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        不同文心兰品种香气组分差异及特征酯类合成候选基因分析

        Analysis of aroma component differences among different Oncidium cultivars and candidate genes for characteristic ester synthesis

          摘要
        • 摘要:
          目的 明确6个文心兰品种花香挥发性成分组成差异，挖掘调控特征香气物质合成的关键候选基因，解析近缘品种香气分化的代谢与分子基础。
          方法 以‘黄梦香’‘白梦香’‘海伦’‘红樱桃’‘香水564’与‘香水文心兰’等6个品种为试验材料，采用固相微萃取–气相色谱–质谱（SPME–GC–MS）技术鉴定花香挥发物组分，结合主成分分析（PCA）与层次聚类分析（HCA）解析品种间香气特征差异；对遗传亲缘关系相近的‘黄梦香’与‘白梦香’开展转录组测序，并进行代谢–基因联合关联分析。
          结果 6个文心兰品种共鉴定出113种花香挥发性成分，主要包括萜烯类、酯类和醇类，其中萜烯类相对含量为50.76%~84.13%，不同品种间挥发物组成与含量差异显著；PCA与HCA分析显示，‘黄梦香’与‘白梦香’的香气组成相似度最高，与其遗传亲缘特征相吻合。两品种共筛选获得10种显著差异挥发物，‘黄梦香’显著富集酯类物质，尤以(E)-2-甲基巴豆酸异戊酯积累突出，‘白梦香’则以单萜类物质为主，呈现明显的代谢分流特征。转录组测序共鉴定到9104个差异表达基因，代谢–基因关联分析筛选出TRINITY_DN114613_c1_g2（BCKDH-E1β亚基）为调控特征酯类合成的关键候选基因，该基因可通过异亮氨酸降解通路生成惕各酰辅酶A前体，正向促进(E)-2-甲基巴豆酸异戊酯的积累。
          结论 研究明确了6个文心兰品种的香气轮廓与品种特异性特征，揭示了同父母本近缘品种香气分化的代谢规律与分子线索，可为文心兰花香种质选育与香气品质定向改良提供理论参考。

           

          Abstract:
          Objective To clarify the differences in floral volatile components among six Oncidium cultivars and explore key candidate genes regulating the synthesis of characteristic aroma substances, and to reveal the metabolic and molecular basis of aroma differentiation in closely related cultivars.
          Method Six Oncidium cultivars, including Oncidium Twinkle 'Chian-Tzy Golden', Oncidium Twinkle 'Fragrance Fantasy', × Oncidopsis Bartley Schwarz (Beall) 'Highland' (AM/AOS), Oncidium Hwuluduen Nova 'Red Cherry', Oncidium Jairak Fragrance #564 and Oncidium Sharry Baby 'Tricolor' were used as experimental materials. Solid phase microextraction coupled with gas chromatography-mass spectrometry (SPME-GC-MS) was applied to identify floral volatile components. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used to compare aromatic characteristics among cultivars. Transcriptome sequencing and metabolome-gene association analysis were further performed on the closely related cultivars Oncidium Twinkle 'Chian-Tzy Golden' and Oncidium Twinkle 'Fragrance Fantasy'.
          Result A total of 113 floral volatile compounds were identified from six Oncidium cultivars, mainly consisting of terpenes, esters and alcohols. The relative content of terpenes ranged from 50.76% to 84.13%, and significant differences in composition and content were observed among cultivars. PCA and HCA results showed that Oncidium Twinkle 'Chian-Tzy Golden' and Oncidium Twinkle 'Fragrance Fantasy' shared the most similar aroma composition, which was consistent with their genetic relationship. Ten significantly differential volatile compounds were detected between the two cultivars. Oncidium Twinkle 'Chian-Tzy Golden' accumulated abundant esters, especially isoamyl (E)-2-methylcrotonate, while Oncidium Twinkle 'Fragrance Fantasy' was enriched in monoterpenes, showing obvious metabolic divergence. A total of 9104 differentially expressed genes were obtained by transcriptome sequencing. Metabolome-gene association analysis identified TRINITY_DN114613_c1_g2 (BCKDH-E1β subunit) as a key candidate gene for characteristic ester synthesis, which provides tiglyl-CoA precursors through the isoleucine degradation pathway and positively regulates the accumulation of isoamyl (E)-2-methylcrotonate.
          Conclusion This study clarified the aroma profiles and cultivar specificity of six Oncidium cultivars, and revealed the metabolic pattern and molecular clues of aroma differentiation in closely related sibling cultivars. The findings provide a theoretical reference for germplasm selection and targeted improvement of floral scent quality in Oncidium.

           

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