Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba, 260-8675, Japan.
RIKEN Center for Sustainable Resource Science, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, 230-0045, Japan.
Plant J. 2019 Nov;100(3):505-521. doi: 10.1111/tpj.14454. Epub 2019 Aug 27.
Lysine decarboxylase converts l-lysine to cadaverine as a branching point for the biosynthesis of plant Lys-derived alkaloids. Although cadaverine contributes towards the biosynthesis of Lys-derived alkaloids, its catabolism, including metabolic intermediates and the enzymes involved, is not known. Here, we generated transgenic Arabidopsis lines by expressing an exogenous lysine/ornithine decarboxylase gene from Lupinus angustifolius (La-L/ODC) and identified cadaverine-derived metabolites as the products of the emerged biosynthetic pathway. Through untargeted metabolic profiling, we observed the upregulation of polyamine metabolism, phenylpropanoid biosynthesis and the biosynthesis of several Lys-derived alkaloids in the transgenic lines. Moreover, we found several cadaverine-derived metabolites specifically detected in the transgenic lines compared with the non-transformed control. Among these, three specific metabolites were identified and confirmed as 5-aminopentanal, 5-aminopentanoate and δ-valerolactam. Cadaverine catabolism in a representative transgenic line (DC29) was traced by feeding stable isotope-labeled [α- N]- or [ε- N]-l-lysine. Our results show similar N incorporation ratios from both isotopomers for the specific metabolite features identified, indicating that these metabolites were synthesized via the symmetric structure of cadaverine. We propose biosynthetic pathways for the metabolites on the basis of metabolite chemistry and enzymes known or identified through catalyzing specific biochemical reactions in this study. Our study shows that this pool of enzymes with promiscuous activities is the driving force for metabolite diversification in plants. Thus, this study not only provides valuable information for understanding the catabolic mechanism of cadaverine but also demonstrates that cadaverine accumulation is one of the factors to expand plant chemodiversity, which may lead to the emergence of Lys-derived alkaloid biosynthesis.
赖氨酸脱羧酶将 L-赖氨酸转化为尸胺，作为植物赖氨酸衍生生物碱生物合成的分支点。虽然尸胺有助于赖氨酸衍生生物碱的生物合成，但它的分解代谢，包括代谢中间产物和涉及的酶，尚不清楚。在这里，我们通过表达来自 Lupinus angustifolius 的外源赖氨酸/鸟氨酸脱羧酶基因（La-L/ODC）生成了转基因拟南芥系，并鉴定出尸胺衍生代谢物作为新出现的生物合成途径的产物。通过非靶向代谢谱分析，我们观察到在转基因系中多胺代谢、苯丙烷生物合成和几种赖氨酸衍生生物碱的生物合成上调。此外，我们发现与非转化对照相比，在转基因系中特异性检测到几种尸胺衍生代谢物。其中，鉴定并确证了三种特定的代谢物为 5-氨基戊醛、5-氨基戊酸和 δ-缬草酸内酯。通过用稳定同位素标记的 [α- N]-或 [ε- N]-L-赖氨酸喂养代表性转基因系（DC29）来追踪尸胺的分解代谢。我们的结果表明，从两种同位素标记物中都得到了相似的 N 掺入比，用于鉴定的特定代谢物特征，这表明这些代谢物是通过尸胺的对称结构合成的。根据代谢物化学和通过本研究中催化特定生化反应鉴定或识别的酶，我们提出了代谢物的生物合成途径。我们的研究表明，这种具有混杂活性的酶库是植物代谢物多样化的驱动力。因此，本研究不仅为理解尸胺的分解代谢机制提供了有价值的信息，还表明尸胺积累是扩大植物化学多样性的因素之一，这可能导致赖氨酸衍生生物碱生物合成的出现。
