Huang Xing-Qi, Yahyaa Mosaab, Kongala Prasada Rao, Maoz Itay, Dudareva Natalia, Ibdah Mwafaq
Department of Biochemistry, Purdue University, 175 S. University Street, West Lafayette, Indiana, 47907-2063, USA.
Purdue Center for Plant Biology, Purdue University, West Lafayette, Indiana, 47907, USA.
Plant J. 2025 Jan;121(2):e17201. doi: 10.1111/tpj.17201. Epub 2024 Dec 18.
Volatile phenylpropenes comprise one of the largest groups of plant phenylalanine-derived volatiles that not only possess ecological roles but also exhibit numerous pharmacological activities. Despite their wide distribution in the plant kingdom, biosynthesis of only a small subset of these compounds has been discovered. Here, we elucidated yet unknown steps in the biosynthesis of isoelemicin and elemicin using carrot (Daucus carota subsp. sativus), which produces a wide spectrum of volatile phenylpropenes, as a model system. Comparative transcriptomic analysis combined with metabolic profiling of two carrot cultivars producing different spectrums and levels of phenylpropene compounds revealed that biosynthesis of isoelemicin and elemicin could proceed via the (iso)eugenol-independent pathway, which diverges from the lignin biosynthetic pathway after sinapyl alcohol. Moreover, in planta results showed that two different NADPH-dependent reductases, a newly identified 5-methoxy isoeugenol synthase (DcMIS) and previously characterized (iso)eugenol synthase (DcE(I)GS1), both of which use sinapyl acetate as a substrate, are responsible for the biosynthesis of immediate precursors of isoelemicin and elemicin, respectively. In contrast to penultimate reactions, the final steps in the formation of these phenylpropenes are catalyzed by the same newly characterized methyltransferase, S-adenosyl-l-methionine:5-methoxy(iso)eugenol O-methyltransferase, that methylates the para-hydroxyl group of their respective precursors, thus completing the (iso)eugenol-independent route for the biosynthesis of isoelemicin and elemicin.
挥发性苯丙烯类化合物是植物苯丙氨酸衍生挥发物中最大的类别之一，它们不仅具有生态作用，还展现出众多药理活性。尽管这些化合物在植物界广泛分布，但目前仅发现了其中一小部分的生物合成途径。在此，我们以胡萝卜（Daucus carota subsp. sativus）为模型系统，阐明了异榄香脂素和榄香脂素生物合成中尚未知晓的步骤，胡萝卜能产生多种挥发性苯丙烯类化合物。对两个产生不同种类和水平苯丙烯类化合物的胡萝卜品种进行比较转录组分析，并结合代谢谱分析，结果表明异榄香脂素和榄香脂素的生物合成可能通过不依赖（异）丁香酚的途径进行，该途径在芥子醇之后与木质素生物合成途径分道扬镳。此外，在植物体内的研究结果显示，两种不同的依赖NADPH的还原酶，即新鉴定的5-甲氧基异丁香酚合酶（DcMIS）和先前已表征的（异）丁香酚合酶（DcE(I)GS1），均以乙酸芥子酯为底物，分别负责异榄香脂素和榄香脂素直接前体的生物合成。与倒数第二步反应不同，这些苯丙烯类化合物形成的最后步骤由同一种新表征的甲基转移酶——S-腺苷-L-甲硫氨酸：5-甲氧基（异）丁香酚O-甲基转移酶催化，该酶将各自前体的对羟基甲基化，从而完成了异榄香脂素和榄香脂素不依赖（异）丁香酚的生物合成途径。
