Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, the Chinese Academy of Sciences, Guangzhou 510650, China; University of Chinese Academy of Sciences, Beijing 100039, China.
Guangxi Academy of Agricultural Sciences, Nanning 530007, China.
Gene. 2023 Jan 30;851:146762. doi: 10.1016/j.gene.2022.146762. Epub 2022 Aug 3.
The commercial value of Santalum album L. lies in its aromatic heartwood and essential oil. Sesquiterpenes are the main components of sandal essential oil, and these are synthesized through the plant's mevalonate (MVA) and methylerythritol phosphate (MEP) pathways. In this study, the first key rate-limiting enzyme, 1-deoxy-d-xylulose-5-phosphate synthase (SaDXS), was investigated to provide a theoretical molecular basis for the sandalwood MEP sesquiterpene biosynthetic pathway. The biofunctions of SaDXS were also analyzed. SaDXS promoters were successfully cloned from a seven-year-old S. album tree. SaDXS1A/1B promoter activity was verified by a β-glucuronidase (GUS) assay and by analyzing cis-acting elements of the promoters, which carried light- and methyl jasmonate (MeJA)-responsive signals. In an experiment involving yellow S. album seedlings, exposure to light upregulated SaDXS1A/1B expression and increased chlorophyll and carotenoid contents when overexpressed in Arabidopsis thaliana. Analysis of the expression of SaDXS1A/1B and SaSSy, key genes of santalol biosynthesis, revealed SaDXS1A expression in all tissues whereas SaDXS1B was expressed in tissues that contained photosynthetic pigments, such as stems, leaves and flowers. Sandal seedlings exogenously treated with two hormones, MeJA and ethylene, revealed similar expression patterns for SaDXS1A/1B and SaSSy. Sandal seedlings were treated with an inhibitor of DXS, clomazone, but showed no significant changes in the contents of α-santalene, β-santalene and α-santalol between treatment and control groups. These results suggest that SaDXS1A/1B play a role in the synthesis of sandalwood sesquiterpenes, providing carbon for downstream secondary metabolites. SaDXS1A/1B also play a role in the biosynthesis of chlorophyll, carotenoids, and primary metabolites.
檀香的商业价值在于其芳香的心材和精油。倍半萜烯是檀香精油的主要成分，这些成分是通过植物的甲羟戊酸（MVA）和甲基赤藓醇磷酸（MEP）途径合成的。在这项研究中，第一个关键限速酶 1-脱氧-D-木酮糖-5-磷酸合酶（SaDXS）被研究，为檀香 MEP 倍半萜生物合成途径提供了理论分子基础。还分析了 SaDXS 的生物功能。从一棵七年生的檀香树上成功克隆了 SaDXS 启动子。通过 β-葡萄糖醛酸酶（GUS）测定和分析启动子的顺式作用元件，证实了 SaDXS1A/1B 启动子的活性，该元件携带光和茉莉酸甲酯（MeJA）响应信号。在涉及黄色檀香幼苗的实验中，光照上调了 SaDXS1A/1B 的表达，在拟南芥中过表达时增加了叶绿素和类胡萝卜素的含量。分析 SaDXS1A/1B 和 santalol 生物合成关键基因 SaSSy 的表达表明，SaDXS1A 在所有组织中表达，而 SaDXS1B 仅在含有光合色素的组织中表达，如茎、叶和花。用两种激素茉莉酸甲酯和乙烯处理檀香幼苗，SaDXS1A/1B 和 SaSSy 的表达模式相似。用 DXS 抑制剂氯甲唑啉处理檀香幼苗，但处理组和对照组之间 α-檀香烯、β-檀香烯和 α-檀香醇的含量没有显著变化。这些结果表明，SaDXS1A/1B 参与檀香倍半萜的合成，为下游次生代谢物提供碳。SaDXS1A/1B 还参与叶绿素、类胡萝卜素和初级代谢物的生物合成。
