Integrated transcriptomic and metabolomic analyses reveal drought-response mechanisms in Suriana maritima from tropical coral islands

Drought is a major abiotic stress limiting plant survival on tropical coral islands. Suriana maritima, an ecologically important shrub species in the Xisha Islands, shows strong adaptation to harsh coastal environments, but its molecular responses to drought remain poorly understood. Here, we integrated transcriptomic and metabolomic analyses to characterize leaf responses of S. maritima to progressive drought stress. Severe drought induced extensive transcriptional and metabolic reprogramming, accompanied by leaf yellowing, wilting and partial shedding. Stress-related genes, including those encoding chitinases, late embryogenesis abundant proteins, glutathione S-transferase and glutathione peroxidase, were up-regulated, suggesting enhanced oxidative stress protection and defense-related responses. Genes involved in plant hormone signaling pathways, particularly abscisic acid, jasmonic acid, gibberellin and ethylene, also showed marked transcriptional changes. In contrast, photosynthesis-associated genes, especially those related to photosystems and light-harvesting complexes, were strongly repressed under severe drought but were rapidly reactivated after rehydration, indicating indicating reversible suppression of photosynthetic activity. Metabolomic profiling showed accumulation of amino acids and lipids, including tryptophan, valine and lysophosphatidylethanolamine, whereas many flavonoids and phenylpropanoid-related metabolites declined. Integrated analysis identified coordinated repression of flavonoid and phenylpropanoid biosynthesis under severe drought. These results suggest that S. maritima responds to severe drought by reallocating resources from photosynthesis and secondary metabolite biosynthesis toward stress protection, antioxidant defense, and recovery capacity. This study provides molecular insight into drought adaptation in a non-model coastal plant and offers useful baseline information for future conservation and vegetation restoration strategies on tropical coral islands.