Dataset Information

Expression of a Chromoplast-Specific Lycopene ?-Cyclase Gene (CYC-B) Is Implicated in Carotenoid Accumulation and Coloration in the Loquat.

ABSTRACT: Carotenoids are the principal pigments in the loquat. Although the metabolic pathway of plant carotenoids has been extensively investigated, few studies have been explored the regulatory mechanisms of loquat carotenoids because knowledge of the loquat genome is incomplete. The chromoplast-specific lycopene ?-cyclase gene (CYC-B) could catalyze cyclization of lycopene to ?-carotene. In this study, the differential accumulation patterns of loquat with different colors were analyzed and virus-induced gene silencing (VIGS) was utilized in order to verify CYC-B gene function. Using a cloning strategy of homologous genes, a CYC-B gene orthologue was successfully identified from the loquat. At a later stage of maturation, CYC-B gene expression and carotenoids concentrations in the 'Dawuxing' variety were higher than in 'Chuannong 1-5-9', possibly leading to the difference in pulp coloration of loquat. Interference of CYC-B gene expression in the loquat demonstrated clear visual changes. The green color in negative control fruits became yellow, while TRV2-CYC-B silenced fruits remained green. CYC-B gene expression and total carotenoid content in the pulp decreased by 32.5% and 44.1%, respectively. Furthermore, multiple key genes in the carotenoid metabolic pathway synergistically responded to downregulation of CYC-B gene expression. In summary, we provide direct evidences that CYC-B gene is involved in carotenoid accumulation and coloration in the loquat.

SUBMITTER: Hong M

PROVIDER: S-EPMC6995616 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Expression of a Chromoplast-Specific Lycopene β-Cyclase Gene (CYC-B) Is Implicated in Carotenoid Accumulation and Coloration in the Loquat.

Hong Min M Chi Zhuo-Heng ZH Wang Yong-Qing YQ Tang Yue-Ming YM Deng Qun-Xian QX He Ming-Yang MY Wang Ri-Kui RK He Yi-Zhong YZ

Biomolecules 20191213 12

Carotenoids are the principal pigments in the loquat. Although the metabolic pathway of plant carotenoids has been extensively investigated, few studies have been explored the regulatory mechanisms of loquat carotenoids because knowledge of the loquat genome is incomplete. The chromoplast-specific lycopene β-cyclase gene (CYC-B) could catalyze cyclization of lycopene to β-carotene. In this study, the differential accumulation patterns of loquat with different colors were analyzed a ...[more]

PMID: 31847172

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Project description:BackgroundCarotenoids are a group of C40 isoprenoid molecules that play diverse biological and ecological roles in plants. Tomato is an important vegetable in human diet and provides the vitamin A precursor beta-carotene. Genes encoding enzymes involved in carotenoid biosynthetic pathway have been cloned. However, regulation of genes involved in carotenoid biosynthetic pathway and accumulation of specific carotenoid in chromoplasts are not well understood. One of the approaches to understand regulation of carotenoid metabolism is to characterize the promoters of genes encoding proteins involved in carotenoid metabolism. Lycopene beta-cyclase is one of the crucial enzymes in carotenoid biosynthesis pathway in plants. Its activity is required for synthesis of both alpha-and beta-carotenes that are further converted into other carotenoids such as lutein, zeaxanthin, etc. This study describes the isolation and characterization of chromoplast-specific Lycopene beta-cyclase (CYC-B) promoter from a green fruited S. habrochaites genotype EC520061.ResultsA 908 bp region upstream to the initiation codon of the Lycopene beta-cyclase gene was cloned and identified as full-length promoter. To identify promoter region necessary for regulating developmental expression of the ShCYC-B gene, the full-length promoter and its three different 5' truncated fragments were cloned upstream to the initiation codon of GUS reporter cDNA in binary vectors. These four plant transformation vectors were separately transformed in to Agrobacterium. Agrobacterium-mediated transient and stable expression systems were used to study the GUS expression driven by the full-length promoter and its 5' deletion fragments in tomato. The full-length promoter showed a basal level activity in leaves, and its expression was upregulated > 5-fold in flowers and fruits in transgenic tomato plants. Deletion of -908 to -577 bp 5' to ATG decreases the ShCYC-B promoter strength, while deletion of -908 to -437 bp 5' to ATG led to significant increase in the activity of GUS in the transgenic plants. Promoter deletion analysis led to the identification of a short promoter region (-436 bp to ATG) that exhibited a higher promoter strength but similar developmental expression pattern as compared with the full-length ShCYC-B promoter.ConclusionFunctional characterization of the full-length ShCYC-B promoter and its deletion fragments in transient expression system in fruto as well as in stable transgenic tomato revealed that the promoter is developmentally regulated and its expression is upregulated in chromoplast-rich flowers and fruits. Our study identified a short promoter region with functional activity and developmental expression pattern similar to that of the full-length ShCYC-B promoter. This 436 bp promoter region can be used in promoter::reporter fusion molecular genetic screens to identify mutants impaired in CYC-B expression, and thus can be a valuable tool in understanding carotenoid metabolism in tomato. Moreover, this short promoter region of ShCYC-B may be useful in genetic engineering of carotenoid content and other agronomic traits in tomato fruits.

Project description:Among naturally occurring pigments, carotenoids are importantly involved in the photosynthesis of plants and responsible for the coloration of petals and fruits. Osmanthus fragrans Lour., a famous ornamental plant, has many cultivars with different flower color. Petal coloration in O. fragrans mainly depends on the kinds of carotenoids and their contents. To investigate the mechanism of flower coloration in different cultivars, an analysis of phenotypic classification, phytochemistry, as well as the expression of carotenoid metabolism genes based on different groups was performed in the present study. Two main clusters including the orange-red cluster containing Aurantiacus cultivars and the yellowish-white cluster containing the other three cultivar groups were classified using the CIEL?a?b? system. No significant differences in flavonoid contents were observed between these two clusters. However, carotenoids, especially ?-carotene and ?-carotene, were found to have crucial roles in the diversity of floral coloration among the different cultivars. Carotenoid compositions in the petals of cultivars from both clusters consisted of ?-carotene, ?-carotene, ?-cryptoxanthin, ?-cryptoxanthin, lutein, and zeaxanthin, but carotenoid accumulation patterns during the flowering process were different. The petals of the yellowish-white cultivars exhibited high contents of ?-carotene, lutein and ?-carotene, whereas the petals of the orange-red cultivars mainly contained ?-carotene and ?-carotene. The profound diversity in the total carotenoid concentrations in the two clusters was determined by the transcript levels of OfCCD4. Furthermore, the accumulation of upstream products with orange color in orange-red cultivars was partially due to the low expression of OfCHYB, whereas the relatively higher OfCHYB expression in the petals of the yellowish-white cultivars led to higher proportions of lutein, which is yellow. We also found that downregulation of OfLCYE, which encodes ?-ring cyclase, indicated that the carotenoid flux of most cultivars mainly resulted in more ?, ?-branched products. Additionally, carotenoid biosynthesis in green tissues and petals was compared, revealing the tissue specificity of carotenoid accumulation in O. fragrans. Therefore, the effects of multiple genes on carotenoid accumulation give rise to the colorful O. fragrans.

Dataset Information

Expression of a Chromoplast-Specific Lycopene ?-Cyclase Gene (CYC-B) Is Implicated in Carotenoid Accumulation and Coloration in the Loquat.

Publications

Expression of a Chromoplast-Specific Lycopene β-Cyclase Gene (<i>CYC</i>-<i>B</i>) Is Implicated in Carotenoid Accumulation and Coloration in the Loquat.

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