Exploring the variety-specific roles of glutathione transferases in tomato osmotic stress response

Osmotic stress induces the overproduction of reactive oxygen species (ROS), leading to oxidative damage to cellular components, with lipid peroxidation being one of the most harmful consequences. Glutathione transferases (GSTs; E.C. 2.5.1.18) play a key role in detoxifying harmful compounds through their glutathione transferase and glutathione peroxidase (GPOX) activities. To investigate the specific roles of GSTs in tomato responses to osmotic stress, two cultivars of Solanum lycopersicum (cv. Mobil and Moneymaker) were treated with increasing concentrations of polyethylene glycol (PEG 6000) over several days. Both cultivars exhibited similar symptoms of severe stress, but their enzymatic activity and the expression of GST genes differed. These gene expression patterns indicate that a specific group of tomato GSTs, including certain Tau and Theta class GSTs (GSTUs and GSTTs), may play an important role in defending against osmotic stress across various tomato varieties. Additionally, the gene expression profiles of the two cultivars likely correspond to the differences observed in their enzymatic activity: elevated GST and GPOX activity in Mobil, but in Moneymaker, solely the GPOX activity was increased. Particular focus was given to the tomato Theta class GSTs (SlGSTTs), known for their GPOX activity and substrate preference for lipid peroxides. Marked upregulation was observed of SlGSTT genes under osmotic stress. Protein modeling and molecular docking suggest that SlGSTT2 and SlGSTT3 isoenzymes may contribute to membrane protection by scavenging different lipid peroxidation products in the peroxisomes.