Awasthi Praveen, Gupta Ajai Prakash, Bedi Yashbir S, Vishwakarma Ram A, Gandhi Sumit G
Indian Institute of Integrative Medicine (CSIR-IIIM), Council of Scientific and Industrial Research Jammu, India.
Quality Control, Quality Assurance & CMC Division, Council of Scientific and Industrial Research-Indian Institute of Integrative Medicine Jammu, India.
Front Plant Sci. 2016 Jul 6;7:985. doi: 10.3389/fpls.2016.00985. eCollection 2016.
Cytochrome P450 monooxygenases (CYP450s) are known to play important roles in biosynthesis of all secondary metabolites, including flavonoids. Despite this, few CYP450s have been functionally characterized in model plants and roles of fewer CYP450s are known in non-model, medicinal, and aromatic plants. Our study in Coleus forskohlii indicates that flavone synthase (CYP93B) and flavonoid 3' monooxygenase (CYP706C) are key enzymes positioned at a metabolic junction, to execute the biosynthesis of different sub-classes of flavonoids (flavones, flavonol, anthocynanin, isoflavones etc.) from a common precursor. Such branch points are favored targets for artificially modulating the metabolic flux toward specific metabolites, through genetic manipulation or use of elicitors that differentially impact the expression of branch point genes. Genkwanin, the only flavone reported from C. forskohlii, is known to possess anti-inflammatory activity. It is biosynthesized from the general flavonoid precursor: naringenin. Two differentially expressed cytochrome P450 genes (CfCYP93B, CfCYP706C), exhibiting maximum expression in leaf tissues, were isolated from C. forskohlii. Mannitol treatment resulted in increased expression of CfCYP93B and decrease in expression of CfCYP706C. Metabolite quantification data showed that genkwanin content increased and anthocyanin levels decreased in response to mannitol treatment. Alignment, phylogenetic analysis, modeling, and molecular docking analysis of protein sequences suggested that CfCYP93B may be involved in conversion of naringenin to flavones (possibly genkwanin via apigenin), while CfCYP706C may act on common precursors of flavonoid metabolism and channel the substrate toward production of flavonols or anthocynanins. Decrease in expression of CfCYP706C and increase in accumulation of genkwanin suggested that mannitol treatment may possibly lead to accumulation of genkwanin via suppression of a competitive branch of flavonoids in C. forskohlii.
细胞色素P450单加氧酶（CYP450s）在包括黄酮类化合物在内的所有次生代谢产物的生物合成中发挥着重要作用。尽管如此，在模式植物中，很少有CYP450s的功能得到表征，而在非模式植物、药用植物和芳香植物中，了解其功能的CYP450s更少。我们对毛喉鞘蕊花的研究表明，黄酮合酶（CYP93B）和类黄酮3'单加氧酶（CYP706C）是位于代谢节点的关键酶，可从共同前体执行不同亚类黄酮（黄酮、黄酮醇、花青素、异黄酮等）的生物合成。通过基因操作或使用对节点基因表达有不同影响的诱导剂，这些分支点有利于人工调节代谢通量以产生特定代谢产物。根皮苷是从毛喉鞘蕊花中报道的唯一黄酮，已知具有抗炎活性。它由一般的类黄酮前体：柚皮素生物合成。从毛喉鞘蕊花中分离出两个差异表达的细胞色素P450基因（CfCYP93B、CfCYP706C），它们在叶片组织中表达量最高。甘露醇处理导致CfCYP93B表达增加，CfCYP706C表达降低。代谢物定量数据表明，响应甘露醇处理，根皮苷含量增加，花青素水平降低。蛋白质序列的比对、系统发育分析、建模和分子对接分析表明，CfCYP93B可能参与柚皮素向黄酮的转化（可能通过芹菜素生成根皮苷），而CfCYP706C可能作用于类黄酮代谢的共同前体，并将底物导向黄酮醇或花青素的生成。CfCYP706C表达的降低和根皮苷积累的增加表明，甘露醇处理可能通过抑制毛喉鞘蕊花中黄酮类化合物的竞争分支而导致根皮苷的积累。
