Physiological and transcriptomic responses of Ginkgo biloba to salt stress and exogenous melatonin.

INTRODUCTION: Soil salinization constrains plant growth, and enhancing salt tolerance is of great significance. METHODS: Here, Ginkgo biloba seedlings were treated with control (CK), salt stress (S), or salt stress + melatonin (S+M). Integrating physiology, transcriptomics, and weighted gene co-expression network analysis (WGCNA), we explored how melatonin enhances salt tolerance. RESULTS AND DISCUSSION: Salt stress reduced chlorophyll content, suggesting potential impairment of photosynthetic capacity, appeared to increase membrane lipid peroxidation, and led to substantial proline accumulation. Melatonin treatment appeared to up-regulate the MAPK gene MYC2 and down-regulate PP2C and RbohD, suggesting a potential alleviation of oxidative stress. WGCNA identified MEblue (MAPK-enriched) positively correlated with salt stress and proline, and MEgreen (photosynthesis-enriched) positively correlated with chlorophyll and catalase (CAT) activity but negatively correlated with salt stress. Melatonin appeared to help restore MEgreen expression, potentially reducing oxidative damage and appearing to help stabilize chlorophyll. Melatonin also appeared to help maintain photosystem II (PSII) genes (Lhcb1, Lhcb4) and reduced flavonoid accumulation. These findings provide insights into the model of melatonin-mediated salt stress responses in gymnosperms. This work may support salt-tolerant Ginkgo biloba breeding and the application of melatonin in forestry.