Transcriptomic and physiological analyses reveal changes in secondary metabolite and endogenous hormone in ginger (Zingiber officinale Rosc.) in response to postharvest chilling stress

Storing postharvest ginger at low temperatures can extend its shelf life, but can also lead to chilling injury, loss of flavor, and excessive water loss. To investigate the effects of chilling stress on ginger quality, morphological, physiological, and transcriptomic changes were examined after storage at 26 °C, 10 °C, and 2 °C for 24 h. Compared to 26 °C and 10 °C, storage at 2 °C significantly increased the concentrations of lignin, soluble sugar, flavonoids, and phenolics, as well as the accumulation of H2O2, O2-, and thiobarbituric acid reactive substances (TBARS). Additionally, chilling stress inhibited the levels of indoleacetic acid, while enhancing gibberellin, abscisic acid, and jasmonic acid, which may have increased postharvest ginger's adaptation to chilling. Storage at 10 °C decreased lignin concentration and oxidative damage, and induced less fluctuant changes in enzymes and hormones than storage at 2 °C. RNA-seq revealed that the number of differentially expressed genes (DEGs) increased with decreasing temperature. Functional enrichment analysis of the 523 DEGs that exhibited similar expression patterns between all treatments indicated that they were primarily enriched in phytohormone signaling, biosynthesis of secondary metabolites, and cold-associated MAPK signaling pathways. Key enzymes related to 6-gingerol and curcumin biosynthesis were downregulated at 2 °C, suggesting that cold storage may negatively impact ginger quality. Additionally, 2 °C activated the MKK4/5-MPK3/6-related protein kinase pathway, indicating that chilling may increase the risk of ginger pathogenesis.