The Brassica juncea BjCdR15, an ortholog of Arabidopsis TGA3, is a regulator of cadmium uptake, transport and accumulation in shoots and confers cadmium tolerance in transgenic plants

P>A bZIP transcription factor from Brassica juncea (BjCdR15) was isolated by the cDNA-amplified fragment length polymorphism technique after cadmium treatment. Sequence analysis indicated high similarity between BjCdR15 and Arabidopsis TGA3. In Arabidopsis, TGA3 transcription is also induced by cadmium; hence, we investigated whether BjCdR15 is involved in cadmium tolerance and whether it can functionally replace TGA3 protein in Arabidopsis tga3-2 mutant plants. BjCdR15 expression was detected mainly in the epidermis and vascular system of cadmium-treated plants, and increased in roots and leaves after cadmium treatment. The overexpression of BjCdR15 in Arabidopsis and tobacco enhanced cadmium tolerance: overexpressing plants showed high cadmium accumulation in shoots. Conversely, Arabidopsis tga3-2 mutant plants showed high cadmium content in roots and inhibition of its transport to the shoot. We demonstrated that BjCdR15 can functionally replace TGA3: in 35S::BjCdR15-tga3-2 plants, the long-distance transport of cadmium from root to shoot was restored and these plants showed an increased cadmium content in shoots compared with all other assays. In addition, BjCdR15/TGA3 regulated the synthesis of phytochelatin synthase and the expression of several metal transporters. The results indicate that BjCdR15/TGA3 transcription factors play a crucial role in the regulation of cadmium uptake by roots and in its long-distance root to shoot transport. BjCdR15/TGA3 may thus be considered as useful candidates for potential biotechnological applications in the phytoextraction of cadmium from polluted soils.