Molecular and functional characterization of a novel low-affinity cation transporter (LCT1) in higher plants

Authors

Daniel P. Schachtman, University of Nebraska-LincolnFollow
Raman Kumar, University of Adelaide
Julian I. Schroeder, University of California at San Diego
Ellen L. Marsh, University of AdelaideFollow

Document Type

Article

Date of this Version

1997

Citation

Proc. Natl. Acad. Sci. USA Vol. 94, pp. 11079–11084, September 1997

Abstract

The transport of cations across membranes in higher plants plays an essential role in many physiological processes including mineral nutrition, cell expansion, and the transduction of environmental signals. In higher plants the coordinated expression of transport mechanisms is essential for specialized cellular processes and for adaptation to variable environmental conditions. To understand the molecular basis of cation transport in plant roots, a Triticum aestivum cDNA library was used to complement a yeast mutant deficient in potassium (K⁺) uptake. Two genes were cloned that complemented the mutant: HKT1 and a novel cDNA described in this report encoding a cation transporter, LCT1 (low-affinity cation transporter). Analysis of the secondary structure of LCT1 suggests that the protein contains 8–10 transmembrane helices and a hydrophilic amino terminus containing sequences enriched in Pro, Ser, Thr, and Glu (PEST). The transporter activity was assayed using radioactive isotopes in yeast cells expressing the cDNA. LCT1 mediated low-affinity uptake of the cations Rb⁺ and Na⁺, and possibly allowed Ca²⁺ but not Zn²⁺ uptake. LCT1 is expressed in low abundance in wheat roots and leaves. The precise functional role of this cation transporter is not known, although the competitive inhibition of cation uptake by Ca²⁺ has parallels to whole plant and molecular studies that have shown the important role of Ca²⁺ in reducing Na⁺ uptake and ameliorating Na⁺ toxicity. The structure of this higher plant ion transport protein is unique and contains PEST sequences.