Carotenoid Biosynthesis in Oriental Melon (Cucumis melo L. var. makuwa)

Full-length cDNAs encoding xi-carotene desaturase (CmZDS), lycopene epsilon-cyclase (CmLCYE), beta-ring carotene hydroxylase (CmCHXB), and zeaxanthin epoxidase (CmZEP), and partial-length cDNA encoding epsilon-ring carotene hydroxylase (CmCHXE) were isolated in Chamoe (Cucumis melo L. var. makuwa), an important commercial fruit. Sequence analyses revealed that these proteins share high identity and common features with other orthologous genes. Expression levels of entire genes involved in the carotenoid biosynthetic pathway were investigated in the peel, pulp, and stalk of chamoe cultivars Ohbokggul and Gotgam. Most of the carotenoid biosynthetic genes were expressed at their highest levels in the stalk, whereas carotenoids were highly distributed in the peel. The expression levels of all carotenoid biosynthetic genes in fruits of the native cultivar Gotgam chamoe were higher than those in the cultivar Ohbokggul chamoe, consistent with the abundant carotenoid accumulation in Gotgam chamoe fruits and trace carotenoid content of Ohbokggul chamoe fruit. Lutein and beta-carotene were the dominant carotenoids; high levels (278.05 mu g g (-1) and 112.02 mu g g (-1) dry weight, respectively) were found in the peel of Gotgam chamoe. Our findings may provide a foundation for elucidating the carotenoid biosynthetic mechanism in C. melo and inform strategies for developing new chamoe cultivars with improved characteristics.