Wakabayashi Takatoshi, Ueno Kotomi, Sugimoto Yukihiro
Graduate School of Agricultural Science, Kobe University, Kobe, Japan.
Faculty of Agriculture, Tottori University, Tottori, Japan.
Front Plant Sci. 2022 Feb 9;13:835160. doi: 10.3389/fpls.2022.835160. eCollection 2022.
Strigolactones (SLs), a class of phytohormones that regulate diverse developmental processes, were initially characterized as host-derived germination stimulants for seeds belonging to the genera , , and . Orobanchol (), which is detected in the root exudates of several plants and recognized as a prevalent SL, was first isolated from the root exudates of red clover as a germination stimulant for in 1998. However, the structure of this stimulant proposed at that time was disputable considering its predicted germination-inducing activity for . The genuine structure of orobanchol was elucidated following a decade-long controversy, which ultimately facilitated the understanding of the importance of SL stereochemistry in seed germination. Recently, studies focusing on clarifying the biosynthesis pathway of orobanchol are being conducted. Cytochrome P450 monooxygenases are involved in orobanchol biosynthesis downstream of carlactonoic acid (CLA) via two pathways: either through 4-deoxyorobanchol or direct conversion from CLA. Substantial progress in the identification of more SL structures and clarification of their biosynthetic mechanisms will further contribute in the comprehension of their structural diversity's functional importance and agricultural applications. Herein, we have reviewed the history leading to the discovery of the genuine structure of orobanchol and the current understanding of its biosynthetic mechanisms.
独脚金内酯（SLs）是一类调节多种发育过程的植物激素，最初被表征为列当属、独脚金属和百蕊草属种子的宿主衍生萌发刺激物。1998年，从红三叶草的根分泌物中首次分离出一种在几种植物的根分泌物中都能检测到且被认为是一种普遍存在的独脚金内酯——列当醇（orobanchol），它作为一种萌发刺激物可刺激埃及列当种子萌发。然而，考虑到其对列当属种子预测的萌发诱导活性，当时提出的这种刺激物的结构存在争议。经过长达十年的争论，列当醇的真实结构得以阐明，这最终促进了对独脚金内酯立体化学在列当属种子萌发中重要性的理解。最近，人们正在开展专注于阐明列当醇生物合成途径的研究。细胞色素P450单加氧酶通过两条途径参与列当醇在独脚金烯酸（CLA）下游的生物合成：要么通过4-脱氧列当醇，要么直接从CLA转化。在鉴定更多独脚金内酯结构及其生物合成机制的阐明方面取得的实质性进展，将进一步有助于理解其结构多样性的功能重要性和农业应用。在此，我们回顾了导致列当醇真实结构发现的历程以及目前对其生物合成机制的理解。
