Articles
NEW INSIGHTS INTO THE REGULATION OF CAROTENOID DIVERSITY IN CITRUS FRUITS
Article number
892_39
Pages
321 – 327
Language
English
Abstract
The relevance of carotenoid complement in citrus fruits is well recognized not only as pigments responsible for peel and pulp colouration but also by their nutraceuticals properties.
The diversity of pigmentation among the different Citrus species and mutants provides also valuables genetic tools to identify key regulatory steps of the pathway and candidate genes for future biotechnological improvement.
Genes for the different metabolic steps of the carotenoid biosynthetic pathway have been isolated and their expression analyzed in peel and pulp of different citrus fruits.
An emerging picture of the metabolic pathway is now revealing key regulatory steps, as phytoene synthase (PSY), entrance of the pathway, cyclization of lycopene, either ε- or β-lycopene cyclase (LCY), and hydroxylation of β-carotene (CHX). However, gene expression analysis not always could explain and fulfil the changes in carotenoid content and composition, indicating that we have only fragmentary view of the process and other still unknown genes and mechanism may be operating.
Differential expression of alleles with different functional activity, as those recently shown for β-lycopene cyclase (βLCY2) in oranges and red grapefruits, is an additional regulatory mechanism of carotenoid biosynthesis in citrus fruits.
Moreover, differences in the accumulation of β-cryptoxanthin between orange and mandarin fruits appears to be linked with differences in the expression of upstream carotene genes (PSY and ZDS) and downstream xanthophyll biosynthetic genes (β-CHX), indicating that relative expression profile of the genes of the pathway may also determine accumulation of specific carotenoids.
An update of the physiological and molecular mechanisms operating in the carotenoid biosynthetic pathway that may be implicated in the diversity and colour singularities of citrus fruits is presented and discussed.
The diversity of pigmentation among the different Citrus species and mutants provides also valuables genetic tools to identify key regulatory steps of the pathway and candidate genes for future biotechnological improvement.
Genes for the different metabolic steps of the carotenoid biosynthetic pathway have been isolated and their expression analyzed in peel and pulp of different citrus fruits.
An emerging picture of the metabolic pathway is now revealing key regulatory steps, as phytoene synthase (PSY), entrance of the pathway, cyclization of lycopene, either ε- or β-lycopene cyclase (LCY), and hydroxylation of β-carotene (CHX). However, gene expression analysis not always could explain and fulfil the changes in carotenoid content and composition, indicating that we have only fragmentary view of the process and other still unknown genes and mechanism may be operating.
Differential expression of alleles with different functional activity, as those recently shown for β-lycopene cyclase (βLCY2) in oranges and red grapefruits, is an additional regulatory mechanism of carotenoid biosynthesis in citrus fruits.
Moreover, differences in the accumulation of β-cryptoxanthin between orange and mandarin fruits appears to be linked with differences in the expression of upstream carotene genes (PSY and ZDS) and downstream xanthophyll biosynthetic genes (β-CHX), indicating that relative expression profile of the genes of the pathway may also determine accumulation of specific carotenoids.
An update of the physiological and molecular mechanisms operating in the carotenoid biosynthetic pathway that may be implicated in the diversity and colour singularities of citrus fruits is presented and discussed.
Authors
L. Zacarias, B. Alquezar, M.J. Rodrigo
Keywords
citrus, carotenoids, gene expression, lycopene, β-cryptoxanthin
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