Abstract
Carotenoids are responsible for the different flesh colors in watermelon fruit, such as white, salmon yellow, orange, pale yellow, canary yellow, crimson red, and scarlet red. In red-fleshed watermelons lycopene constitutes the major pigment and b-carotene the secondary. The predominant carotenoid in yellow-fleshed watermelon is neoxanthin. Lycopene content in watermelon is related to genotype and ploidy level, harvest maturity, and growth and development conditions. Watermelon flesh colors are controlled by several gene loci. There are two or three alleles identified at each gene locus. Up to now several full-length cDNAs or gene fragments encoding enzymes in the carotenoid metabolic pathway have been isolated and characterized from mature watermelon fruits. Differential expression of carotenogenic genes was examined in flesh, ovary, leaf, and root tissues across different colored fleshes (white, canary yellow, salmon yellow, orange, and red). Carotenogenic gene expression was also analyzed at three fruit developmental stages (10, 20, and 30 days postanthesis) in five flesh colors of watermelon cultivars (red, pink, orange, yellow, and white).
Highlights
Watermelon is the third most popular fruit vegetable in the world and the largest among the fruits eaten in hot weather
Bang isolated a total of eight fulllength cDNAs encoding enzymes in the carotenoid biosynthetic pathway from watermelon: phytoene synthase (PSY-A and PSY-B), phytoene desaturase (PDS), -carotene desaturase (ZDS), carotenoid isomerase (CRT-ISO), lycopene -cyclase (LCYB), -carotene hydroxyl-lase (CHYB), and zeaxanthin epoxidase (ZEP) [46]
The watermelon PSY fragment shares 97.8% identity with melon PSY, 94% with Momordica charantia PSY, and 90.3% with citrus PSY [49], but only 59.2% with PSY-A and 55.8% with PSY-B cloned by Bang [46]. cDNA fragments for PDS, ZDS, CRTISO, LCYB, and CHYB show over 90% identity with the corresponding genes reported by Bang [46]
Summary
Watermelon is the third most popular fruit vegetable in the world and the largest among the fruits eaten in hot weather. Flesh color is an important trait of watermelon. There are eight designated flesh colors in watermelon: white, salmon yellow, orange, crimson red, scarlet red, pale yellow, canary yellow and green [1]. Watermelon contains diverse carotenoids that are responsible for the different flesh colors except green flesh color. Like in other fruits and vegetables, carotenoids are main functional components and micronutrients in watermelon. Investigation of carotenoid composition and content, and its metabolic pathway in watermelon should become an important field of watermelon breeding for quality estimation and nutrition breeding
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