A novel carotenoid cleavage activity involved in the biosynthesis of Citrus fruit-specific apocarotenoid pigments

Abstract

Citrus is the first tree crop in terms of fruit production. The colour of Citrus fruit is one of the main quality attributes, caused by the accumulation of carotenoids and their derivative C30 apocarotenoids, mainly β-citraurin (3-hydroxy-β-apo-8′-carotenal), which provide an attractive orange-reddish tint to the peel of oranges and mandarins. Though carotenoid biosynthesis and its regulation have been extensively studied in Citrus fruits, little is known about the formation of C30 apocarotenoids. The aim of this study was to the identify carotenoid cleavage enzyme(s) [CCD(s)] involved in the peel-specific C30 apocarotenoids. In silico data mining revealed a new family of five CCD4-type genes in Citrus. One gene of this family, CCD4b1, was expressed in reproductive and vegetative tissues of different Citrus species in a pattern correlating with the accumulation of C30 apocarotenoids. Moreover, developmental processes and treatments which alter Citrus fruit peel pigmentation led to changes of β-citraurin content and CCD4b1 transcript levels. These results point to the involvement of CCD4b1 in β-citraurin formation and indicate that the accumulation of this compound is determined by the availability of the presumed precursors zeaxanthin and β-cryptoxanthin. Functional analysis of CCD4b1 by in vitro assays unequivocally demonstrated the asymmetric cleavage activity at the 7′,8′ double bond in zeaxanthin and β-cryptoxanthin, confirming its role in C30 apocarotenoid biosynthesis. Thus, a novel plant carotenoid cleavage activity targeting the 7′,8′ double bond of cyclic C40 carotenoids has been identified. These results suggest that the presented enzyme is responsible for the biosynthesis of C30 apocarotenoids in Citrus which are key pigments in fruit coloration.

Degreening Buah Jeruk Siam (Citrus nobilis) pada Beberapa Konsentrasi dan Durasi Pemaparan Etilen

“…Pada jeruk Ponkan akumulasi β-cryptoxanthin dan β-citraurin pada kulit buah menghasilkan warna jingga sedangkan violaxanthin menghasilkan warna kuning (Zhou et al, 2010). Perubahan warna kulit jeruk menjadi jingga disebabkan karena terjadinya sintesis karotenoid yang bersifat nonphotosintectic yaitu β-citraurin yang merupakan pembentuk warna jingga kemerahan pada kulit jeruk mandarin, akumulasi senyawa ini ditentukan oleh ketersediaan prekusor berupa karotenoid yang bersifat photosintetic seperti zeaxanthin dan β-cryptoxanthin (Kato et al, 2004;Rodrigo et al, 2013;Ma et al, 2013). …”

Carotene Hydroxylase Activity Determines the Levels of Both α-Carotene and Total Carotenoids in Orange Carrots

“…The levels of these xanthophylls increased only slightly, and total xanthophyll levels remained at as low levels as in nontransformed CRC control plants. This suggests increased xanthophyll turnover through their enhanced cleavage by carotenoid cleavage oxygenases (Simkin et al, 2004;Rodrigo et al, 2013). In fact, several carotenoid-derived cleavage products are important signaling molecules involved in developmental processes (strigolactones) and mediate responses toward abiotic stress (ABA; Walter and Strack, 2011;Alder et al, 2012).…”

Novel carotenoid cleavage dioxygenase catalyzes the first dedicated step in saffron crocin biosynthesis

“…Enzymes of the CCD1 family cleave a wide spectrum of different carotenoids at several different positions (9,10; 9,10,9′,10′; 5,6,5′,6′; or 7,8,7′,8′) (11,12). CCD4 enzymes cleave carotenoids at the 9′,10′ or the 7′,8′ positions and determine the level of pigmentation in plant tissues, including Chrysanthemum petals (13), peach flesh (14), potato tubers (15), Citrus peel (16,17), and Arabidopsis seeds (18).…”