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The floral color phenotypes of Osmanthus fragrans cultivars range from light yellow to orange yellow, with ‘Yanzhi Hong’ being the only reported cultivar with a red color. However, the underlying reason for this unique floral coloration remains unclear. The study conducted targeted metabolomics and transcriptomics analyses on the petals of ‘Yanzhi Hong’ at both initial and peak flowering stages. Candidate gene expression was validated, and expression levels of the petals of three cultivars were compared using RT-qPCR. The results revealed the presence of 27 components in the petals of ‘Yanzhi Hong’, including 5 carotenoids, 8 xanthophylls, and 14 xanthophyll esters. Notably, lycopene was detected in abundance for the first time in O. fragrans cultivars. Carotenes accounted for 78.82 ± 3.17% and 91.19 ± 1.69% of the total carotenoid content in petals during the initial and peak flowering stages, respectively, with all carotene contents increasing during the peak flowering period. β-carotene, lycopene, and γ-carotene were identified as the top three carotene components in petals during both initial and full flowering stages. The unique blush red color of ‘Yanzhi Hong’ petals could be attributed to the low content of α-carotene and the rich accumulation of lycopene. Furthermore, a total of 1550 differentially expressed genes (DEGs) were identified in petals at the peak flowering stage relative to the initial flowering stage, with 1003 genes being downregulated and 547 genes being upregulated during the full flowering stage. There are 926 differentially expressed genes (DEGs) annotated in the Gene Ontology (GO) database. Among these DEGs, those that were downregulated and upregulated during the peak flowering period showed significant enrichment in carbohydrate metabolism and oxidation–reduction processes, respectively. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis identified 14 structural genes associated with phenylpropanoid biosynthesis and 7 structural genes linked to carotenoid biosynthesis. Expression levels of candidate genes involved in carotenoid biosynthesis were examined in the petals of three cultivars (‘Yanzhi Hong’, ‘Liuye Jingui’, and ‘Gecheng Dangui’) at both the initial and peak flowering stages. The results indicated that the decreased expression of LYG009054 (LYCE) and LYG018651 (LYCB) in ‘Yanzhi Hong’ resulted in higher lycopene accumulation and lower α-carotene content in the petals. This study offers valuable insights into the mechanisms underlying the unique flower color phenotype of O. fragrans, proving a basis for further research on carotenoid metabolism pathways and the breeding of new cultivars with a variety of flower colors in O. fragrans.

Histone acetylation and methylation, governed by various histone modification (HM) gene families, are vital for plant biological processes. However, there are limited studies that have explored HMs in ornamental horticultural trees, including sweet osmanthus (Osmanthus fragrans). We performed genome-wide search and identified 208 OfHMs, encompassing 81 histone methyltransferases (OfHMTs), 51 histone demethylases (OfHDMs), 49 histone acetyltransferases (OfHATs) and 27 histone deacetylases (HDACs). Our comprehensive analysis covered chromosome locations, gene structures, conserved domains, cis-acting elements, phylogenetic comparisons, protein interaction networks and functional enrichment pathways for these gene families. Additionally, tandem and fragment replications were unveiled as contributors to the expansion of OfHMs, with some genes exhibiting positive selection. Furthermore, we examined OfHM expression profiles across various tissues and flowering stages, and under 5′-azacytidine (Aza) and ethylene treatments. Most OfHMs displayed heightened expression in leaves, and were downregulated during the flower opening and senescence stages, including OfPRMTs, OfHDTs, OfHDAs, OfSRTs, OfJMJs and OfHAGs; 75.86% and 80.77% of the differentially expressed OfHMs were upregulated after Aza and ethylene treatments, including OfHAGs, OfHDAs and OfSDGs. This study offers a comprehensive analysis of the OfHM gene family, which indicated their potential involvement in ethylene and Aza responses, and in the flowering process. These findings provide valuable insights into the role of OfHMs in flowering and stress responses.

According to the coexistence theory of slag structure, a calculation model for the activity of FeO in the quaternary system SiO2-CaO-Al2O3-FeO of depleted copper slag was established. The model was used to calculate and analyze the effects of temperature (T), basicity (B), and Al2O3 content on the activity of FeO (NFeO). The results show that temperature has little impact on NFeO. With increased basicity, NFeO first increased slightly, then increased sharply, and finally decreased. It is easier for CaO to combine with SiO2 than FeO to form calcium silicate, which replaces FeO in 2FeO·SiO2 and increases NFeO. However, when basicity is higher than 2.0, CaO not only reacts with SiO2, but also combines with FeO to form calcium ferrate compounds to decrease NFeO. In addition, the activity of FeO decreases with increased Al2O3 content because of the reaction between CaO and Al2O3. The results can be used as a theoretical basis to guide the carbothermal reduction process of copper slag.