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.

Floral scent is an important part of volatile organic compounds (VOCs) emitted from plants, and is influenced by many environmental and endogenous factors. To investigate the influence of temperature on the emission of the floral scent of Osmanthus fragrans, the number of chemical compounds and their relative release amounts from four cultivars of O. fragrans under different temperature treatments, were identified using the solid-phase microextraction (SPME) technique and gas chromatography-mass spectrometry (GC-MS) in this study. Results revealed that the numbers and release amounts of floral scent components were significantly influenced by different temperatures, and depend on different cultivars and different types of compounds. Overall, most cultivars had the largest number of chemical compounds in 19 °C and the numbers of chemical compounds decreased with the increase or decrease in the temperature. Alcohols and ketones were the two main kinds of compounds responding to temperature change. The response of a specific chemical compound to temperature change was different in four cultivars. Generally, linalool, α-ionone, β-ionone, and γ-decalactone accounted for the highest proportion in the nine main compounds, and changes of these four chemical compounds to different temperatures had obvious contributions to the floral scent of O. fragrans. The results obtained provide evidence that temperatures can greatly influence the emission of floral scent.

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Background Osmanthus fragrans (Oleaceae) is one of the most important ornamental plant species in China. Many cultivars with different leaf color phenotypes and good ornamental value have recently been developed. For example, a new cultivar ‘Qiannan Guifei’, presents a rich variety of leaf colors, which change from red to yellow-green and ultimately to green as leaves develop, making this cultivar valuable for landscaping. However, the biochemical characteristics and molecular mechanisms underlying leaf color changes of these phenotypes have not been elucidated. It has been hypothesized that the biosynthesis of different pigments in O. fragrans might change during leaf coloration. Here, we analyzed transcriptional changes in genes involved in chlorophyll (Chl), flavonoid, and carotenoid metabolic pathways and identified candidate genes responsible for leaf coloration in the new cultivar ‘Qiannan Guifei’. Methods Leaf samples were collected from ‘Qiannan Guifei’ plants at the red (R), yellow-green (YG) and green (G) leaf stages. We compared the different-colored leaves via leaf pigment concentrations, chloroplast ultrastructure, and transcriptomic data. We further analyzed differentially expressed genes (DEGs) involved in the Chl, flavonoid, and carotenoid metabolic pathways. In addition, we used qRT-PCR to validate expression patterns of the DEGs at the three stages. Results We found that, compared with those at the G stage, chloroplasts at the R and YG stages were less abundant and presented abnormal morphologies. Pigment analyses revealed that the leaves had higher flavonoid and anthocyanin levels at the R stage but lower Chl and carotenoid concentrations. Similarly, Chl and carotenoid concentrations were lower at the YG stage than at the G stage. By using transcriptomic sequencing, we further identified 61 DEGs involved in the three pigment metabolic pathways. Among these DEGs, seven structural genes (OfCHS, OfCHI, OfF3H, OfDFR, OfANS, OfUGT andOf3AT) involved in the flavonoid biosynthesis pathway were expressed at the highest level at the R stage, thereby increasing the biosynthesis of flavonoids, especially anthocyanins. Six putativeOfMYB genes, including three flavonoid-related activators and three repressors, were also highly expressed at the R stage, suggesting that they might coordinately regulate the accumulation of flavonoids, including anthocyanins. Additionally, expressions of the Chl biosynthesis-related genes OfHEMA, OfCHLG and OfCAO and the carotenoid biosynthesis-related genes OfHYB and OfZEP were upregulated from the R stage to the G stage, which increased the accumulation of Chl and carotenoids throughout leaf development. In summary, we screened the candidate genes responsible for the leaf color changes of ‘Qiannan Guifei’, improved current understanding of the regulatory mechanisms underlying leaf coloration and provided potential targets for future leaf color improvement in O. fragrans.