Ghent University, Department of Plant Biotechnology and Bioinformatics, 9052 Ghent, Belgium.
VIB Center for Plant Systems Biology, 9052 Ghent, Belgium.
Plant Cell. 2020 Jun;32(6):2020-2042. doi: 10.1105/tpc.19.00609. Epub 2020 Apr 17.
Plants produce a vast array of defense compounds to protect themselves from pathogen attack or herbivore predation. Saponins are a specific class of defense compounds comprising bioactive glycosides with a steroidal or triterpenoid aglycone backbone. The model legume synthesizes two types of saponins, hemolytic saponins and nonhemolytic soyasaponins, which accumulate as specific blends in different plant organs. Here, we report the identification of the seed-specific transcription factor TRITERPENE SAPONIN ACTIVATION REGULATOR3 (TSAR3), which controls hemolytic saponin biosynthesis in developing seeds. Analysis of genes that are coexpressed with in transcriptome data sets from developing seeds led to the identification of CYP88A13, a cytochrome P450 that catalyzes the C-16α hydroxylation of medicagenic acid toward zanhic acid, the final oxidation step of the hemolytic saponin biosynthesis branch in In addition, two uridine diphosphate glycosyltransferases, UGT73F18 and UGT73F19, which glucosylate hemolytic sapogenins at the C-3 position, were identified. The genes encoding the identified biosynthetic enzymes are present in clusters of duplicated genes in the genome. This appears to be a common theme among saponin biosynthesis genes, especially glycosyltransferases, and may be the driving force of the metabolic evolution of saponins.
植物产生大量防御化合物来保护自己免受病原体攻击或草食动物捕食。皂苷是一类具有生物活性的糖苷的特定防御化合物，其糖苷配基具有甾体或三萜骨架。模式豆科植物合成两种类型的皂苷，溶血皂苷和非溶血大豆皂苷，它们作为特定的混合物在不同的植物器官中积累。在这里，我们报告了种子特异性转录因子三萜皂苷激活调节剂 3（TSAR3）的鉴定，它控制着发育中的种子中的溶血皂苷生物合成。对与 在来自发育中的种子的转录组数据集中共表达的基因进行分析，导致鉴定出 CYP88A13，这是一种细胞色素 P450，它催化 medicagenic 酸向 zanhic 酸的 C-16α羟化，这是溶血皂苷生物合成分支的最后氧化步骤在 中。此外，还鉴定了两种尿苷二磷酸糖基转移酶 UGT73F18 和 UGT73F19，它们将溶血皂素苷元在 C-3 位葡糖基化。编码鉴定出的生物合成酶的基因存在于 基因组中的基因簇中。这似乎是皂苷生物合成基因的一个共同主题，特别是糖基转移酶，并且可能是皂苷代谢进化的驱动力。
