King Abdullah University of Science and Technology, Biological and Environmental Sciences and Engineering Division, The Bioactives Lab, Thuwal, Kingdom of Saudi Arabia.
J Exp Bot. 2018 Apr 23;69(9):2189-2204. doi: 10.1093/jxb/erx476.
Strigolactones are phytohormones that regulate various plant developmental and adaptation processes. When released into soil, strigolactones act as chemical signals, attracting symbiotic arbuscular mycorrhizal fungi and inducing seed germination in root-parasitic weeds. Strigolactones are carotenoid derivatives, characterized by the presence of a butenolide ring that is connected by an enol ether bridge to a less conserved second moiety. Carotenoids are isopenoid pigments that differ in structure, number of conjugated double bonds, and stereoconfiguration. Genetic analysis and enzymatic studies have demonstrated that strigolactones originate from all-trans-β-carotene in a pathway that involves the all-trans-/9-cis-β-carotene isomerase DWARF27 and carotenoid cleavage dioxygenase 7 and 8 (CCD7, 8). The CCD7-mediated, regiospecific and stereospecific double-bond cleavage of 9-cis-β-carotene leads to a 9-cis-configured intermediate that is converted by CCD8 via a combination of reactions into the central metabolite carlactone. By catalyzing repeated oxygenation reactions that can be coupled to ring closure, CYP711 enzymes convert carlactone into tricyclic-ring-containing canonical and non-canonical strigolactones. Modifying enzymes, which are mostly unknown, further increase the diversity of strigolactones. This review explores carotenogenesis, provides an update on strigolactone biosynthesis, with emphasis on the substrate specificity and reactions catalyzed by the different enzymes, and describes the regulation of the biosynthetic pathway.
独脚金内酯是一类植物激素，调控多种植物发育和适应过程。独脚金内酯释放到土壤中时，作为化学信号，吸引共生菌丛枝菌根真菌，并诱导根寄生杂草种子萌发。独脚金内酯是类胡萝卜素衍生物，特征是存在丁烯内酯环，通过烯醇醚桥与不太保守的第二部分连接。类胡萝卜素是异戊二烯色素，在结构、共轭双键数目和立体构型上存在差异。遗传分析和酶学研究表明，独脚金内酯来源于全反式-β-胡萝卜素，涉及全反式/9-顺式-β-胡萝卜素异构酶 DWARF27 和类胡萝卜素裂解双加氧酶 7 和 8（CCD7、8）。CCD7 介导的、区域和立体特异性的 9-顺式-β-胡萝卜素双键断裂导致生成 9-顺式构型的中间产物，该中间产物通过 CCD8 结合反应转化为中央代谢产物 carlactone。CYP711 酶通过重复的加氧反应催化，可与环化偶联，将 carlactone 转化为含有三环的典型和非典型独脚金内酯。大部分未知的修饰酶进一步增加了独脚金内酯的多样性。本文探讨了类胡萝卜素生物合成，概述了独脚金内酯生物合成，重点介绍了不同酶的底物特异性和催化反应，并描述了生物合成途径的调控。
