Linalool and ionone are two important aromatic components in sweet osmanthus petals, and the regulatory mechanisms produce these two components remain unclear. In this study, we employed whole-genome methylation sequencing and ATAC-seq technology to analyze the genomic DNA methylation status and chromatin accessibility of sweet osmanthus cultivars “Zaohuang” and “Chenghong Dangui”. Results showed that the promoter region of TPS2, a key gene in the linalool synthesis pathway, was less methylated in “Chenghong Dangui” than in “Zaohuang”. The chromatin was more accessible in “Chenghong Dangui” than in the “Zaohuang” cultivar, which resulted in a much stronger expression of this gene in “Chenghong Dangui” than in “Zaohuang”. This eventually led to a high quantity of linalool and its oxides in the petals of “Chenghong Dangui”, but there were lower levels present in the petals of “Zaohuang”. These results suggest that DNA methylation and chromatin accessibility play major roles in linalool synthesis in sweet osmanthus. The methylation level of the promoter region of CCD4, a key gene for ionone synthesis, was higher in “Zaohuang” than that in “Chenghong Dangui”. The chromatin accessibility was lower in “Zaohuang” than in “Chenghong Dangui”, although the expression of this gene was significantly higher in “Zaohuang” than in “Chenghong Dangui”. ChIP-seq analysis and a series of experiments showed that the differential expression of CCD4 and CCD1 in the two cultivars may predominantly be the result of regulation by ERF2 and other transcription factors. However, a 183 bp deletion involving the CCD4 promoter region in “Chenghong Dangui” may be the main reason for the low expression of this gene in the petals of “Chenghong Dangui”. This study provides an important theoretical basis for improving selective breeding of key floral fragrance components in sweet osmanthus.

中文翻译：

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桂花的比较甲基组学和染色质可及性分析揭示了基因转录的调控和关键花香产生的机制

芳樟醇和紫罗兰酮是桂花花瓣中两种重要的芳香成分，产生这两种成分的调控机制尚不清楚。本研究采用全基因组甲基化测序和ATAC-seq技术对桂花品种“枣黄”和“呈红丹桂”的基因组DNA甲基化状态和染色质可及性进行分析。结果表明，芳樟醇合成途径中的关键基因TPS2的启动子区域在“呈红丹桂”中的甲基化程度低于“枣黄”。“呈红丹桂”的染色质比“枣黄”品种更容易接近，导致该基因在“呈红丹桂”中的表达比“枣黄”强得多。这最终导致“呈红丹桂”的花瓣中存在大量芳樟醇及其氧化物，但“枣皇”花瓣中含量较低。这些结果表明，DNA甲基化和染色质可及性在桂花芳樟醇合成中起主要作用。紫罗兰酮合成关键基因CCD4启动子区甲基化水平在“枣黄”中高于“呈红丹桂”。“枣黄”的染色质可及性低于“承红丹桂”，但该基因在“枣皇”中的表达明显高于“承红丹桂”。ChIP-seq分析和一系列实验表明，CCD4和CCD1在两个品种中的差异表达可能主要是ERF2等转录因子调控的结果。然而，“呈红丹桂”中CCD4启动子区183bp的缺失可能是该基因在“呈红丹桂”花瓣中低表达的主要原因。该研究为改进桂花关键花香成分选育提供了重要的理论依据。