Novel Cysteine-Rich Peptides from Digitaria ciliaris and Oryza sativa Enhance Tolerance to Cadmium by Limiting its Cellular Accumulation

By means of functional screening using the cadmium (Cd)-sensitive ycf1 yeast mutant, we have isolated a novel cDNA clone, DcCDT1, from Digitaria ciliaris growing in a former mining area in northern Japan, and have shown that it confers Cd tolerance to the yeast cells, which accumulated almost 2-fold lower Cd levels than control cells. The 521bp DcCDT1 cDNA contains an open reading frame of 168bp and encodes a deduced peptide, DcCDT1, that is 55 amino acid residues in length, of which 15 (27.3) are cysteine residues. Five DcCDT1 homologs (here termed OsCDT1OsCDT5) have been identified in rice, and all of them were up-regulated to varying degrees in the above-ground tissues by CdCl2 treatment. Localization of green fluorescent protein fusions suggests that DcCDT1 and OsCDT1are targeted to both cytoplasmic membranes and cell walls of plant cells. Transgenic Arabidopsis thaliana plants overexpressing DcCDT1 or OsCDT1 displayed a Cd-tolerant phenotype and, consistent with our yeast data, accumulated lower amounts of Cd when grown on CdCl2. Collectively, our data suggest that DcCDT1 and OsCDT1 function to prevent entry of Cd into yeast and plant cells and thereby enhance their Cd tolerance.