Synchronous overexpression of glutathione-S-transferase and cyanidase maintains the redox homeostasis ‎and improves cyanide remediation capacity in tobacco

Genetically engineered plants could provide feasible and environmentally safe approach for phytoremediation of CN compounds. However, the survival capacity of transgenic plants under high doses of CN is disappointing. One of the possible causes of such phytotoxicity is the CN-induced inhibition of antioxidant systems that lead to accumulation of reactive oxygen species (ROS). Therefore, simultaneous overexpression of a CN degrading enzyme along with an ‎oxidative stress-relieving protein could maintain the internal redox homeostasis and enhance CN-phytoremediation capacity under high doses of CN. In the present study, transgenic tobacco plants overexpressing the ‎bacterial cyanidase (CYND) and the cyanobacterial glutathione-S-transferase (GST) separately ‎and ‎in combination have been generated. Significant growth recovery was observed for all transgenic plants under 10 mM CN compared to wild type plants. However, GST + CYND overexpressors showed the highest biomass accumulation under CN stress. Similarly, reduction in photosynthetic pigments and total carbohydrate levels were significantly recovered in transgenic plants especially at higher doses of CN (7.5 and 10.0 mM). Moreover, both GST and GST + CYND transgenic plants showed elevated activities of SOD and CAT compared to the wild type upon exposure to CN. MDA content, as an indicator of lipid peroxidation, was significantly decreased in all transgenic plants. However, the lowest level of MDA was observed in GST + CYND transgenic lines. These results suggest that synchronous overexpression of GST with CYND genes improves CN remediation capacity of tobacco by improvement of the antioxidant scavenging systems and keeping ROS under control.