Location: Children's Nutrition Research CenterTitle: AtCHX13 is a plasma membrane K+ transporter Author
Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/2008
Publication Date: 10/1/2008
Citation: Zhao, J., Cheng, N., 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+) element is an essential nutrient for plant (crop) growth and development. Plants utilize different types of K+ transporters to uptake and mobilize this mineral ion within and through cells. Improving plant (crop)'s capacity of tolerance to nutrient (K+)- deficient soil conditions is a growing challenge for agricultural production in both US and around world. There are many membrane transporters identified as K+ transporters. However, the detailed function of those metal-ion transporters is still largely unknown. This work has gained significant knowledge regarding one of novel potassium transporters, termed AtCHX13. Using biochemical and genetic analyses and cell biology approaches, we demonstrated that AtCHX13 was localized in the plasma membrane and could actively transport K+. Furthermore, this particular transporter gene was highly induced in roots when the K+ element was deficient, suggesting a critical role of this transporter in the uptake of potassium ion from soil. This study provides insights on characterization of this new group of K+ transporters in crops and the potential utility of genetically engineering to improve metal stress tolerance of crops.
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 microm, 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.