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Carotenoids are considered to be important components in mango fruits. However, there is a lack of understanding about the regulation of carotenoids in mango. To gain an insight into the carotenoid metabolism pathway, carotenoid content and the expression of carotenoid metabolic genes were investigated in the peel and pulp of mango during fruit development and ripening in three cultivars, ‘Kaituk’, ‘Nam Dok Mai No.4′, and ‘Nam Dok Mai Sithong’, which are different in color. The highest carotenoid content was observed in ‘Kaituk’, followed by ‘Nam Dok Mai No.4′ and ‘Nam Dok Mai Sithong’, with the major carotenoid being β-carotene. The gene expression analysis found that carotenoid metabolism in mango fruit was primarily regulated at the transcriptional level. The changing patterns of carotenoid biosynthetic gene expression (MiPSY, MiPDS, MiZDS, MiCRTISO, MiLCYb, MiLCYe, MiHYb, and MiZEP) were similar to carotenoid accumulation, and ‘Kaituk’ exhibited a higher expression level than the other two cultivars. In addition, the differential regulation of carotenoid catabolic genes was found to be a mechanism responsible for variability in carotenoid content among the three mango cultivars. The expression of carotenoid catabolic genes (MiCCD1, MiNCED2, and MiNCED3) more rapidly decreased in ‘Kaituk’, resulting in a larger amount of carotenoids in ‘Kaituk’ than the other two cultivars.

The 'Siam Red Ruby' (Citrus grandis) is a new lycopene-accumulating pumelo variety, which is grown only in the Pakpanang area of the Nakhon Si Thammarat province of Thailand. In this study, we harvested 'Siam Red Ruby' fruit at five ripening stages, and the changes in the accumulation of carotenoid and carotenogenic gene expression were investigated in the pulp. During the ripening process, the contents of phytoene, ζ-Carotene, lycopene, β-carotene, β-cryptoxanthin, and all-trans-violaxanthin increased gradually, while the contents of αcarotene and lutein decreased in the pulp of 'Siam Red Ruby'. In the mature fruit of 'Siam Red Ruby', a high amount of lycopene was accumulated in the pulp, accounting for more than 93.26% of the total carotenoid content. The massive accumulation of lycopene led to an attractive red color of the 'Siam Red Ruby' pulp. In addition, gene expression results showed that the increases in the expression of upstream genes (CitPSY, CitPDS, CitZDS, CitZISO, and CitCRTISO), and decreases in the expression of genes downstream (CitLCYb1, CitLCYb2, CitLCYe, CitHYb, and CitHYe) was the main mechanism of lycopene accumulation in the pulp of 'Siam Red Ruby' pumelo.

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