Exploring the differential mechanisms of carotenoid biosynthesis in the yellow peel and red flesh of papaya.

Red-fleshed papaya is a good material to study the different carotenoids accumulation mechanism in the peel and flesh. Although the peel and flesh of papaya closely integrated into one body, the flesh coloration changing from white to red, while the exocarp coloration changing from green to yellow. In this study, the major carotenoids accumulation and the expression patterns of key carotenoid biosynthesis pathway genes in the process of papaya fruit ripening were studied, and the carotenoid biosynthetic pathways in the yellow peel and red flesh of papaya were investigated. The carotenoid composition in papaya flesh and peel were different. The major carotenoids were lutein and β-carotene in the peel, while lycopene in the flesh. The accumulation of carotenoids, including lycopene, β-carotene, and β-cryptoxanthin were considered to cause the orange-red color of papaya cv. 'Daqing No.10' flesh. The color of peel changed from green to yellow because of the fast degradation of chlorophyll and the appearance of carotenoids such as lutein and β-carotene. Thirteen genes that encode enzymes in the carotenoid biosynthetic pathway were detected in papaya fruit transcriptome: two phytoene synthase (PSY1, PSY2), two phytoene desaturase (PDS1, PDS2), one ζ-carotene desaturase (ZDS), four lycopene cyclase (CYCB, LCYB1, LCYB2, LCYE), one β-carotene hydroxylase (CHYB), one carotene ε-monooxygenase (LUT1), one violaxanthin de-epoxidase (VDE), and one zeaxanthin epoxidase (ZEP). The results of RNA-Seq and RT-qPCR showed the expression of carotenoid biosynthetic pathway genes was consistent with the change of carotenoid content. Carotenoid biosynthetic pathways in the yellow peel and red flesh of papaya were analysed based on the major carotenoids accumulation and the expression patterns of key carotenoid biosynthesis pathway genes. There was only a β-branch of carotenoid biosynthesis in the flesh of papaya, while there were both α- and β-branch of carotenoid biosynthesis in papaya peel. In the process of papaya fruit ripening, the α-branch was inhibited and the β-branch was enhanced in the peel. The differential carotenoid accumulation and biosynthesis pathway genes expression in peel and flesh, lay a foundation for further study and provide further insights to control fruit color and improve fruit quality and appearance.

Shen YH ，Yang FY ，Lu BG ，Zhao WW ，Jiang T ，Feng L ，Chen XJ ，Ming R ... -  《BMC GENOMICS》

Metabolic and transcriptional elucidation of the carotenoid biosynthesis pathway in peel and flesh tissue of loquat fruit during on-tree development.

Hadjipieri M ，Georgiadou EC ，Marin A ，Diaz-Mula HM ，Goulas V ，Fotopoulos V ，Tomás-Barberán FA ，Manganaris GA ... -  《BMC PLANT BIOLOGY》

Biochemical and molecular analysis of carotenoid biosynthesis in flavedo of orange (Citrus sinensis L.) during fruit development and maturation.

Rodrigo MJ ，Marcos JF ，Zacarías L 《JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY》

Carotenoid metabolism during bilberry (Vaccinium myrtillus L.) fruit development under different light conditions is regulated by biosynthesis and degradation.

Karppinen K ，Zoratti L ，Sarala M ，Carvalho E ，Hirsimäki J ，Mentula H ，Martens S ，Häggman H ，Jaakola L ... -  《BMC PLANT BIOLOGY》

Expression of carotenoid biosynthesis genes during carrot root development.

Carotenogenesis has been extensively studied in fruits and flower petals. Transcriptional regulation is thought to be the major factor in carotenoid accumulation in these organs. However, little is known about regulation in root organs. The root carotenoid content of carrot germplasm varies widely. The present study was conducted to investigate transcriptional regulation of carotenoid biosynthesis genes in relation to carotenoid accumulation during early carrot root development and up to 3 months after sowing. HPLC carotenoid content analysis and quantitative RT-PCR were compared to quantify the expression of eight genes encoding carotenoid biosynthesis enzymes during the development of white, yellow, orange, and red carrot roots. The genes chosen encode phytoene synthase (PSY1 and PSY2), phytoene desaturase (PDS), zeta-carotene desaturase (ZDS1 and ZDS2), lycopene epsilon-cyclase (LCYE), lycopene beta-cyclase (LCYB1), and zeaxanthin epoxidase (ZEP). All eight genes were expressed in the white cultivar even though it did not contain carotenoids. By contrast with fruit maturation, the expression of carotenogenic genes began during the early stages of development and then progressively increased for most of these genes during root development as the total carotenoid level increased in coloured carrots. The high expression of genes encoding LCYE and ZDS noted in yellow and red cultivars, respectively, might be consistent with the accumulation of lutein and lycopene, respectively. The results showed that the accumulation of total carotenoids during development and the accumulation of major carotenoids in the red and yellow cultivars might partially be explained by the transcriptional level of genes directing the carotenoid biosynthesis pathway.

Clotault J ，Peltier D ，Berruyer R ，Thomas M ，Briard M ，Geoffriau E ... -  《-》