Carotenoid Accumulation and Its Contribution to Flower Coloration of Osmanthus fragrans

Abstract

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 α-carotene and β-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 α-carotene, β-carotene, α-cryptoxanthin, β-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 β-carotene, lutein and α-carotene, whereas the petals of the orange-red cultivars mainly contained β-carotene and α-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 𝜀-ring cyclase, indicated that the carotenoid flux of most cultivars mainly resulted in more β, β-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.

Comparative Proteomic Analysis by iTRAQ Reveals that Plastid Pigment Metabolism Contributes to Leaf Color Changes in Tobacco (Nicotiana tabacum) during Curing

“…Chlorophyll was found to be the most abundant plastid pigment in tobacco leaves at 0 h, but the ratio of carotenoid/chlorophyll of different samples was all larger than or equal to 1.30 during 48-72 h. In addition, the ratios between xanthophylls and β-carotene of different samples were all larger than or equal to 1.71 during 0-72 h. Thus, the tobacco leaves showed a green phenotype at 0 h and a yellow phenotype at 48 h and 72 h. Pigment metabolism and their relative contents were responsible for the formation of the yellow phenotype, which was consistent with previous reports [11,30,39]. The data were expressed as the color values of lightness L*, greenness a*, and yellowness b* [2,11,27]. In this study, the change in color was quantified as the increment in the values of L*, a*, and b*, which is associated with the pigment degradation and the increase in the relative concentrations of the carotenoid and the phenotypic change in tobacco leaves during curing.…”

“…Color change in plants is determined by the content of various plastid pigments, and plant organs are intensely yellow due to the accumulation of the xanthophylls, including lutein, neoxanthin, and violaxanthin [11,25,26]. The green color changes to orange due to the breakdown of chlorophylls and the accumulation of the β-carotene in plants [6,25].…”

“…The carotenoids represent the most widespread group of pigments in nature, with over 750 members and an estimated yield of 100 million tons per year [6][7][8], and many carotenoid compounds have been examined, such as β-carotene, lutein, violaxanthin, and neoxanthin [9][10][11]. Certain plant proteins, such as carotenoid cleavage dioxygenases (CCDs) and violaxanthin de-epoxidase (VDE), significantly participate in the regulation of the carotenoid and degradation products content in plants [6,10,12].…”

“…Parameters of the CIEL*a*b color coordinate include lightness L* (positive white and negative black), and two chromatic components a* (positive red and negative green) and b* (positive yellow and negative blue) [2,11]. Color change is one of the most dramatic events occurring in plant postharvest organs during curing and storage [2,5,23].…”

“…The green color changes to orange and red due to the breakdown of chlorophylls and the accumulation of the orange β-carotene and the red lycopene in plants [6,25]. The plants seem intensely yellow due to the accumulation of the xanthophylls, namely lutein, neoxanthin, and violaxanthin [11,25,26]. The color change is determined by a dynamic shift in pigment composition and their contents in plants, which is associated with the regulation of differentially expressed proteins (DEPs).…”