Molecular cloning and functional characterization of UGTs from Glycyrrhiza uralensis flavonoid pathway

Root-specific flavones and critical enzyme genes involved in their synthesis changes due to drought stress on Scutellaria baicalensis

Introduction

Scutellaria baicalensis is rich in bioactive flavonoid, which are widely used in clinical therapy. Many environmental factors, such as water and temperature, affect gene expression and secondary metabolites accumulation in plants.

Methods

In this study, to explore the effect of drought stress on the accumulation of flavonoids and gene expression in S. baicalensis seedlings, 4-week-old Scutellaria baicalensis seedlings were treated with different concentrations of PEG6000 to simulate drought stress. The contents of four root-specific flavones (baicalein, wogonin, baicalin, and wogonoside) in samples under different treatments were quantitatively analyzed by high performance liquid chromatography (HPLC). The expression levels of flavonoid biosynthesis-related genes (PAL1, PAL2, CHS, and UBGAT) were determined by real-time quantitative PCR (qRT-PCR). Also, a correlation analysis between flavonoid contents and gene expression levels was made.

Results

The HPLC results revealed that 5 and 10% PEG6000 treatments significantly increased the content of four flavonoids, with 5% PEG 6000 treatment being the most beneficial to the flavonoids accumulation. The qRT-PCR results showed that PAL2 and CHS gene expressions differed significantly in different organs, while PAL1 and UBGAT had poor organ-specific. For genes in roots, the expression of PAL1 and UBGAT was the highest in 5% PEG6000 treatment, and PAL2 and CHS were the highest in 10% PEG6000 treatment. Compared with other concentrations of PEG6000, 5 and 10% PEG6000 were more advantageous for gene expression. Collectively, PEG6000 at a low concentration promoted the accumulation of flavonoids and the expression of related genes. Additionally, the correlation results demonstrated that PAL1, PAL2, CHS, and UBGAT genes in roots stimulated the formation and accumulation of the four flavonoids to varying degrees, while the exception of PAL2 gene expression in roots was negatively correlated with wogonin content.

Discussion

This study for the first time investigated the effect of drought stress on the downstream gene UBGAT in S.baicalensis seedlings as well as the correlation between gene expression and flavonoid content in S. baicalensis seedlings under drought stress, providing a new sight for studying the effects of drought stress on flavonoid accumulation and related gene expression in S. baicalensis.

Identification of novel peptide inhibitors for oncogenic KRAS G12D as therapeutic options using mutagenesis-based remodeling and MD simulations

The Kirsten rat sarcoma 2 viral oncogene homolog (KRAS) serves as a molecular switch, cycling between guanosine triphosphate (GTP)-bound and inactive guanosine diphosphate (GDP)-bound states. KRAS modulates numerous signal transduction pathways including the conventional RAF-MEK-ERK pathway. Mutations in the RAS genes have been linked to the formation of malignant tumors. Human malignancies typically show mutations in the Ras gene including HRAS, KRAS, and NRAS. Among all the mutations in exon 12 and exon 13 of the KRAS gene, the G12D mutation is more prevalent in pancreatic and lung cancer and accounts for around 41% of all G12 mutations, making them potential anticancer therapeutic targets. The present study is aimed at repurposing the peptide inhibitor KD2 of the KRAS G12D mutant. We employed an in-silico mutagenesis approach to design novel peptide inhibitors from the experimentally reported peptide inhibitor, and it was found that substitutions (N8W, N8I, and N8Y) might enhance the peptide's binding affinity toward the KRAS. Molecular dynamics simulations and binding energy calculations confirmed that the newly designed peptide inhibitors are stable and that their binding affinities are stronger as compared to the wild-type peptide. The detailed analysis revealed that newly designed peptides have the potential to inhibit KRAS/Raf interaction and the oncogenic signal of the KRAS G12D mutant. Our findings strongly suggest that these peptides should be tested and clinically validated to combat the oncogenic activity of KRAS.Communicated by Ramaswamy H. Sarma.

MALDI Imaging Assisted Discovery of a Di-O-glycosyltransferase from Platycodon grandiflorum Root

A matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) assisted genome mining strategy was developed for the discovery of glycosyltransferase (GT) from the root of Platycodon grandiflorum. A di-O-glycosyltransferase PgGT1 was discovered and characterized that is capable of catalyzing platycoside E (PE) synthesis through the attachment of two β-1,6-linked glucosyl residues sequentially to the glucosyl residue at the C3 position of platycodin D (PD). Although UDP-glucose is the preferred sugar donor for PgGT1, it could also utilize UDP-xylose and UDP-N-acetylglucosamine as weak donors. Residues S273, E274, and H350 played important roles in stabilizing the glucose donor and positioning the glucose in the optimal orientation for the glycosylation reaction. This study clarified two key steps involved in the biosynthetic pathway of PE and could greatly contribute to improving its industrial biotransformation.

