Integrated transcriptomic-metabolomic analysis reveals cellular responses of harvested strawberry fruit subjected to short-term exposure to high levels of carbon dioxide

Harvested strawberry (Fragaria × ananassa) fruit has a short shelf life due to rapid postharvest metabolism, quick softening, mechanical damage, and fungal decay. To improve the storability of strawberry fruit, we subjected harvested fruit to short-term exposure to 30% carbon dioxide (CO2) and used transcriptomic and metabolomic analyses to identify the cellular responses induced by this treatment. Fruit was stored at 10 °C for 10 d after a 3-h exposure to 30% CO2 (treatment) or ambient air (control) at 25 °C, respectively. The CO2 treatment reduced fruit decay and softening compared to the control throughout the 10-d storage period. Transcriptomic analyses revealed that expression levels of genes encoding cell wall-degrading enzymes (expansin, pectinesterase, and β-xylosidase) decreased in response to the CO2 treatment. Within 1 d after the CO2 treatment, the expression levels of genes encoding heat-shock proteins significantly increased. Metabolite profiling revealed that glucose, quinic acid, and succinic acid increased in responses to the CO2 treatment at 1 d. Transmission electron microscopy showed that disintegration of the middle lamella in the cell wall was inhibited by the CO2 treatment. Polyuronide (insoluble pectin) content in cell walls was 30% higher, on average, in the treated fruit than those in the control fruit during the 10-d storage period. These results indicate that a short-term treatment with 30% CO2 reduces the degradation of pectin in the cell wall by reducing the activity of cell wall-degrading enzymes and induces abiotic stress-response genes in harvested strawberry fruit. Our results improve our understanding of the molecular mechanisms behind CO2-responsive genes in strawberry fruit and provide insight into ways to improve the postharvest quality of strawberries.