Main conclusion 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 Abstract 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 ( SC s), 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.

中文翻译：

---

蕨类植物三萜化学表型的分子基础

主要结论 提出了一个假设，即角鲨烯环化酶基因广泛分布于整个蕨类植物中。我们成功地从没有检测到三萜烃的蕨类植物中分离出角鲨烯环化酶假基因。 摘要蕨类植物是最原始的维管植物，分布于热带至寒温带、低地至高寒地带。三萜烃及其衍生物是蕨类植物的特征性代谢物，也是化学表观标志物。最近，我们对蕨类角鲨烯环化酶 (SC s)（负责三萜合成的酶）的生物合成研究得出了基因型（酶功能）和化学型（三萜谱）之间出乎意料的不一致。这一发现促使我们提出一个假设，即 SC 基因广泛分布于蕨类植物和石松植物中，无论它们是否产生三萜烃。为了验证这一假设，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，我们成功地从没有或仅检测到一种三萜烃的蕨类植物中分离出两个 SC 假基因。随后的诱变实验导致这些假基因功能性转化为活性 SC 基因。鉴于简并聚合酶链反应 (PCR) 方法的固有限制的辅助假设，整个数据集支持我们的假设，尽管需要对植物覆盖率进行校正。