Assessment of the Cadmium and Copper Phytoremediation Potential of the Lobularia maritima Thioredoxin 2 Gene Using Genetically Engineered Tobacco

Rapid global modernization, urbanization, and industrialization have accelerated the release of heavy metals, causing soil pollution. These highly noxious environmental pollutants induce oxidative stress in plants via stimulation of the production of reactive oxygen species (ROS). Thioredoxin (Trxs) is a highly conserved disulfide reductase that plays a crucial role in intracellular redox homeostasis in both eukaryotes and prokaryotes. Herein, the presence of heavy metals highly upregulated LmTrxh2 transcription in Lobularia maritima seedlings and its overexpression-conferred tolerance to Cd, Cu, Mn, and Zn in Saccharomyces cerevisiae. In addition, LmTrxh2-overexpressing tobacco plants had higher seedling survival rates than non-transgenic plants (NT), with enhanced root length and biomass production and reduced ROS accumulation, following Cd and Cu stress. These plants also accumulated more Cd, Cu, and Mn than the NT plants. Moreover, LmTrxh2 overexpression stimulated the transcription of genes encoding metallothioneins (Met-1, Met-2, Met-3, and Met-4), a copper transport protein, a Snakin/GASA protein (Snakin-2), and ROS-scavenging enzymes (SOD, APX1, and CAT), which might contribute to heavy metal tolerance in tobacco plants. These results suggest that LmTrxh2 overexpression helps to improve heavy metal tolerance by stimulating antioxidant capacities and the expression of several stress-responsive genes in plants.