Sweet basil (Ocimum basilicum) plants produce its characteristic phenylpropene-rich essential oil in specialized structures known as peltate glandular trichomes (PGTs). Eugenol and chavicol are the major phenylpropenes produced by sweet basil varieties whose synthetic pathways are not fully elucidated. Eugenol is derived from coniferyl acetate by a reaction catalysed by eugenol synthase. An acyltransferase is proposed to convert coniferyl alcohol to coniferyl acetate which is the first committed step towards eugenol synthesis. Here, we perform a comparative next-generation transcriptome sequencing of different tissues of sweet basil, namely PGT, leaf, leaf stripped of PGTs (leaf–PGT), and roots, to identify differentially expressed transcripts specific to PGT. From these data, we identified a PGT-enriched BAHD acyltransferase gene ObCAAT1 and functionally characterized it. In vitro coupled reaction of ObCAAT1 with eugenol synthase in the presence of coniferyl alcohol resulted in eugenol production. Analysis of ObCAAT1-RNAi transgenic lines showed decreased levels of eugenol and accumulation of coniferyl alcohol and its derivatives. Coniferyl alcohol acts as a common substrate for phenylpropene and lignin biosynthesis. No differences were found in total lignin content of PGTs and leaves of transgenic lines, indicating that phenylpropene biosynthesis is not coupled to lignification in sweet basil.

中文翻译：

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甜丁香酚生物合成中涉及的甜罗勒酰基转移酶的表征。

甜罗勒（罗勒罗勒）植物在称为状腺毛（PGTs）的特殊结构中生产其特征性的富含苯丙烯的精油。丁香酚和香豆酚是甜罗勒品种生产的主要苯基丙烯，其合成途径尚未完全阐明。丁香酚通过丁香酚合酶催化的反应衍生自乙酸松柏酯。提出了酰基转移酶将松柏基醇转化为乙酸松柏基酯，这是向丁子香酚合成的第一步。在这里，我们对甜罗勒的不同组织（即PGT，叶，PGT剥离的叶子（叶–PGT）和根）进行比较的下一代转录组测序，以鉴定特定于PGT的差异表达转录本。从这些数据，我们确定了富含PGT的BAHD酰基转移酶基因ObCAAT1并在功能上对其进行了表征。在松柏醇存在下，ObCAAT1与丁香酚合酶的体外偶联反应导致丁香酚的产生。分析ObCAAT1 -RNAi转基因品系显示降低丁子香酚和松柏醇及其衍生物的积累水平。松柏醇是苯丙烯和木质素生物合成的常用底物。在PGT和转基因品系的叶片中，木质素的总含量未发现差异，表明苯丙烯的生物合成与甜罗勒中的木质化不相关。