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Published on August 1, 2008; 10.1104/pp.108.124248

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Received June 9, 2008
Accepted July 29, 2008

AtCHX13 is a Plasma Membrane K+ Transporter

Jian Zhao , Ning-Hui Cheng , Christy M. Motes , Elison B. Blancaflor , Miranda Moore , Naomi Gonzales , Senthilkumar Padmanaban , Heven Sze , John M. Ward , and Kendal D. Hirschi *

United States Department of Agriculture-Agricultural Research Service Children's Nutrition Research Center, Baylor College of Medicine, 1100 Bates Street, Houston, Texas 77030; Plant Biology Division, Samuel Roberts Noble Foundation, Inc, 2510 Sam Noble Parkway, Ardmore, OK 73401 Department of Cell Biology & Molecular Genetics, Bioscience Research Building, University of Maryland, College Park, MD 20742-5815, USA; Department Plant Biology, 250 Biological Sciences Center, 1445 Gortner Ave., University of Minnesota, St. Paul, MN 55108, USA; Vegetable and Fruit Improvement Center, Texas A&M University, College Station, Texas 77845

* Corresponding author; email: kendalh{at}bcm.tmc.edu.

Potassium homeostasis is essential for diverse cellular processes, though how various cation transporters collaborate to maintain a suitable K+ required for growth and development is poorly understood. The Arabidopsis thaliana genome contains numerous cation:proton antiporters (CHX) which may mediate K+ transport; however, the vast majority of these transporters remain uncharacterized. Here we show that AtCHX13 (At2g30240) has a role in K+ acquisition. AtCHX13 suppressed the sensitivity of yeast mutant cells defective in K+ uptake. Uptake experiments using 86Rb+ as a tracer for K+ demonstrated that AtCHX13 mediated high-affinity K+ uptake in yeast and in plant cells with a Km of 136 µM and 196 µM, respectively. Functional GFP-tagged versions localized to the plasma membrane of both yeast and plant. Seedlings of null chx13 mutants were sensitive to K+ deficiency conditions, whereas over expression of AtCHX13 reduced the sensitivity to K+ deficiency. Collectively, these results suggest that AtCHX13 mediates relatively high-affinity K+ uptake though the mode of transport is unclear at present. AtCHX13 expression is induced in roots during K+ deficient conditions. These results indicate that one role of AtCHX13 is to promote K+ uptake into plants when K+ is limiting in the environment.




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