Assessment of Drought Stress Resilience Through Serendipita indica Endophytism in Tobacco

Drought is an increasingly frequent constraint for flue-cured tobacco production. Here we reported the root endophyte Serendipita indica enhancing drought tolerance in Nicotiana tabacum L. (cv. Yunyan 87) and identified the underlying mechanisms using integrated physiology and metabolomics. Seedlings were inoculated with a root-zone drench of S. indica mycelium/chlamydospore suspension (15 mL per plant, repeated after 3 days), and colonization was confirmed microscopically. Drought markedly decreased net photosynthesis, stomatal conductance, transpiration, intercellular CO₂, and total chlorophyll, whereas inoculated plants maintained significantly higher gas-exchange parameters and chlorophyll contents than drought-only plants. Antioxidant defense was strengthened under S.i + D, with increased SOD, POD and CAT activities. It reduced H₂O₂ and malondialdehyde in both leaves and roots, accompanied by greater proline and soluble sugar accumulation. UPLC-MS metabolomics revealed pronounced reprogramming: drought altered 168 leaf metabolites (71 up/97 down) and 215 root metabolites (111 up/104 down) relative to CTRL, while S.i + D altered 137 leaf metabolites (78 up/59 down) and 227 root metabolites (117 up/110 down); compared with drought-only plants, S. indica shifted 100 leaf (55 up/45 down) and 81 root metabolites (41 up/40 down). S. indica reduced drought-associated tropane/pyridine alkaloid signatures while promoting protective polyols and benzenoids. S. indica improves tobacco drought resilience by coordinating photosynthetic preservation with redox buffering, osmotic adjustment and targeted carbon/nitrogen rerouting, identifying flavonoid and arginine-proline modules as key metabolic nodes for endophyte-assisted drought tolerance, opening the doors for further research leading towards the way of constructing a sustainable environment of fungi-plant interactions.