Carotenoid gene expression and metabolic changes in the pericarp of Mandarin ‘Shatangju’ under net shed shading during growth

Fruit colour is mostly determined by the composition and content of carotenoids . In this study, a metabolic transcription analysis of carotenoids in the pericarp of ‘Shatangju’ at three different growth periods under two cultivation methods, open-air and netting, was performed. The results showed that the lightness value, red-green value and yellow-blue value indices of the pericarp varied greatly. Fourteen carotenoids were detected in the citrus pericarp. The content of lycopene was 3.21 μg/g and 3.43 μg/g, and the content of β-citraurin was 6 μg/g and 7.27 μg/g under open-air and net shed cultivation, respectively. Shading affected the synthesis of key genes such as phytoene synthase ( PSY ), carotenoid cleavage dioxygenase 4 ( CCD4 ), and zeaxanthin epoxidase ( ZEP ), thereby inhibiting the accumulation of lycopene and β-citraurin. Studies have shown that the degreening of the ‘Shatangju’ pericarp was accelerated, but the accumulation of carotenoid biosynthesis genes was inhibited, which was not conducive to the synthesis of carotenoids.