The plant cDNA LCT1 mediates the uptake of calcium and cadmium in yeast

Nonessential metal ions such as cadmium are most likely transported across plant membranes via transporters for essential cations. To identify possible pathways for Cd(2+) transport we tested putative plant cation transporters for Cd(2+) uptake activity by expressing cDNAs in Saccharomyces cerevisiae and found that expression of one clone, LCT1, renders the growth of yeast more sensitive to cadmium. Ion flux assays showed that Cd(2+) sensitivity is correlated with an increase in Cd(2+) uptake. LCT1-dependent Cd(2+) uptake is saturable, lies in the high-affinity range (apparent K(M) for Cd(2+) = 33 μM) and is sensitive to block by La(3+) and Ca(2+). Growth assays demonstrated a sensitivity of LCT1-expressing yeast cells to extracellular millimolar Ca(2+) concentrations. LCT1-dependent increase in Ca(2+) uptake correlated with the observed phenotype. Furthermore, LCT1 complements a yeast disruption mutant in the MID1 gene, a non-LCT1-homologous yeast gene encoding a membrane Ca(2+) influx system required for recovery from the mating response. We conclude that LCT1 mediates the uptake of Ca(2+) and Cd(2+) in yeast and may therefore represent a first plant cDNA encoding a plant Ca(2+) uptake or an organellar Ca(2+) transport pathway in plants and may contribute to transport of the toxic metal Cd(2+) across plant membranes.