A reciprocal metabolic switch between glycolysis and gluconeogenesis is associated with sugar retention during postharvest cold storage in sweet corn

Sweet corn deteriorates rapidly after harvest as persistent respiration and sugar turnover reduce sweetness and market quality. Low-temperature storage delays this deterioration, but the central carbon responses associated with sugar retention remain incompletely understood. Here, we integrated quality measurements, transcriptome profiling, enzyme activity assays, and targeted metabolite analyses in sweet corn (‘Hetianyu 818’) stored at 5 °C or 25 °C for 10 days. Compared with kernels stored at 25 °C, those stored at 5 °C showed slower yellowing and texture deterioration and retained higher glucose, fructose and sucrose contents. At day 10, the contents of glucose, fructose, and sucrose at 5 °C were significantly higher than those at 25 °C by 2.99-, 5.51-, and 7.74-fold, respectively. KEGG enrichment and weighted gene co-expression network analysis identified glycolysis/gluconeogenesis as a major pathway associated with temperature-dependent sugar variation. ZmPFK6 expression and phosphofructokinase activity were higher at 25 °C, consistent with greater glycolytic capacity, whereas ZmPEPCK2 expression and phosphoenolpyruvate carboxykinase activity were higher at 5 °C, consistent with greater capacity for gluconeogenic carbon recycling. Time-resolved metabolite profiling identified 87 temperature-responsive differential metabolites, of which 79 were more abundant and 8 less abundant under cold storage. At day 10, phosphoenolpyruvate, fructose 1,6-bisphosphate, and fructose 6-phosphate were 4.64-, 3.55-, and 8.57-fold more abundant, respectively, at 5 °C than at 25 °C. Together, these transcriptional, enzymatic, and metabolic associations support a working model in which contrasting glycolytic and gluconeogenic responses are associated with sugar retention during cold storage, and prioritize ZmPFK6 and ZmPEPCK2 as candidates for further functional validation.