Overexpression of AtATM3 in Brassica juncea confers enhanced heavy metal tolerance and accumulation

AtATM3, a member of the ATP-binding cassette transporter family, is localized at the mitochondrial membrane of Arabidopsis thaliana and is involved in the biogenesis of Fe–S clusters and iron homeostasis in plants. Through Agrobacterium-mediated genetic transformation, the AtATM3 gene driven by the cauliflower mosaic virus 35S promoter (CaMV35S) was introduced into Brassica juncea (Indian mustard), a plant species suitable for phytoremediation, with the aim of improving heavy metal tolerance and accumulation in plants. The presence of the AtATM3 gene in transgenic plants was confirmed by polymerase chain reaction (PCR). Reverse transcriptase-PCR analysis confirmed AtATM3 expression in transgenic plants, but the level of AtATM3 expression varied between lines. AtATM3 overexpression in B. juncea conferred enhanced tolerance to cadmium [Cd(II)] and lead [Pb(II)] stresses. Importantly, the shoot tissues of transgenic seedlings contained about 1.5- to 2.5-fold higher Cd(II) and Pb(II) levels than wild type (WT) seedlings, demonstrating significantly-increased accumulation of both Cd(II) and Pb(II) in transgenic plants. The enhanced capacity of heavy metal tolerance and accumulation by AtATM3 transgenic plants was attributed to higher BjGSHII (B. juncea glutathione synthetase II) and BjPCS1 (phytochelatin synthase 1) expression levels induced by AtATM3 overexpression. In addition, AtATM3 overexpression regulated the expression of several metal transporters in the transgenic B. juncea plants under heavy metal stress conditions. Therefore, AtATM3 transgenic plants are more tolerant of and can accumulate more heavy metals to enhance phytoremediation of contaminated soils.