BACKGROUND Previous reports have mainly focused on the volatiles in citrus fruits, and there have been few reports about the volatiles in citrus leaves and flowers. However, citrus leaves and flowers are also rich in volatile compounds with unique aromas. Here, to investigate the volatiles in citrus leaves and flowers, volatile profiling was performed on leaves from 62 germplasms and flowers from 25 germplasms. RESULTS In total, 196 and 82 volatile compounds were identified from leaves of 62 citrus germplasms and flowers of 25 citrus germplasms, respectively. The dominant volatile terpenoids were more diverse in citrus leaves than in peels. A total of 34 volatile terpenoids were commonly detected in the leaves of at least 20 germplasms, among which 31 were overaccumulated in the leaves of wild or semiwild germplasms. This result was consistent with the high expression levels of five genes and one key gene of the mevalonate and 2-C-methyl-D-erythritol-4-phosphate (MEP) biosynthetic pathways, respectively, as well as the low expression levels of geranylgeranyl diphosphate synthase of the MEP pathway, relative to the levels in cultivars. Fully open flowers showed increased levels of four terpene alcohols and a decrease in sabinene content compared with balloon-stage flowers, especially in sweet orange. A monoterpene synthase gene was identified and functionally characterized as a sabinene synthase in vitro. CONCLUSIONS Collectively, our results suggest that 31 important terpenoids are abundant in wild or semiwild citrus germplasms, possibly because of a negative effect of domestication on the volatiles in citrus leaves. The sweet smell of fully open flowers may be attributed to increased levels of four terpene alcohols. In addition, a sabinene synthase gene was identified by combined transcriptomic and metabolomic analyses.

中文翻译：

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转录组学和代谢组学分析提供了对柑橘叶片和花朵的挥发性化合物的了解。

背景技术以前的报道主要集中在柑桔类水果中的挥发物，关于柑桔类叶和花中的挥发物的报道很少。但是，柑橘叶和花朵也富含具有独特香气的挥发性化合物。在这里，为了研究柑橘叶片和花朵中的挥发物，对来自62个种质的叶子和来自25个种质的花朵进行了挥发性分析。结果总共从62种柑橘种质的叶片和25种柑橘种质的花中鉴定出196种和82种挥发性化合物。柑橘叶片中的主要挥发性萜类化合物比果皮中的多样化。通常在至少20个种质的叶片中共检测到34种挥发性萜类化合物，其中31种在野生或半野生种质的叶片中过量积累。该结果与甲羟戊酸和2-C-甲基-D-赤藓糖-4-磷酸（MEP）生物合成途径的五个基因和一个关键基因的高表达水平以及香叶基香叶基的低表达水平相一致。 MEP途径中的二磷酸合酶，相对于品种的水平。与气球期花朵相比，完全开放的花朵显示四种萜烯醇的含量增加，且bin烯含量降低，尤其是甜橙。鉴定了单萜合酶基因，并在体外功能上将其表征为sa烯合酶。结论总体而言，我们的研究结果表明，野生或半野生柑橘种质中都富含31种重要的萜类化合物，这可能是由于驯化对柑橘叶片中的挥发物具有负面影响。完全开放的花朵的甜味可能归因于四种萜烯醇含量的增加。另外，通过组合的转录组学和代谢组学分析鉴定了sa烯合酶基因。