Abstract

Most tropical and subtropical produce are so cold-sensitive that refrigeration reduces shelf-life and quality. Tomato (Solanum lycopersicum L.) fruit, experiences Postharvest Chilling Injury (PCI) when stored at 0-12.5°C. Symptoms include surface pitting, and uneven ripening and decay, due to metabolic and physiological dysfunction. Unlike tomato, Arabidopsis thaliana can cold-acclimate partly due to the CBF family of transcription factors (AtCBF1-3). The ectopic and constitutive overexpression of AtCBFs led to higher chilling tolerance but had negative developmental effects in tomato plants, and fruit response to cold stress was not tested. Constitutive overexpression of CBF1 from the cold-tolerant wild tomato relative Solanum habrochaites (ShCBF1) resulted in higher cold-tolerance in Arabidopsis plants. This suggests that increasing the control of transgenic CBF1 expression could be useful to study PCI in tomato fruit without detrimental effects on plant development. We hypothesize that CBF1 overexpression will increase chilling tolerance and ameliorate PCI symptoms during refrigeration. In this study, Micro-Tom tomato plants were independently transformed with three constructs: a dexamethasone system to chemically trigger AtCBF1 expression, and a stress-inducible promoter (RD29A) to induce ShCBF1 or SlCBF1 specifically when fruit are refrigerated. Fruit harvested at breaker stage were stored at 2.5 (PCI-inducing) or 12.5°C (control, non-PCI inducing) for 1- 3 weeks, and transferred to 20°C to promote PCI symptoms. To assess changes in whole-plant cold tolerance, the photosynthetic performance of lines RD29A::ShCBF1 and RD29A::SlCBF1 was measured under cold stress. Results showed that high expression of transgenic CBF1 in fruit as determined by qRT-PCR, was linked to accelerated senescence and an aggravation of PCI symptoms, both quantified by objective color (Hue angle) and surface pitting scores. Overall, this suggest that accelerated senescence during refrigeration in CBF1-overexpressed fruit could be a mechanism to ensure seed dispersal under extreme stress conditions, and that PCI may offer an evolutionary advantage in tomato.