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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Rice Shaker Potassium Channel OsKAT1 Confers Tolerance to Salinity Stress on Yeast and Rice Cells^1,[OA]

Division of Plant Sciences, National Institute of Agrobiological Sciences, Tsukuba 305–8602, Japan (T.O., A.K., A.F., Y.T.); and Environmental Biofunction Division, National Institute for Agro-Environmental Sciences, Tsukuba 305–8604, Japan (H.K.K.)

We screened a rice (Oryza sativa L. ‘Nipponbare’) full-length cDNA expression library through functional complementation in yeast (Saccharomyces cerevisiae) to find novel cation transporters involved in salt tolerance. We found that expression of a cDNA clone, encoding the rice homolog of Shaker family K⁺ channel KAT1 (OsKAT1), suppressed the salt-sensitive phenotype of yeast strain G19 (ena1–4), which lacks a major component of Na⁺ efflux. It also suppressed a K⁺-transport-defective phenotype of yeast strain CY162 (trk1trk2), suggesting the enhancement of K⁺ uptake by OsKAT1. By the expression of OsKAT1, the K⁺ contents of salt-stressed G19 cells increased during the exponential growth phase. At the linear phase, however, OsKAT1-expressing G19 cells accumulated less Na⁺ than nonexpressing cells, but almost the same K⁺. The cellular Na⁺ to K⁺ ratio of OsKAT1-expressing G19 cells remained lower than nonexpressing cells under saline conditions. Rice cells overexpressing OsKAT1 also showed enhanced salt tolerance and increased cellular K⁺ content. These functions of OsKAT1 are likely to be common among Shaker K⁺ channels because OsAKT1 and Arabidopsis (Arabidopsis thaliana) KAT1 were able to complement the salt-sensitive phenotype of G19 as well as OsKAT1. The expression of OsKAT1 was restricted to internodes and rachides of wild-type rice, whereas other Shaker family genes were expressed in various organs. These results suggest that OsKAT1 is involved in salt tolerance of rice in cooperation with other K⁺ channels by participating in maintenance of cytosolic cation homeostasis during salt stress and thus protects cells from Na⁺.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Yoshiyuki Tanaka (tanakayo{at}affrc.go.jp).

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www.plantphysiol.org/cgi/doi/10.1104/pp.107.101154

^* Corresponding author; e-mail tanakayo{at}affrc.go.jp; fax 81–29–838–8347.

Received April 17, 2007; accepted June 18, 2007; published June 22, 2007.

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