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

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.