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 Cd²⁺ transport we tested putative plant cation transporters for Cd²⁺ 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 Cd²⁺ sensitivity is correlated with an increase in Cd²⁺ uptake. LCT1-dependent Cd²⁺ uptake is saturable, lies in the high-affinity range (apparent K(M) for Cd²⁺ = 33μM) and is sensitive to block by La²⁺ and Ca²⁺. Growth assays demonstrated a sensitivity of LCT1-expressing yeast cells to extracellular millimolar Ca²⁺ concentrations. LCT1-dependent increase in Ca²⁺ uptake correlated with the observed phenotype. Furthermore, LCT1 complements a yeast disruption mutant in the MIDI gene, a non-LCTl-homologous yeast gene encoding a membrane Ca²⁺ influx system required for recovery from the mating response. We conclude that LCT1 mediates the uptake of Ca²⁺ and Cd²⁺ in yeast and may therefore represent a first plant cDNA encoding a plant Ca²⁺ uptake or an organellar Ca²⁺ transport pathway in plants and may contribute to transport of the toxic metal Cd²⁺ across plant membranes.