###### Abstract
12
Footnote 13: Current affiliation: Horticulture Research Institute, Department of Agriculture, Chhatuchak, Bangkok 10900, Thailand. 14
Footnote 14: These authors contributed equally to this work. 1
Footnote 15: Current affiliation: Horticulture Research Institute, Department of Agriculture, Chhatuchak, Bangkok 10900, Thailand. 17
Footnote 17: These authors contributed equally to this work. 1  
Due to the crucial roles of carotenoids in plants and humans, the carotenoid metabolic pathway has been well studied in a number of fruits and vegetables, such as citrus, melon, strawberry, apple, and chili [3; 4; 5; 6; 7; 8]. As shown in Figure 1, C\({}_{20}\)-geranylgeranyl diphosphate (GGPP) is used as a substrate in the carotenoid biosynthesis pathway and then catalyzed by phytoene synthase (PSY) to produce colorless C40-phytoene. A subsequent series of desaturation and isomerization results in the conversion, catalyzed by phytoene desaturase (PDS), \(\zeta\)-carotene desaturase (ZDS), and carotenoid isomerase (CRTISO). Then, the two critical branching steps are carried forward to yield diverse carotenoids. The cyclization of lycopene with one \(\epsilon\)-ring and one \(\beta\)-ring produces \(\alpha\)-carotene by lycopene \(\epsilon\)-cyclase (LCYe) and lycopene \(\beta\)-cyclase (LCYb). \(\alpha\)-Carotene is subsequently converted into lutein by \(\beta\)-ring hydroxylase (HYb) and \(\epsilon\)-ring hydroxylase (HYe). Another branch of lycopene is cyclized with two \(\beta\)-rings by lycopene \(\beta\)-cyclase (LCYb) to yield \(\beta\)-carotene. Then, \(\beta\)-carotene is converted into \(\beta\)-cryptoxanthin and zeaxanthin by \(\beta\)-ring hydroxylase (HYb). Zeaxanthin is then converted into violaxanthin by zeaxanthin epoxidase (ZEP). Furthermore, carotenoid catabolism can be catalyzed by a group of enzymes, called carotenoid cleavage dioxygenases (CCDs). They cleave a variety of carotenoids at different cleavage positions depending on the carotenoid substrate. The CCDs can cleave the double bonds of several carotenoid substrates to generate diverse products of apocarotonoids. 9-_cis_-epoxycarotenoid dioxygenases (NCEDs), members of the CCD family, enzymatically catabolize violaxanthin to yield C25 epoxy-apocartenoid, which is then modified to abscisic acid (ABA). The earlier studies on carotenoid metabolism demonstrated that carotenoid content and composition could be varied among fruit development stages and ripening stages, plant species/cultivars, and plant tissues [9]. In various fruits and vegetables, carotenoid content continuously increased during fruit development together with the appearance of yellow/orange color in ripe fruit, such as melon, tomato, and citrus [3; 10; 11]. Contrastingly, the carotenoid content dramatically decreased during fruit development in  
Figure 1: The principal pathway of carotenoid metabolism in higher plants. Abbreviations of carotenoid metabolic enzymes: PSY, phytoene synthase; PDS, phytoene desaturase; ZDS, \(\zeta\)-carotene desaturase; CRISO, carotenoid isomerase; LCYe, lycopene \(\epsilon\)-cyclase; LCYb, lycopene \(\beta\)-cyclase; HYe, \(\epsilon\)-ring hydroxylase; HYb, \(\beta\)-ring hydroxylase; ZEP, zeaxanthin epoxidase; CCDs, carotenoid cleavage dioxygenases; NCEDs, 9-_cis_-epoxycarotenoid dioxygenases. apple, grape, and some berry fruits due to the anthocyanin biosynthesis for red pigment formation [12; 13; 14; 15]. Carotenoid biosynthesis is a crucial biochemical change during mango fruit development and ripening. In recent years, the regulatory mechanism of carotenoid metabolism has been evaluated in a great number of fruits and vegetables during the pre/postharvest process. However, limited information is currently available on mango fruits. Therefore, the objective of this research was to elucidate carotenoid accumulation and the expression of carotenoid genes during fruit development and ripening in both the peel and pulp of three mango cultivars with different fruit colors, namely: 'Kaituk', 'Nam Dok Mai No.4', and 'Nam Dok Mai Sithong'.