Functional Validation of Phytoene Synthase and Lycopene ε-Cyclase Genes for High Lycopene Content in Autumn Olive Fruit ().

Lycopene is the most potent antioxidant among all carotenoids and is beneficial to human health. A ripe fruit of autumn olive ( Thunb.) accumulates a high level of lycopene, which is 5-20 times higher than that in an ordinary tomato fruit. During fruit ripening of autumn olive, only phytoene synthase () expression pattern shows a tight positive correlation with the increased lycopene content observed at four ripening stages, while the lycopene ε-cyclase () transcript could not be detected throughout fruit ripening. Here, we investigated whether the two genes are important targets for engineering lycopene biosynthesis. The full-length cDNAs of and were first isolated. Fruit-specific overexpression of in tomato fruits resulted in elevated contents of lycopene and β-carotene through feedforward regulation of carotenogenic genes, i.e., downregulation of and upregulation of and . These fruits were decreased in ethylene production throughout ripening. Transcript levels of genes for system-2 ethylene synthesis (2, 4, 1, and 3), perception (3 and 4), and response (4 and 8) were also inhibited in -overexpressing fruits. Repressing ethylene synthesis and signaling transduction delayed fruit climacteric ripening of transgenic tomato plants. Additionally, RNAi suppression of enhanced β-carotene but not lycopene accumulation through altered expression of carotenogenic genes in transgenic tomato fruits by both feedforward and feedback regulatory mechanisms. Ethylene production in -RNAi fruits decreased, thereby delaying fruit ripening. Collectively, these results confirmed that transcriptional regulation of and plays a crucial role and a part in massive lycopene accumulation in autumn olive fruits, respectively. overexpression enhanced lycopene accumulation in tomato fruits independently of the ethylene pathway but did not influence the size and weight of tomato fruits. can be used as an effective strategy capable of elevating the lycopene content in fruits for improving quality.