Cloning and characterization of γ-glutamylcysteine synthetase in the salt- and oxidative stress-tolerant wild tomato species Solanum pennellii under abiotic stresses

The wild species of tomato Solanum pennellii (Lpa) is more tolerant to salt-induced oxidative stress than the cultivated species Solanum lycopersicum (Lem), due to the increase of several antioxidative metabolites and enzymes in this species under stress. The increase of reduced glutathione (GSH), one of these metabolites, in NaCl-treated Lpa, is due at least partly to the elevation of γ-glutamylcysteine synthetase (γ-ECS). Introgression line IL 8-3, which was found to include the Lpa orthologue of the γ-ECS gene (Lpa γ-ECS) in Lem's genetic background, was used to assign this gene to chromosome 8 and to assess its relative contribution to the effective antioxidative response of Lpa to stress. The growth of IL 8-3 and Lem plants responded similarly to NaCl and cadmium (Cd) stresses. In both genotypes, GSH and H₂O₂ levels responded also similarly to NaCl stress. NaCl and Cd stresses affected similarly the transcription of the γ-ECS gene in leaves of both IL 8-3 and Lpa plants. The effect of buthionine sulfoximine (BSO), a competitive inhibitor of the γ-ECS enzyme, on γ-ECS transcription was also similar in these two genotypes. Taken together, these results suggest that γ-ECS orthologues differ mainly in the regulation of their transcription and not at the post-transcriptional or translational levels. The mutation(s) led to these differences in the response of the two orthologues to the salinity and heavy metal stresses are expected to occur in a cis-regulatory element(s) located relatively close to γ-ECS.