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ISHS Acta Horticulturae 1135: III International Symposium on Citrus Biotechnology

Mechanism of -cryptoxanthin accumulation in citrus fruits

Author:   M. Kato
Keywords:   β-cryptoxanthin, carotenoid, citrus, gene expression
DOI:   10.17660/ActaHortic.2016.1135.1
Citrus fruits exhibit bright yellow or orange color in flavedo and juice sacs. These colors are mainly attributed to carotenoid accumulation. Carotenoid concentration and composition vary greatly among citrus varieties. β-Cryptoxanthin, one of the carotenoids, is a functional component for the prevention of certain lifestyle-related diseases, especially cancers. In the present study, Satsuma mandarin (variety accumulating β-cryptoxanthin predominantly), Valencia orange (variety accumulating violaxanthin predominantly), and Lisbon lemon (variety accumulating small amounts of carotenoids) were used to elucidate the β-cryptoxanthin accumulation during fruit maturation. The expression of carotenoid biosynthetic genes was investigated in the three citrus varieties. In Satsuma mandarin and Valencia orange, simultaneous increases in the expression of carotenoid biosynthetic genes led to the accumulation of β,β-xanthophyll (β-cryptoxanthin, zeaxanthin, and violaxanthin) in the flavedo and juice sacs. The expression levels of the carotenoid biosynthetic genes in Lisbon lemon were lower than those in Satsuma mandarin and Valencia orange. The results indicated that the carotenoid accumulation in citrus fruits was highly regulated by the coordination of the expression among carotenoid biosynthetic genes. During the marked accumulation of β,β-xanthophylls in the juice sacs, the expression of the upstream genes (CitPSY, CitPDS, CitZDS, and CitLCYb) in Satsuma mandarin was higher than that in Valencia orange, whereas the expression of the downstream genes (CitHYb and CitZEP) in Satsuma mandarin was lower than that in Valencia orange. The results suggested that the expression balance between the upstream genes and the downstream genes was important to determine the ratio of β-cryptoxanthin/violaxanthin. Furthermore, possible factors (light, plant hormones, and sugars), which regulate β-cryptoxanthin accumulation in the juice sacs of Satsuma mandarin were investigated. These factors affected the expression of the carotenoid biosynthetic genes and the β-cryptoxanthin accumulation. Therefore, this study provides information on how carotenoid accumulation is regulated, which may produce new strategies to enhance β-cryptoxanthin production in citrus.

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