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

TLDR: The structure of this higher plant ion transport protein is unique and contains PEST sequences, which suggests that the protein contains 8-10 transmembrane helices and a hydrophilic amino terminus containing sequences enriched in Pro, Ser, Thr, and Glu (PEST).

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