Department of Plant Biology, University of California, Davis, California.
Section of Cell and Developmental Biology, University of California, La Jolla, California.
Plant Physiol. 2018 Apr;176(4):2677-2690. doi: 10.1104/pp.17.01351. Epub 2018 Feb 23.
Terpenoids are a major component of maize () chemical defenses that mediate responses to herbivores, pathogens, and other environmental challenges. Here, we describe the biosynthesis and elicited production of a class of maize diterpenoids, named dolabralexins. Dolabralexin biosynthesis involves the sequential activity of two diterpene synthases, -COPALYL DIPHOSPHATE SYNTHASE (ZmAN2) and KAURENE SYNTHASE-LIKE4 (ZmKSL4). Together, ZmAN2 and ZmKSL4 form the diterpene hydrocarbon dolabradiene. In addition, we biochemically characterized a cytochrome P450 monooxygenase, ZmCYP71Z16, which catalyzes the oxygenation of dolabradiene to yield the epoxides 15,16-epoxydolabrene (epoxydolabrene) and 3β-hydroxy-15,16-epoxydolabrene (epoxydolabranol). The absence of dolabradiene and epoxydolabranol in mutants under elicited conditions confirmed the in vivo biosynthetic requirement of ZmAN2. Combined mass spectrometry and NMR experiments demonstrated that much of the epoxydolabranol is further converted into 3β,15,16-trihydroxydolabrene (trihydroxydolabrene). Metabolite profiling of field-grown maize root tissues indicated that dolabralexin biosynthesis is widespread across common maize cultivars, with trihydroxydolabrene as the predominant diterpenoid. Oxidative stress induced dolabralexin accumulation and transcript expression of and in root tissues, and metabolite and transcript accumulation were up-regulated in response to elicitation with the fungal pathogens and Consistently, epoxydolabranol significantly inhibited the growth of both pathogens in vitro at 10 µg mL, while trihydroxydolabrene-mediated inhibition was specific to These findings suggest that dolabralexins have defense-related roles in maize stress interactions and expand the known chemical space of diterpenoid defenses as genetic targets for understanding and ultimately improving maize resilience.
萜类化合物是玉米化学防御的主要成分，可介导对草食动物、病原体和其他环境挑战的反应。在这里，我们描述了一类名为 dolabralexin 的玉米二萜的生物合成和诱导产生。Dolabralexin 的生物合成涉及两种二萜合酶的顺序活性，即 -COPALYL DIPHOSPHATE SYNTHASE（ZmAN2）和 KAURENE SYNTHASE-LIKE4（ZmKSL4）。ZmAN2 和 ZmKSL4 共同形成二萜烃 dolabradiene。此外，我们还对细胞色素 P450 单加氧酶 ZmCYP71Z16 进行了生物化学表征，该酶催化 dolabradiene 的氧化生成环氧化物 15,16-epoxydolabrene（环氧 dolabrene）和 3β-羟基-15,16-epoxydolabrene（环氧 dolabranol）。在诱导条件下， 突变体中缺乏 dolabradiene 和环氧 dolabranol 证实了 ZmAN2 的体内生物合成需求。结合质谱和 NMR 实验表明，大部分环氧 dolabranol 进一步转化为 3β,15,16-三羟基 dolabrene（三羟基 dolabrene）。田间生长的玉米根组织代谢产物分析表明， dolabralexin 生物合成在常见玉米品种中广泛存在，三羟基 dolabrene 是主要的二萜。氧化应激诱导 dolabralexin 积累和 及 在根组织中的转录表达，并且代谢物和转录物的积累对真菌病原体 和 的诱导表现出上调。一致地，环氧 dolabranol 在 10 µg mL 时显著抑制了两种病原体的体外生长，而三羟基 dolabrene 介导的抑制作用仅针对 这些发现表明， dolabralexin 在玉米应激相互作用中具有防御相关作用，并扩展了已知的二萜防御化学空间，作为理解和最终提高玉米弹性的遗传靶标。
