title: 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.
authors.affiliation: Instituto de Agroquímica y Tecnología de Alimentos, Consejo Superior de Investigaciones Científicas (IATA-CSIC), Av. Agustín Escardino 7, 46980 Paterna, Valencia, Spain.
authors.forename: María J
authors.initials: MJ
authors.lastname: Rodrigo
authors.forename: Berta
authors.initials: B
authors.lastname: Alquézar
authors.forename: Enriqueta
authors.initials: E
authors.lastname: Alós
authors.forename: Víctor
authors.initials: V
authors.lastname: Medina
authors.forename: Lourdes
authors.initials: L
authors.lastname: Carmona
authors.forename: Mark
authors.initials: M
authors.lastname: Bruno
authors.forename: Salim
authors.initials: S
authors.lastname: Al-Babili
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Zacarías
mesh_terms: D000595:Amino Acid Sequence; D002338:Carotenoids / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D002957:Citrus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D005030:Ethylenes / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics; D006358:Hot Temperature; D008958:Models, Molecular; D008969:Molecular Sequence Data; D005810:Multigene Family; D009928:Organ Specificity / Q000235:genetics; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012098:Reproduction / Q000187:drug effects / Q000235:genetics; D016415:Sequence Alignment
chemical_list: D005030:Ethylenes; D010940:Plant Proteins; D012333:RNA, Messenger; D002338:Carotenoids; C036216:ethylene
keywords: Apocarotenoid; Citrus; carotenoid; carotenoid cleavage dioxygenase; fruit coloration.; β-citraurin