Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2008
Publication Date: 10/1/2008
Publication URL: http:////www.plantphysiol.org/cgi/reprint/148/2/796
Citation: Zhao, J., Cheng, N-H., Motes, C.M., Blancaflor, E.B., Moore, M., Gonzales, N., Padmanaban, S., Sze, H., Ward, J.M., Hirschi, K.D. 2008. AtCHX13 is a plasma membrane K(+) transporter. Plant Physiology. 148(2):796-807. Interpretive Summary: Potassium (K+) plays an essential role in plant growth and development and in the nutritional status of plants. The movement of K(+) in plants is controlled by a large number of transporters that traffic this nutrient into cells. Here we identified a new type of transporter that can move K(+) inside of plant cells. We characterized the mechanism of K(+) transport and showed that plants expressing high levels of this transporter contained more K(+) than controls. In the future this transporter may be used to increase the nutritional qualities of foods.
Technical Abstract: Potassium (K+) homeostasis is essential for diverse cellular processes, although how various cation transporters collaborate to maintain a suitable K(+) required for growth and development is poorly understood. The Arabidopsis ("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 ("Saccharomyces cerevisiae") mutant cells defective in K(+) uptake. Uptake experiments using (86)Rb(+) as a tracer for K(+) demonstrated that AtCHX13 mediated high-affinity K(+) uptake in yeast and in plant cells with a K[m] of 136 and 196 micron, respectively. Functional green fluorescent protein-tagged versions localized to the plasma membrane of both yeast and plant. Seedlings of null "chx13" mutants were sensitive to K(+) deficiency conditions, whereas overexpression of "AtCHX13" reduced the sensitivity to K(+) deficiency. Collectively, these results suggest that AtCHX13 mediates relatively high-affinity K(+) uptake, although 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.