9.A.43 The Cadmium tolerance Efflux Pump (CTEP) Family
Cadmium (Cd) causes the generation of reactive oxygen species (ROS), which in turn causes cell damage. Kim et al (2008
) isolated a novel gene from a wheat root cDNA library, which conferred Cd(II)-specific tolerance when expressed in Saccharomyces cerevisiae
. The gene, called TaTM20, for Triticum aestivum
transmembrane 20, encodes a putative hydrophobic polypeptide of 889 amino acids, containing 20 transmembrane domains arranged as a 5-fold internal repeating unit of 4 transmembrane domains each. Expression of TaTM20 in yeast cells stimulated Cd(II) efflux resulting in a decrease in the content of yeast intracellular Cd. TaTM20-induced Cd(II) tolerance was maintained in yeast even under conditions of reduced glutathione (GSH). Thus, TaTM20 enhances Cd(II) tolerance in yeast through the stimulation of Cd(II) efflux from the cell, partially independent of GSH. Treatment of wheat seedlings with Cd(II) induced their expression of TaTM20, decreasing subsequent root Cd(II) accumulation and suggesting a possible role for TaTM20 in Cd(II) tolerance in wheat.