Isolation and Functional Characterization of Multiple NADPH-Cytochrome P450 Reductase Genes from Camellia sinensis in View of Catechin Biosynthesis

Enhancing active ingredient biosynthesis in Chinese herbal medicine: biotechnological strategies and molecular mechanisms

Background

Chinese herbal medicine (CHM) is a fundamental component of traditional Chinese medical practice, offering a rich source of natural remedies with significant therapeutic potential. However, the scarcity of active ingredients and complex extraction procedures present substantial challenges to their widespread clinical application. This review aims to address this gap by exploring the potential of modern biotechnological advancements in enhancing the biosynthesis of these valuable compounds.

Methodology

The study takes a comprehensive approach, delving into the chemical composition of CHM's active ingredients and elucidating their biosynthetic pathways and molecular regulatory mechanisms. Additionally, it surveys recent progress in extraction methodologies and evaluates engineering strategies aimed at synthetic production. This multifaceted analysis forms the foundation for examining the role of synthetic biology in augmenting CHM's active ingredient synthesis.

Results

Our examination provides insights into the intricate biosynthetic pathways governing the formation of CHM's active ingredients, as well as the complex molecular regulatory networks that underlie these processes. Furthermore, the review highlights advancements in extraction techniques, demonstrating their ability to streamline and enhance the isolation of these compounds. Engineering approaches for synthetic production, including metabolic engineering and synthetic biology tools, are assessed for their potential to overcome natural limitations and scale up production.

Conclusions

By integrating insights from biosynthesis, molecular regulation, extraction methodologies, and synthetic biology, this review establishes a robust theoretical framework for enhancing the production of CHM's active ingredients. The proposed strategies and practical guidance aim to facilitate their broader utilization in modern medicine while promoting sustainability and accessibility within this invaluable medicinal heritage.

Identification of a Flavanone 2-Hydroxylase Involved in Flavone C-Glycoside Biosynthesis from Camellia sinensis

Tea contains a variety of flavone C-glycosides, which are important compounds that distinguish tea cultivars and tea categories. However, the biosynthesis pathway of flavone C-glycosides in tea plant remains unknown, and the key enzymes involved have not been characterized. In this study, a liquid chromatography-mass spectrometry method to determine 9 flavone C-glycosides was developed, and the accumulation patterns of 9 flavone C-glycosides in tea plants were examined first. Then, an entry enzyme CsF2H for flavone C-glycoside biosynthesis was identified, which had four cytochrome P450-specific conserved motifs and was targeted to the endoplasmic reticulum. Correlation analysis indicated that the expression level of CsF2H was positively correlated with all contents of 9 flavone C-glycosides. The recombinant CsF2H could convert flavanone (naringenin) into the corresponding 2-hydroxyflavonone (2-hydroxynaringenin), rather than into flavone (apigenin). Heterologous coexpression of CsF2H and CsCGT1 in yeast revealed that the substrate naringenin could be enzymatically converted to flavone mono-C-glycosides vitexin and isovitexin under the catalytic control of CsF2H and CsCGT1 following dehydration. Gene-specific antisense oligonucleotide analysis suggested that suppressing CsF2H significantly reduced the levels of 9 flavone C-glycosides. Together, CsF2H is the first key enzyme that generates flavone C-glycosides through the 2-hydroxyflavanone biosynthesis pathway in tea plants.

A flavonoid metabolon: cytochrome b5 enhances B-ring trihydroxylated flavan-3-ols synthesis in tea plants

Flavan-3-ols are prominent phenolic compounds found abundantly in the young leaves of tea plants. The enzymes involved in flavan-3-ol biosynthesis in tea plants have been extensively investigated. However, the localization and associations of these numerous functional enzymes within cells have been largely neglected. In this study, we aimed to investigate the synthesis of flavan-3-ols in tea plants, particularly focusing on epigallocatechin gallate. Our analysis involving the DESI-MSI method to reveal a distinct distribution pattern of B-ring trihydroxylated flavonoids, primarily concentrated in the outer layer of buds. Subcellular localization showed that CsC4H, CsF3'H, and CsF3'5'H localizes endoplasmic reticulum. Protein-protein interaction studies demonstrated direct associations between CsC4H, CsF3'H, and cytoplasmic enzymes (CHS, CHI, F3H, DFR, FLS, and ANR), highlighting their interactions within the biosynthetic pathway. Notably, CsF3'5'H, the enzyme for B-ring trihydroxylation, did not directly interact with other enzymes. We identified cytochrome b5 isoform C serving as an essential redox partner, ensuring the proper functioning of CsF3'5'H. Our findings suggest the existence of distinct modules governing the synthesis of different B-ring hydroxylation compounds. This study provides valuable insights into the mechanisms underlying flavonoid diversity and efficient synthesis and enhances our understanding of the substantial accumulation of B-ring trihydroxylated flavan-3-ols in tea plants.

