Integrated transcriptome and metabolome analysis reveals the mechanisms of exogenous melatonin in mitigating drought stress in Camellia hainanica

Drought stress (D) significantly impairs plant growth; however, melatonin (MT) has been shown to mitigate these adverse effects, although such responses have not yet been reported in Camellia hainanica . In this study, we evaluated physiological parameters and enzyme activities across three groups: control (CK), drought stress (D), and drought stress with MT treatment (D_MT). The results showed that D induced stomatal closure, whereas MT alleviated this effect. The D_MT group exhibited approximately 16 % higher chlorophyll a, chlorophyll b, and carotenoid contents compared with the other two groups. In addition, antioxidant enzyme activity in the D group was reduced by about 29 % relative to the CK group, indicating that MT counteracts D-induced oxidative damage in plants. Integrated transcriptomic and metabolomic analyses further revealed that MT modulates galactose metabolism and its catabolic processes under D, with INV1 , INV3 , and GLA5–7 involved in the alleviation mechanism. Overall, MT mitigates D in C. hainanica by regulating stomatal structure, enhancing photosynthetic pigment synthesis, reducing reactive oxygen species (ROS) accumulation through elevated enzyme activity, and modulating galactose metabolism. These findings highlight the role of MT in enhancing D tolerance of C. hainanica , providing a theoretical and technical basis for drought-resilient cultivation management, supporting the sustainable development of the C. hainanica industry, and offering scientific evidence for the application of MT in agricultural production. • Melatonin (MT) enhances chlorophyll content and improves gas exchange in C. hainanica . • MT mitigates drought (D) stress-induced stomatal closure in C. hainanica . • The D stress reduces antioxidant enzyme activity in C. hainanica by 29 %, whereas MT promotes antioxidant enzyme activity. • In galactose metabolism, the INV and GLA genes are involved in the MT-mediated alleviation of D.