Functional characterization of NADPH-cytochrome P450 reductase and cinnamic acid 4-hydroxylase encoding genes from Scoparia dulcis L

Functional characterization of two distinct classes of NADPH-cytochrome P450 reductases in Senna alexandrina Mill

BACKGROUND

Senna alexandrina Mill., an important medicinal plant of Fabaceae family, is famous for its laxative properties which are mainly due to the presence of sennosides (anthraquinone glycosides). However, the complete biosynthetic pathway of sennosides in Senna is not yet fully understood. Cytochrome P450 monooxygenases (CYPs), which are heme-containing enzymes are supposed to play key roles in sennoside biosynthesis. Cytochrome P450 reductases (CPRs) are essential for the activity of CYPs, as they function as their redox partners. However, CPRs in Senna have not yet been characterized in detail.

METHODS AND RESULTS

In this study, two different sequences of SaCPRs were retrieved from the publicly available Transcriptome Shotgun Assembly (TSA) database of S. alexandrina at National Center for Biotechnology Information (NCBI). The open reading frames of SaCPR1 and SaCPR2 were found to be 2079 and 2121 bp, encoding 693 and 707 amino acid long polypeptides, respectively. Phylogenetic and 3-D structure analysis predicted that these two SaCPRs (i.e. SaCPR1 and SaCPR2) were grouped with the members of Class I and Class II CPRs, respectively. Analysis of SaCPR1 and SaCPR2 sequences showed that the conserved domains commonly found in CPRs such as FMN- (Flavin adenine mononucleotide), FAD-(Flavin adenine dinucleotide), NADPH-(Nicotinamide adenine dinucleotide phosphate hydrogen) and cytochrome P450 binding region, were also present in SaCPRs. SaCPR1 and SaCPR2 were cloned and expressed in yeast for functional characterization. In cytochrome P450 reductase assay, both SaCPR1 and SaCPR2 reduced cytochrome c in the presence of NADPH as an electron donor, however, SaCPR1 showed higher specific activity than SaCPR2. The real time expression analysis of SaCPRs performed in the leaf, stem and root tissues of Senna showed that SaCPR1 was expressed more in leaf tissue while SaCPR2 expressed more in stem tissue. Furthermore, both the SaCPRs were found to be induced by salicylic acid as well as wound treatment (up to two hr).

CONCLUSION

Two different classes of cytochrome P450 reductases were identified and functionally characterized. SaCPR1 showed higher in vitro activity than SaCPR2 in cytochrome c reduction assay.

Biosynthesis of Soyasapogenol B by Engineered Saccharomyces cerevisiae

Soyasapogenol B is an oleanane-type pentacyclic triterpene that has various applications in food and healthcare and has a higher biological activity than soyasaponin. Saccharomyces cerevisiae is a potential platform for terpenoid production with mature genetic tools for metabolic pathway manipulation. In this study, we developed a biosynthesis method to produce soyasapogenol B. First, we expressed β-amyrin synthase derived from Glycyrrhiza glabra in S. cerevisiae to generate β-amyrin, as the precursor of soyasapogenol B. Several different types of promoters were then used to regulate the expression of key genes in the mevalonate pathway (MVA), and this subsequently increased the yield of β-amyrin to 17.6 mg/L, 25-fold more than that produced in the original strain L01 (0.68 mg/L). Then, using the β-amyrin-producing strain, we expressed soyasapogenol B synthases from Medicago truncatula (CYP93E2 and CYP72A61V2) and from G. glabra (CYP93E3 and CYP72A566). Soyasapogenol B yields were then optimized by using soyasapogenol B synthases and cytochrome P450 reductase from G. glabra. The most effective soyasapogenol B production strain was used for fermentation, and the yield of soyasapogenol B reached 2.9 mg/L in flask and 8.36 mg/L in a 5-L bioreactor with fed glucose and ethanol. This study demonstrated the heterologous synthesis of soyasapogenol B in S. cerevisiae using the combined expression of CYP93E3 and CYP72A566 in the synthesis pathway, which significantly increased the production of soyasapogenol B and provides a reference method for the biosynthesis of other triterpenes.

A Proteomics Study on the Mechanism of Nutmeg-Induced Hepatotoxicity

Nutmeg is a traditional spice and medicinal plant with a variety of pharmacological activities. However, nutmeg abuse due to its hallucinogenic characteristics and poisoning cases are frequently reported. Our previous metabolomics study proved the hepatotoxicity of nutmeg and demonstrated that high-dose nutmeg can affect the synthesis and secretion of bile acids and cause oxidative stress. In order to further investigate the hepatotoxicity of nutmeg, normal saline, 1 g/kg, 4 g/kg nutmeg were administrated to male Kunming mice by intragastrical gavage for 7 days. Histopathological investigation of liver tissue, proteomics and biochemical analysis were employed to explore the mechanism of liver damage caused by nutmeg. The results showed that a high-dose (4 g/kg) of nutmeg can cause significant increased level of CYP450s and depletion of antioxidants, resulting in obvious oxidative stress damage and lipid metabolism disorders; but this change was not observed in low-dose group (1 g/kg). In addition, the increased level of malondialdehyde and decreased level of glutathione peroxidase were found after nutmeg exposure. Therefore, the present study reasonably speculates that nutmeg exposure may lead to liver injury through oxidative stress and the degree of this damage is related to the exposure dose.

A Rehmannia glutinosa cinnamate 4-hydroxylase promotes phenolic accumulation and enhances tolerance to oxidative stress

RgC4H promotes phenolic accumulation in R. glutinosa, activating the molecular networks of its antioxidant systems, and enhancing the tolerance to oxidative stresses exposed to drought, salinity and H₂O₂ conditions. Rehmannia glutinosa is of great economic importance in China and increasing R. glutinosa productivity relies, in part, on understanding its tolerance to oxidative stress. Oxidative stress is a key influencing factor for crop productivity in plants exposed to harsh conditions. In the defense mechanisms of plants against stress, phenolics serve an important antioxidant function. Cinnamate 4-hydroxylase (C4H) is the first hydroxylase in the plant phenolics biosynthesis pathway, and elucidating the molecular characteristics of this gene in R. glutinosa is essential for understanding the effect of tolerance to oxidative stress tolerance on improving yield. Using in vitro and in silico methods, a C4H gene, RgC4H, from R. glutinosa was isolated and characterized. RgC4H has 86.34-93.89% amino acid sequence identity with the equivalent protein in other plants and localized to the endoplasmic reticulum. An association between the RgC4H expression and total phenolics content observed in non-transgenic and transgenic R. glutinosa plants suggests that this gene is involved in the process of phenolics biosynthesis. Furthermore, the tolerance of R. glutinosa to drought, salinity and H₂O₂ stresses was positively or negatively altered in plants with the overexpression or knockdown of RgC4H, respectively, as indicated by the analysis in some antioxidant physiological and molecular indices. Our study highlights the important role of RgC4H in the phenolics/phenylpropanoid pathway and reveals the involvement of phenolic-mediated regulation in oxidative stress tolerance in R. glutinosa.