© 2007 The Author(s).
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RESEARCH PAPER |
Cloning and functional comparison of a high-affinity K+ transporter gene PhaHKT1 of salt-tolerant and salt-sensitive reed plants
1Asian Natural Environmental Science Center (ANESC), The University of Tokyo, 1-1-1 Midori-cho, Nishitokyo-shi, Tokyo 188-0002, Japan
2Alkali Soil Natural Environmental Science Center (ASNESC), Northeast Forestry University, Harbin 150040, PR China
* To whom correspondence should be addressed: E-mail: takano{at}anesc.u-tokyo.ac.jp
To understand the mechanisms of ion homeostasis in salt-tolerant and salt-sensitive plants, cDNAs for a high-affinity K+ transporter PhaHKT1 were isolated from salt-sensitive (Utsunomiya) and salt-tolerant (Nanpi, Enchi) reed plants. A cDNA of Utsunomiya (PhaHKT1-u) contained two insertions in the region corresponding to the first and second introns of the PhaHKT1 gene, which resulted in a sequence 141 amino acid residues shorter than that of Nanpi. Expression of PhaHKT1 mRNA was detected in the roots of Nanpi and Enchi plants under K+ starvation conditions and also under Na+ treatment conditions, whereas it was only slightly detected in the roots of Utsunomiya plants under each of these conditions. In the upper parts, PhaHKT1 expression was detected in the Utsunomiya plants, and two signals were obtained in the Nanpi and Enchi plants under all and K+ starvation conditions, respectively. Yeasts expressing the PhaHKT1 of Nanpi (PhaHKT1-n) or the PhaHKT1 of Enchi (PhaHKT1-e) grew better in the presence of NaCl than yeast expressing PhaHKT1-u. Furthermore, yeast expressing a chimeric cDNA containing the 5' region of the Utsunomiya gene and the 3' region of the Nanpi gene had partial salt tolerance, and yeast expressing a chimeric cDNA containing the 5' region of the Nanpi gene and the 3' region of the Utsunomiya gene had a reduced ability to take up ions. These results suggest that PhaHKT1 plays an important role in the acquisition of K+ and maintenance of ion balance under saline conditions.
Key words: HKT, PhaHKT1, potassium transporter, reed plants, salt stress, salt tolerance, sodium influx
Received 20 September 2007; Revised 29 October 2007 Accepted 31 October 2007
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