Photoperiod-mediated transcriptional and metabolic reprogramming confers salt stress tolerance via the ascorbate-glutathione cycle and phenylpropanoid pathway in Ginkgo biloba

Ginkgo biloba, one of the oldest extant relict tree species, is highly valued for its medicinal properties. However, soil salinization has emerged as a severe global ecological challenge, substantially restricting plant growth, development, and geographical distribution. While light signaling, particularly photoperiod, is a critical environmental cue, its specific role in the salt stress adaptation of G. biloba remains largely elusive. In this study, we employed a multi-omics approach to analyze the complex mechanisms underlying the responses to salt stress under long-day and short-day conditions. Our results revealed that long-day treatment significantly enhanced salt stress tolerance compared to the short-day condition. Under long-day conditions, plants exhibited significantly higher activities of superoxide dismutase and catalase, which effectively scavenged reactive oxygen species and mitigated membrane lipid peroxidation under salt stress. In parallel, these plants accumulated higher levels of key metabolites such as phenylpropanoids, flavonoids and reduced glutathione. Integrated transcriptomic and metabolomic analyses indicated that the long-day regime mitigates salt stress by coordinately modulating glutathione metabolism, phenylpropanoid biosynthesis, and flavonoid biosynthesis pathways. Crucially, the expression patterns of key biosynthetic genes aligned consistently with the observed accumulation levels of these metabolites. Taken together, these findings demonstrate that long-day conditions enhance salt tolerance in G. biloba by promoting the accumulation of ascorbate-glutathione cycle components and secondary metabolites, thereby strengthening its antioxidant and detoxification capacities. These insights reveal a photoperiod-dependent metabolic reprogramming mechanism, advancing our understanding of how environmental light cues modulate abiotic stress resilience in woody perennial species.