From photosynthesis to secondary metabolism: Melatonin orchestrates 6-gingerol biosynthesis and stress tolerance in Zingiber officinale under aluminum stress

Global soil acidification intensifies aluminum (Al) toxicity, posing an increasing threat to the productivity and industrial value of ginger. While melatonin (MT) is known to alleviate abiotic stress in various plants, its specific effects on ginger under Al stress remain unclear. Furthermore, whether MT-mediated physiological regulation influences the biosynthesis of bioactive compounds in ginger under Al stress has not been investigated. Here, we investigated the mechanisms by which exogenous MT alleviates Al stress in ginger and explored its impact on secondary metabolism. Exposure to 750 mg kg −1 Al 3+ (MT0) reduced ginger yield by 43.5%, decreased chlorophyll a content by 81.65%, and caused severe chloroplast damage. Application of 200 μM MT (MT200) proved most effective, reducing Al content by 66.8%. MT200 enhanced net photosynthetic rate (Pn) and photosystem II efficiency (Y(II)) by 90.8% and 98.2%, respectively, while increasing peroxidase (POD) and superoxide dismutase (SOD) activities by 102.2% and 40.8%. Consequently, H 2 O 2 and malondialdehyde (MDA) contents were reduced by 37.3% and 50.1%. Regarding secondary metabolism, MT200 significantly increased 6-gingerol, 8-gingerol, and 8-shogaol contents by 17.0%, 23.3%, and 103.8%, respectively. Notably, cyclic electron flow (CEF) and POD activity were identified as key predictors of 6-gingerol accumulation. Furthermore, co-expression analysis revealed a strong association between photosynthetic genes ( ZoPsbA , ZoPsaB ) and a key gingerol biosynthetic gene ( ZoPKS ). These findings uncover a mechanism by which melatonin orchestrates 6-gingerol biosynthesis through coordinating photosynthetic carbon supply and redox homeostasis. This study identifies 200 μM MT as the optimal concentration for improving ginger productivity and quality in acidic soils, providing a theoretical basis for cultivation practices. • Melatonin alleviated the aluminum stress of ginger. • Melatonin protected the chloroplast structure under aluminum stress. • Melatonin maintained high photosynthetic performance under aluminum stress. • Cyclic electron flow and peroxidase activity showed a potential link to 6-gingerol accumulation. • ZoPsbO synergized with ZoPKS to affect the synthesis of 6-gingerol.