Cadmium tolerance and accumulation in Indian mustard is enhanced by overexpressing gamma-glutamylcysteine synthetase

To investigate rate-limiting factors for glutathione and phytochelatin (PC) production and the importance of these compounds for heavy metal tolerance , Indian mustard (Brassica juncea) was genetically engineered to overexpres s the Escherichia coli gshl gene encoding gamma-glutamylcysteine synthetase (gamma-ECS), targeted to the plastids. The gamma-ECS transgenic seedlings showed increased tolerance to Cd and had higher concentrations of PCs, gamm a-GluCys, glutathione, and total non-protein thiols compared with wild-type (WT) seedlings. When tested in a hydroponic system, gamma-ECS mature plant s accumulated more Cd than WT plants: shoot Cd concentrations were 40% to 9 0% higher. In spite of their higher tissue Cd concentration, the gamma-ECS plants grew better in the presence of Cd than WT. We conclude that overexpr ession of gamma-ECS increases biosynthesis of glutathione and PCs, which in turn enhances Cd tolerance and accumulation. Thus, overexpression of gamma -ECS appears to be a promising strategy for the production of plants with s uperior heavy metal phytoremediation capacity.