Plants synthesize many diverse small molecules that affect function of the mammalian central nervous system, making them crucial sources of therapeutics for neurological disorders. A notable portion of neuroactive phytochemicals are lysine-derived alkaloids, but the mechanisms by which plants produce these compounds have remained largely unexplored. To better understand how plants synthesize these metabolites, we focused on biosynthesis of the Lycopodium alkaloids that are produced by club mosses, a clade of plants used traditionally as herbal medicines. Hundreds of Lycopodium alkaloids have been described, including huperzine A (HupA), an acetylcholine esterase inhibitor that has generated interest as a treatment for the symptoms of Alzheimer’s disease. Through combined metabolomic profiling and transcriptomics, we have identified a developmentally controlled set of biosynthetic genes, or potential regulon, for the Lycopodium alkaloids. The discovery of this putative regulon facilitated the biosynthetic reconstitution and functional characterization of six enzymes that act in the initiation and conclusion of HupA biosynthesis. This includes a type III polyketide synthase that catalyzes a crucial imine-polyketide condensation, as well as three Fe(II)/2-oxoglutarate–dependent dioxygenase (2OGD) enzymes that catalyze transformations (pyridone ring-forming desaturation, piperidine ring cleavage, and redox-neutral isomerization) within downstream HupA biosynthesis. Our results expand the diversity of known chemical transformations catalyzed by 2OGDs and provide mechanistic insight into the function of noncanonical type III PKS enzymes that generate plant alkaloid scaffolds. These data offer insight into the chemical logic of Lys-derived alkaloid biosynthesis and demonstrate the tightly coordinated coexpression of secondary metabolic genes for the biosynthesis of medicinal alkaloids.

植物合成许多影响哺乳动物中枢神经系统功能的不同小分子，使它们成为治疗神经系统疾病的重要来源。神经活性植物化学物质的一个显着部分是赖氨酸衍生的生物碱，但植物产生这些化合物的机制在很大程度上仍未得到探索。为了更好地了解植物如何合成这些代谢物，我们重点研究了由苔藓（传统上用作草药的植物进化枝）产生的石松生物碱的生物合成。已经描述了数百种石松生物碱，包括石杉碱甲 (HupA)，一种乙酰胆碱酯酶抑制剂，已引起人们对治疗阿尔茨海默病症状的兴趣。通过结合代谢组学分析和转录组学，我们已经为石松属生物碱鉴定了一组发育控制的生物合成基因，或潜在的调节子。这种假定的调节子的发现促进了在 HupA 生物合成的起始和结束中起作用的六种酶的生物合成重建和功能表征。这包括催化亚胺-聚酮化合物缩合的 III 型聚酮化合物合酶，以及催化转化（吡啶酮环形成去饱和、哌啶环裂解和氧化还原中性异构化）在下游 HupA 生物合成中。我们的研究结果扩展了由 2OGD 催化的已知化学转化的多样性，并提供了对生成植物生物碱支架的非经典 III 型 PKS 酶功能的机制洞察。这些数据提供了对赖氨酸衍生生物碱生物合成化学逻辑的深入了解，并证明了用于药用生物碱生物合成的次级代谢基因的紧密协调共表达。