UC Davis

Postharvest chilling injury (PCI) is a physiological disorder that contributes to the global loss and waste of fruit and vegetables. Ectopic expression of C-Repeat Binding Factor (CBF) transcription factors in tomato (Solanum lycopersicum L.) alleviates vegetative chilling injury, but their influence on PCI is unknown. We developed a dexamethasone (DEX)-inducible system with the aim of limiting high ectopic expression of Arabidopsis thaliana CBF1 (AtCBF1) to fruit, and only during postharvest chilling. Our aim was (1) to optimize the DEX-inducible system for high AtCBF1 expression in the organ and conditions of interest, i.e., fruit postharvest cold storage, and (2) to determine if AtCBF1 could lessen PCI symptoms. Here, we describe the testing and validation of transformed lines from this system. In all tests, fruit were stored under PCI-inducing or non-PCI-inducing conditions. Across storage time, fruit immersion in 50 μM DEX for one hour prior to 2.5 °C storage or rewarming, induced AtCBF1 expression 11- to 91-fold (mean: 33-fold, median: 29-fold), significantly higher than the 0.2- to 3.2-fold (mean: 1.5-fold, median: 1.3-fold) without DEX. Fruit color, surface pitting and decay incidence were used to indicate PCI. For genotype OE-8, PCI symptoms lessened during cold storage without DEX application compared to the wild-type. For line OE-2, DEX led to riper fruit at both 2.5 and 12.5 °C, while PCI-like symptoms developed under control temperatures (12.5 °C), after rewarming. In OE-6 fruit, DEX elicited a mild increase in the rate of ripening during the first week of cold storage compared to the wild-type. Our findings show that AtCBF1 ectopic expression influenced fruit surface color or PCI symptom-development, and highlight that PCI is tightly interconnected with ripening. This is the first report of the use of a chemical-inducible system to ectopically express a gene to study a postharvest trait, and provides a basis for investigating the role of CBF1 on PCI and ripening.