Analysis of flavonoid metabolism during fruit development of Lycium chinense

Lycium chinense is an important medicinal plant in the northwest of China. Flavonoids are the major pharmacological components of L. chinense fruits. However, flavonoid metabolism during fruit development of L. chinense remains to be studied. Here, we analyzed the change of flavonoid contents, enzyme activity, and gene expression during fruit development of L. chinense. We found that flavonoids, anthocyanins, and catechins are the most important components of L. chinense fruits. Flavonoid content was increased with fruit development and was high at the late developmental stage. PAL, CHS, and F3H enzymes played a significant role in flavonoid accumulation in fruits. Transcriptomic analysis showed that anthocyanin pathway, flavonol pathway, flavonoid biosynthesis, and phenylpropanoid synthesis pathway were the major pathways involved in flavonoid metabolism in L. chinense. Gene expression analysis indicated that PAL1 and CHS2 genes were critical for flavonoid metabolism in L. chinense fruits. These discoveries help us understand the dynamic changes in flavonoids during fruit development and enhance the use of L. chinense fruits.

Functional characterization of a Colchicum autumnale L. double-bond reductase (CaDBR1) in colchicine biosynthesis

An alkenal double-bond reductase enzyme (CaDBR1) was cloned from Colchicum autumnale L. The encoded enzyme catalysed 4-coumaraldehyde to 4-hydroxydihydrocinnamaldehyde (4-HDCA). Its functional characterization increased the understanding of colchicine biosynthesis. As a traditional medical plant, Colchicum autumnale L. is famous for producing colchicine, a widely used drug for alleviating gout attacks. The biosynthetic pathway of colchicine was revealed most recently, and 4-hydroxydihydrocinnamaldehyde (4-HDCA) has been verified as a crucial intermediate derived from L-phenylalanine. However, the functional gene that catalyses the formation of 4-HDCA remains controversial. In this study, the alkenal double-bond reductase (DBR) gene member CaDBR1 was cloned and characterized from C. autumnale. Bioinformatics analysis predicted and characterized the basic physicochemical properties of CaDBR1. Recombinant CaDBR1 protein was heterologously expressed in Escherichia coli and purified by a Ni-NTA column. In vitro enzyme assays indicated that CaDBR1 could catalyse 4-coumaraldehyde to form 4-HDCA but could not generate 4-HDCA by taking cinnamaldehyde as a substrate. Stable transformation into tobacco BY-2 cells revealed that CaDBR1 localized in the cytoplasm, and tissue-specific expression results showed that CaDBR1 had the highest expression in bulbs. All these results verify and confirm the participation and contribution of CaDBR1 in the biosynthesis pathway of 4-HDCA and colchicine alkaloids in C. autumnale.

Screening and characterizing flavone synthases and its application in biosynthesizing vitexin from naringenin by a one-pot enzymatic cascade

C-glycosylated flavonoids are important structural derivatives of flavonoids and have a variety of physiological activities. Flavone synthase is a key enzyme for producing C-glycosylated flavonoids. In this study, three flavone synthase genes were cloned, overexpressed and characterized in E. coli. By analyzing the enzymatic properties of the enzymes, Aethusa cynapium flavone synthase (AcFNS) was better than Apium graveolens flavone synthase (AgFNS) and Petroselinum crispum flavone synthase (PcFNS) in terms of catalytic ability, organic solvent tolerance and stability. Then, a one-pot enzymatic cascade was developed to synthesize vitexin from naringenin by using AcFNS, C-glycosyltransferase (TcCGT) from Trollius chinensis, and sucrose synthase (GmSUS) from Glycine max. The effects of enzyme ratios, substrate concentrations, cofactors, and reaction conditions on vitexin production were determined. The highest vitexin production reached 935.6 mg/L with a corresponding molar conversion of 78.7 % for (2 S)-naringenin. Thus, this is the first report of a one-pot enzymatic cascade for vitexin production from naringenin in vitro.

Multi-omics analyses revealed key factors involved in fluorescent carbon-dots-regulated secondary metabolism in Tetrastigma hemsleyanum

BACKGROUND

Luminescent nanomaterials (LNMs), especially newly-exploited fluorescent carbon-dots (CDs), have demonstrated promising candidates for sunlight harvesting and enhanced photosynthesis efficiency of crops. However, most of the studies focus on the design and synthesis of LNMs and primary metabolism in biomass acceleration, secondary metabolism that closely associated with the quality ingredients of plants is rarely mentioned.

RESULTS

UV-absorptive and water-soluble NIR-CDs were harvested via a facile microwave-assisted carbonization method. The effect and regulatory mechanism of NIR-CDs on the secondary metabolism and bioactive ingredients accumulation in Tetrastigma hemsleyanum were explored. A total of 191 differential secondary metabolites and 6874 differentially expressed genes were identified when the NIR-CDs were adopted for enhancing growth of T. hemsleyanum. The phenolic acids were generally improved, but the flavonoids were more likely to decrease. The pivotal differentially expressed genes were involved in biosynthesis of secondary metabolites, flavonoid biosynthesis, porphyrin and chlorophyll metabolism, etc. The gene-metabolite association was constructed and 44 hub genes highly related to quality ingredients accumulation and growth were identified, among which and the top 5 genes of the PPI network might be the key regulators.

CONCLUSION

This research provided key regulatory genes and differentially accumulating quality ingredients under NIR-CDs-treatment, which could provide a theoretical basis for expanding the applications of nanomaterial in industrial crop agriculture.