1] Department of Plant Systems Biology, VIB, Technologiepark 927, Gent B-9052, Belgium [2] Department of Plant Biotechnology and Bioinformatics, Ghent University, Technologiepark 927, Gent B-9052, Belgium [3].
Nature. 2013 Dec 5;504(7478):148-52. doi: 10.1038/nature12685. Epub 2013 Nov 10.
Jasmonates are ubiquitous oxylipin-derived phytohormones that are essential in the regulation of many development, growth and defence processes. Across the plant kingdom, jasmonates act as elicitors of the production of bioactive secondary metabolites that serve in defence against attackers. Knowledge of the conserved jasmonate perception and early signalling machineries is increasing, but the downstream mechanisms that regulate defence metabolism remain largely unknown. Here we show that, in the legume Medicago truncatula, jasmonate recruits the endoplasmic-reticulum-associated degradation (ERAD) quality control system to manage the production of triterpene saponins, widespread bioactive compounds that share a biogenic origin with sterols. An ERAD-type RING membrane-anchor E3 ubiquitin ligase is co-expressed with saponin synthesis enzymes to control the activity of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR), the rate-limiting enzyme in the supply of the ubiquitous terpene precursor isopentenyl diphosphate. Thus, unrestrained bioactive saponin accumulation is prevented and plant development and integrity secured. This control apparatus is equivalent to the ERAD system that regulates sterol synthesis in yeasts and mammals but that uses distinct E3 ubiquitin ligases, of the HMGR degradation 1 (HRD1) type, to direct destruction of HMGR. Hence, the general principles for the management of sterol and triterpene saponin biosynthesis are conserved across eukaryotes but can be controlled by divergent regulatory cues.
茉莉酸是普遍存在的氧化脂类植物激素，在许多发育、生长和防御过程的调节中是必不可少的。在整个植物界，茉莉酸作为生物活性次生代谢物产生的激发子，在抵御攻击者方面发挥作用。对保守的茉莉酸感知和早期信号机制的了解正在增加，但调节防御代谢的下游机制在很大程度上仍然未知。在这里，我们表明，在豆科植物苜蓿中，茉莉酸招募内质网相关降解（ERAD）质量控制系统来管理三萜皂苷的产生，三萜皂苷是广泛存在的生物活性化合物，与固醇具有共同的生物起源。一种 ERAD 型 RING 膜锚定 E3 泛素连接酶与皂苷合成酶共同表达，以控制 3-羟-3-甲基戊二酰辅酶 A 还原酶（HMGR）的活性，HMGR 是提供普遍存在的萜烯前体异戊烯二磷酸的限速酶。因此，不受控制的生物活性皂苷积累被阻止，植物的发育和完整性得到保障。这个控制装置相当于调节酵母和哺乳动物固醇合成的 ERAD 系统，但使用不同的 E3 泛素连接酶，即 HRD1 型，来指导 HMGR 的破坏。因此，固醇和三萜皂苷生物合成的管理的一般原则在真核生物中是保守的，但可以通过不同的调节信号来控制。
