Supplementation with plant growth promoting rhizobacteria (PGPR) alleviates cadmium toxicity in Solanum lycopersicum by modulating the expression of secondary metabolites.

The current study evaluated the synergistic role of Plant growth promoting rhizobacteria (PGPR), Pseudomonas aeruginosa and Burkholderia gladioli on different physiological, biochemical and molecular activities of 10-days old Solanum lycopersicum seedlings under Cd stress. Cd toxicity altered the levels of phenolic compounds (total phenols (30.2%), flavonoids (92.7%), anthocyanin (59.5%), polyphenols (368.7%)), osmolytes (total osmolytes (10.3%), total carbohydrates (94%), reducing sugars (64.5%), trehalose (112.5%), glycine betaine (59%), proline (54.8%), and free amino acids (63%)), and organic acids in S. lycopersicum seedlings. Inoculation of P. aeruginosa and B. gladioli alleviated Cd-induced toxicity, which was manifested through enhanced phenolic compound levels and osmolytes. Additionally, the levels of low molecular weight organic acids (fumaric acid, malic acid, succinic acid, and citric acid) were also elevated. The expression of genes encoding enzymes for phenols and organic acid metabolism were also studied to be modulated that included CHS (chalcone synthase; 138.4%), PAL (phenylalanine ammonia lyase; 206.7%), CS (citrate synthase; 61.3%), SUCLG1 (succinyl Co-A ligase; 33.6%), SDH (succinate dehydrogenase; 23.2%), FH (fumarate hydratase; 12.4%), and MS (malate synthase; 41.2%) and found to be upregulated in seedlings inoculated independently with P. aeruginosa and B. gladioli. The results provide insights into the role of micro-organisms in alleviating Cd-induced physiological damage by altering levels of different metabolites.