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 ( Bs Si) alleviating the oxidative damage caused by salt-drought stress on G. uralensis . The results showed that Bs Si 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 (H 2 O 2 ) and superoxide anion (O 2 − ·), and reducing the accumulation of malondialdehyde (MDA). Meanwhile, Bs Si 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.