Santalum album L. is an economically important species that can produce highly valued essential oil (EO) consisting mainly of santalols in its aromatic heartwood. Elicitors stimulate the production of EO, but the underlying mechanism remains unknown. In this study, the regulatory role and ability of a cytokinin (6-benzyladenine, BA) to promote the accumulation of secondary metabolites, was investigated. The levels of EO and total flavonoids increased 2.3- and 1.5-fold, respectively one year after BA treatment. The top significantly enriched Kyoto Encyclopedia of Genes and Genomes pathways of upregulated differentially expressed genes (DEGs) and differentially accumulated metabolites contained ‘terpenoid biosynthesis’, ‘phenylpropanoid biosynthesis’, and ‘flavonoids biosynthesis’, displaying similar profiles to those detected in natural heartwood from 10-year-old trees. Prominently, the content of santalols was increased by approximately 90-fold by BA relative to the control and was associated with the contents of flavonoids and phenolics. BA also enhanced the contents of cytokinins, an auxin (IAA), gibberellins, jasmonic acid and an ethylene precursor while DEGs associated with the biosynthesis and signaling of these hormones were significantly upregulated. Dual-LUC assays confirmed that identified SaMYC2a-2c and three SaERFs activated SaSSY and SaCYP736A167 expression. Moreover, exogenous BA regulated EO biosynthesis in sandalwood suspension cells but could not directly activate the expression of these two genes in these cells. We infer from these findings that exogenously applied BA positively participated in the biosynthesis of sandalwood EO by interacting with other hormones. These findings also reveal details of the regulatory mechanism underlying the cytokinin-induced production of secondary metabolites, which determine the fragrance and color of S. album heartwood.

中文翻译：

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6-苄基腺嘌呤是一种细胞分裂素，通过与其他激素相互作用，促进檀香专辑心材中精油、类黄酮和酚类物质的积累


檀香专辑 L. 是一种经济上重要的物种，可以生产高价值的精油 （EO），其芳香心材中主要由檀香醇组成。诱发剂刺激 EO 的产生，但其潜在机制仍不清楚。在这项研究中，研究了细胞分裂素 （6-苄基腺嘌呤，BA） 促进次生代谢物积累的调节作用和能力。BA 处理后 1 年，EO 和总黄酮水平分别增加了 2.3 倍和 1.5 倍。上调差异表达基因 （DEG） 和差异积累代谢物的显着富集京都基因和基因组百科全书通路中，包含“类萜类生物合成”、“苯丙烷生物合成”和“类黄酮生物合成”，显示出与在 10 年树龄树的天然心材中检测到的相似特征。值得注意的是，BA 相对于对照增加了约 90 倍的檀香醇含量，并且与类黄酮和酚类化合物的含量有关。BA 还提高了细胞分裂素、生长素 （IAA）、赤霉素、茉莉酸和乙烯前体的含量，而与这些激素的生物合成和信号传导相关的 DEGs 显着上调。双 LUC 测定证实，鉴定出的 SaMYC2a-2c 和 3 个 SaERF 激活了 SaSSY 和 SaCYP736A167 的表达。此外，外源 BA 调节檀香木悬浮细胞中 EO 的生物合成，但不能直接激活这两个基因在这些细胞中的表达。从这些发现中，我们推断外源性应用 BA 通过与其他激素相互作用积极参与檀香木 EO 的生物合成。 这些发现还揭示了细胞分裂素诱导产生次生代谢物的调节机制的细节，这些代谢物决定了 S. album 心材的香味和颜色。