Showa Pharmaceutical University, 3-3165 Higashi-Tamagawagakuen, Machida, Tokyo, 194-8543, Japan.
Planta. 2020 Mar 10;251(4):78. doi: 10.1007/s00425-020-03369-3.
A hypothesis that squalene cyclase genes are widely distributed throughout ferns was proposed. We successfully isolated a squalene cyclase pseudogene from a fern from which no triterpene hydrocarbons were detected Ferns are the most primitive vascular plants, with their locations ranging from tropical to cold temperate regions and from lowland to alpine zones. The triterpene hydrocarbons and their derivatives are characteristic fern metabolites, and are also chemophenetic markers. Recently, our biosynthetic study into fern squalene cyclases (SCs), the enzymes responsible for triterpene synthesis, gave an unexpected inconsistency between genotype (enzyme function) and chemotype (triterpene profile). This finding prompted us to propose a hypothesis that SC genes are widely distributed throughout ferns and lycophytes whether or not they produce triterpene hydrocarbons. To test this hypothesis, we employed a multifaceted approach based on phytochemical, biochemical, and phylogenetic analyses. As anticipated, we successfully isolated two SC pseudogenes from a fern from in which no or only one triterpene hydrocarbon was detected. Subsequent mutagenesis experiments resulted in the functional conversion of these pseudogenes into active SC genes. Given an auxiliary hypothesis regarding the inherent limit of the degenerate polymerase chain reaction (PCR) method, the overall dataset supported our hypothesis, although correction was required with respect to plant coverage. Not only did the corrected hypothesis outline the distribution of SC genes throughout ferns, it provided insight into the molecular basis of the triterpene-based chemophenetics in ferns, which is also discussed.
提出了一个假说，即角鲨烯环化酶基因广泛分布于蕨类植物中。我们成功地从一种未检测到三萜类碳氢化合物的蕨类植物中分离出一个角鲨烯环化酶假基因。蕨类植物是最原始的维管植物，分布范围从热带到寒温带，从低地到高山地带。三萜类碳氢化合物及其衍生物是蕨类植物特有的代谢产物，也是化学分类学的标志物。最近，我们对角鲨烯环化酶（SCs）的生物合成研究，这种酶负责三萜类合成，发现基因型（酶功能）和化学型（三萜类谱）之间存在出乎意料的不一致。这一发现促使我们提出一个假说，即 SC 基因广泛分布于蕨类植物和石松类植物中，无论它们是否产生三萜类碳氢化合物。为了验证这一假说，我们采用了基于植物化学、生化和系统发育分析的多方面方法。正如预期的那样，我们成功地从一种未检测到三萜类碳氢化合物或只检测到一种三萜类碳氢化合物的蕨类植物中分离出两个 SC 假基因。随后的突变实验导致这些假基因转化为具有活性的 SC 基因。根据关于退化聚合酶链反应（PCR）方法固有局限性的辅助假设，总体数据集支持我们的假说，尽管需要对植物覆盖范围进行修正。修正后的假说不仅概述了 SC 基因在蕨类植物中的分布，还提供了对蕨类植物基于三萜类化学分类学的分子基础的深入了解，这也在讨论中进行了探讨。
