Bacillus cooperated with silicon mediating antioxidant enzymes, non-enzymatic antioxidants and osmotic adjustment substances metabolism to mitigate oxidative damage of Glycyrrhiza uralensis Fisch. exposed to salt and drought stress

Salt and drought as major abiotic stresses often co-occur in the natural environment, which significantly hinders crop productivity mainly due to oxidative damage. Antioxidant systems play a crucial role in enabling plants to resist abiotic stress. Our previous research found that Bacillus G2+G5 (Bs) combined with silicon (Si) alleviated the adverse effect of salt-drought stress on Glycyrrhiza uralensis Fisch (G. uralensis) through modulating oxidative stress. This study, through physiological and biochemical measurements, as well as transcriptome analysis, explores the regulatory mechanism of Bs combined with Si (BsSi) alleviating the oxidative damage caused by salt-drought stress on G. uralensis. The results showed that BsSi enhanced the antioxidant enzymes such as catalase (CAT), and glutathione peroxidase (GPX) activities, optimized the ascorbate-glutathione (AsA-GSH) cycle and sugar metabolism, up-regulated the expression of genes encoding phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), and ζ-carotene isomerase (Z-ISO) related to flavonoids and carotenoids synthesis, thereby directly enhancing the scavenging rate of hydrogen peroxide (H2O2) and superoxide anion (O2−·), and reducing the accumulation of malondialdehyde (MDA). Meanwhile, BsSi up-regulated fatty acid metabolism-related genes such as long-chain acyl-CoA synthetase (LACS) and aldehyde dehydrogenase (ALDH), promoted the accumulation of osmoregulatory substances (including proline, γ-aminobutyric acid, betaine, and polyamines), maintained cell membrane stability and osmotic balance, thereby indirectly inhibiting ROS accumulation and lipid peroxidation. This study provides a new perspective for elucidating the mechanism of PGPB and Si synergistically regulating plant oxidative stress, and lays a theoretical foundation for studying the mechanism of plant salt tolerance and drought resistance.