Expression of lycopene cyclase genes and their regulation on downstream carotenoids during fruit maturation of Guoqing No. 1 Satsuma mandarin and Cara Cara navel orange

Abstract

Lycopene β-cyclase ( LCYb) and lycopene ɛ-cyclase ( LCYe) are believed to be crucial genes to lycopene cyclization and downstream carotenoid accumulation. To illuminate the gene expression profiles and their regulation on downstream carotenoids, expression profiles of these two genes and contents of several corresponding carotenoids were determined by real-time PCR and HPLC, respectively, in relative shorter intervals during breaker and maturation stage of Guoqing No. 1 satsuma mandarin ( Citrus unshiu Marcow) and Cara Cara navel orange ( Citrus sinensis Osbeck). Data showed that the expression profiles of these two cyclase genes and their relative expression levels between the peels and the pulps at the same stage all varied with cultivars. But in general, accumulation of lutein and β-carotene experienced a similar tendency in both cultivars and were up-regulated by expression of LCYb and LCYe in spite of poor correlation in the pulps. Meanwhile, lycopene abundance was negatively correlated with the expression of LCYe as expected, but hardly correlated with LCYb in the pulps of Cara Cara navel orange, indicating that LCYe might exert a more prominent influence on lycopene cyclization and downstream carotenoids formation. Results of carotenoids accumulation suggest that the biosynthetic process of carotenoids would shift from upstream β, ɛ- or β, β-carotenoids such as lutein and β-carotene to downstream β, β-carotenoids during fruit development.