Genes Encoding Proteins of the Cation Diffusion Facilitator Family That Confer Manganese Tolerance

Abstract

The yeast Saccharomyces cerevisiae expressing a cDNA library prepared from Stylosanthes hamata was screened for enhanced Mn²⁺ tolerance. From this screen, we identified four related cDNAs that encode membrane-bound proteins of the cation diffusion facilitator (CDF) family. One of these cDNAs (ShMTP1) was investigated in detail and found to confer Mn²⁺ tolerance to yeast by internal sequestration rather than by efflux of Mn²⁺. Expression of ShMTP1 in a range of yeast mutants suggested that it functions as a proton:Mn²⁺ antiporter on the membrane of an internal organelle. Similarly, when expressed in Arabidopsis, ShMTP1 conferred Mn²⁺ tolerance through internal sequestration. The ShMTP1 protein fused to green fluorescent protein was localized to the tonoplast of Arabidopsis cells but appeared to localize to the endoplasmic reticulum of yeast. We suggest that the ShMTP1 proteins are members of the CDF family involved in conferring Mn²⁺ tolerance and that at least one of these proteins (ShMTP1) confers tolerance by sequestering Mn²⁺ into internal organelles.