OsHKT2;1 transporter.

View Article: PubMed Central - PubMed

Affiliation: Asian Natural Environmental Science Center (ANESC), The University of Tokyo, 1-1-1 Midori-cho, Nishitokyo-shi, Tokyo 188-0002, Japan.

ABSTRACT
A high-affinity K+ transporter PutHKT2;1 cDNA was isolated from the salt-tolerant plant Puccinellia tenuiflora. Expression of PutHKT2;1 was induced by both 300 mM NaCl and K+-starvation stress in roots, but only slightly regulated by those stresses in shoots. PutHKT2;1 transcript levels in 300 mM NaCl were doubled by the depletion of potassium. Yeast transformed with PutHKT2;1, like those transformed with PhaHKT2;1 from salt-tolerant reed plants (Phragmites australis), (i) were able to take up K+ in low K+ concentration medium or in the presence of NaCl, and (ii) were permeable to Na+. This suggests that PutHKT2;1 has a high affinity K+-Na+ symport function in yeast. Arabidopsis over-expressing PutHKT2;1 showed increased sensitivities to Na+, K+, and Li+, while Arabidopsis over-expressing OsHKT2;1 from rice (Oryza sativa) showed increased sensitivity only to Na+. In contrast to OsHKT2;1, which functions in Na+-uptake at low external K+ concentrations, PutHKT2;1 functions in Na+-uptake at higher external K+ concentrations. These results show that the modes of action of PutHKT2;1 in transgenic yeast and Arabidopsis differ from the mode of action of the closely related OsHKT2;1 transporter.

Show MeSH
Related in: MedlinePlus