Mining and functional characterization of NADPH-cytochrome P450 reductases of the DNJ biosynthetic pathway in mulberry leaves

BACKGROUND

1-Deoxynojirimycin (DNJ), the main active ingredient in mulberry leaves, with wide applications in the medicine and food industries due to its significant functions in lowering blood sugar, and lipids, and combating viral infections. Cytochrome P450 is a key enzyme for DNJ biosynthesis, its activity depends on the electron supply of NADPH-cytochrome P450 reductases (CPRs). However, the gene for MaCPRs in mulberry leaves remains unknown.

RESULTS

In this study, we successfully cloned and functionally characterized two key genes, MaCPR1 and MaCPR2, based on the transcriptional profile of mulberry leaves. The MaCPR1 gene comprised 2064 bp, with its open reading frame (ORF) encoding 687 amino acids. The MaCPR2 gene comprised 2148 bp, and its ORF encoding 715 amino acids. The phylogenetic tree indicates that MaCPR1 and MaCPR2 belong to Class I and Class II, respectively. In vitro, we found that the recombinant enzymes MaCPR2 protein could reduce cytochrome c and ferricyanide using NADPH as an electron donor, while MaCPR1 did not. In yeast, heterologous co-expression indicates that MaCPR2 delivers electrons to MaC3'H hydroxylase, a key enzyme catalyzing the production of chlorogenic acid from 3-O-p-coumaroylquinic acid.

CONCLUSIONS

These findings highlight the orchestration of hydroxylation process mediated by MaCPR2 during the biosynthesis of secondary metabolite biosynthesis in mulberry leaves. These results provided a foundational understanding for fully elucidating the DNJ biosynthetic pathway within mulberry leaves.

Class I and II NADPH-cytochrome P450 reductases exhibit different roles in triterpenoid biosynthesis in Lotus japonicus

Cytochrome P450 monooxygenases (CYPs) are enzymes that play critical roles in the structural diversification of triterpenoids. To perform site-specific oxidations of the triterpene scaffold, CYPs require electrons transferred by NADPH-cytochrome P450 reductase (CPR), which is classified into two main classes, class I and class II, based on their structural difference. Lotus japonicus is a triterpenoids-producing model legume with one CPR class I gene (LjCPR1) and a minimum of two CPR class II genes (LjCPR2-1 and LjCPR2-2). CPR classes I and II from different plants have been reported to be involved in different metabolic pathways. By performing gene expression analyses of L. japonicus hairy root culture treated with methyl jasmonate (MeJA), this study revealed that LjCPR1, CYP716A51, and LUS were down-regulated which resulted in no change in betulinic acid and lupeol content. In contrast, LjCPR2s, bAS, CYP93E1, and CYP72A61 were significantly upregulated by MeJA treatment, followed by a significant increase of the precursors for soyasaponins, i.e. β-amyrin, 24-OH β-amyrin, and sophoradiol content. Triterpenoids profile analysis of LORE1 insertion and hairy root mutants showed that the loss of the Ljcpr2-1 gene significantly reduced soyasaponins precursors but not in Ljcpr1 mutants. However, Ljcpr1 and Ljcpr2-1 mutants showed a significant reduction in lupeol and oleanolic, ursolic, and betulinic acid contents. Furthermore, LjCPR1, but not LjCPR2, was crucial for seed development, supporting the previous notion that CPR class I might support plant basal metabolism. This study suggests that CPR classes I and II play different roles in L. japonicus triterpenoid biosynthesis.