Cytological and molecular characterization of carotenoid accumulation in normal and high-lycopene mutant oranges

Abstract

Ripe Cara Cara sweet orange contains 25 times as much carotenoids in flesh as Newhall sweet orange, due to high accumulation of carotenes, mainly phytoene, lycopene and phytofluene. Only yellow globular chromoplasts were observed in Newhall flesh. Distinct yellow globular and red elongated crystalline chromoplasts were found in Cara Cara but only one type of chromoplast was present in each cell. The red crystalline chromoplasts contained lycopene as a dominant carotenoid and were associated with characteristic carotenoid sequestering structures. The increased accumulation of linear carotenes in Cara Cara is not explained by differences in expression of all 18 carotenogenic genes or gene family members examined, or sequence or abundance of mRNAs from phytoene synthase (PSY) and chromoplast-specific lycopene β-cyclase (CYCB) alleles. 2-(4-Chlorophenylthio)-triethylamine hydrochloride (CPTA) enhanced lycopene accumulation and induced occurrence of red crystalline chromoplasts in cultured Newhall juice vesicles, indicating that carotenoid synthesis and accumulation can directly affect chromoplast differentiation and structure. Norflurazon (NFZ) treatment resulted in high accumulation of phytoene and phytofluene in both oranges, and the biosynthetic activity upstream of phytoene desaturase was similar in Newhall and Cara Cara. Possible mechanisms for high carotene accumulation and unique development of red crystalline chromoplasts in Cara Cara are discussed.

Quantitative trait loci and differential gene expression analyses reveal the genetic basis for negatively associated β-carotene and starch content in hexaploid sweetpotato [Ipomoea batatas (L.) Lam.]

“…The finding that major genes involved in chromoplast biogenesis, starch biosynthesis, and rate-limiting genes for carotenoid biosynthesis were located within the two QTL regions, indicated that activity surrounding chromoplast biogenesis determines the level of carotenoids accumulated and displacement of starch. Our results agree with the findings of Lu et al (2017) in sweet orange, showing that crystalline chromoplast development explained most of the accumulated carotenoids more than the actual carotenoid metabolic pathways genes. The IbOr gene (Goo et al 2015) which is located within our QTL on LG12 interacts with PSY gene on LG3 to enhance chromoplast biogenesis and carotenoid accumulation (Lu et al 2006).…”

BEL1‐LIKE HOMEODOMAIN 11 regulates chloroplast development and chlorophyll synthesis in tomato fruit

“…For example, silencing of phytoene desaturase ( PDS ) and non‐intrinsic ABC protein 7 ( lNAP7 ) genes leads to Chl degradation and decreased lycopene synthesis in mature tomatoes, due to photobleaching and chloroplast destruction (Fu et al ., ). In citrus, manipulation of the pigment content of chromoplasts affects the structure of the chromoplasts (Lu et al ., ). The number and size of plastids in tomato fruit are attributed to the levels of Chl and lycopene (Cookson et al ., ; Galpaz et al ., ).…”

Largely different carotenogenesis in two pummelo fruits with different flesh colors

“…Recently, the mechanism of red-fleshed pigmentation due to carotenoids has attracted increasing amounts of research attention, and relevant candidate genes have been verified in papaya [ 2 ], carrot [ 9 ] and tomato [ 10 ]. Recently, the composition and content of carotenoids in red-fleshed citrus were reported to largely differ from those in pale-fleshed/orange-fleshed citrus [ 11 , 12 , 13 ]. However, owing to the lack of records concerning the breeding history of some red-fleshed citrus cultivars, the naturally occurring highly hybridized genetic background and the long juvenile phase of citrus seedlings [ 14 ], the mechanism of carotenogenesis in red-fleshed citrus remains largely unknown.…”