Advances in the Regulation of In Vitro Paclitaxel Production: Methylation of a Y-Patch Promoter Region Alters BAPT Gene Expression in Taxus Cell Cultures

Mass Spectrometry-Imaging Analysis of Active Ingredients in the Leaves of Taxus cuspidata

BACKGROUND

Taxus cuspidata is an endangered evergreen conifer mainly found in Northeast Asia. In addition to the well-known taxanes, several active ingredients were detected in the leaves of T. cuspidata. However, the precise spatial distribution of active ingredients in the leaves of T. cuspidata is largely unknown.

RESULTS

in the present study, timsTOF flex MALDI-2 analysis was used to uncover the accumulation pattern of active ingredients in T. cuspidata leaves. In total, 3084 ion features were obtained, of which 944 were annotated according to the mass spectrometry database. The principal component analysis separated all of the detected metabolites into four typical leaf tissues: mesophyll cells, upper epidermis, lower epidermis, and vascular bundle cells. Imaging analysis identified several leaf tissues that specifically accumulated active ingredients, providing theoretical support for studying the regulation mechanism of compound biosynthesis. Furthermore, the relative accumulation levels of each identified compound were analyzed. Two flavonoid compounds, ligustroflavone and Morin, were identified with high content through quantitative analysis of the ion intensity.

CONCLUSIONS

our data provides fundamental information for the protective utilization of T. cuspidata.

Targeted control of supporting pathways in paclitaxel biosynthesis with CRISPR-guided methylation

Introduction: Plant cell culture biomanufacturing is rapidly becoming an effective strategy for production of high-value plant natural products, such as therapeutic proteins and small molecules, vaccine adjuvants, and nutraceuticals. Many of these plant natural products are synthesized from diverse molecular building blocks sourced from different metabolic pathways. Even so, engineering approaches for increasing plant natural product biosynthesis have typically focused on the core biosynthetic pathway rather than the supporting pathways. Methods: Here, we use both CRISPR-guided DNA methylation and chemical inhibitors to control flux through the phenylpropanoid pathway in Taxus chinensis, which contributes a phenylalanine derivative to the biosynthesis of paclitaxel (Taxol), a potent anticancer drug. To inhibit PAL, the first committed step in phenylpropanoid biosynthesis, we knocked down expression of PAL in Taxus chinensis plant cell cultures using a CRISPR-guided plant DNA methyltransferase (NtDRM). For chemical inhibition of downstream steps in the pathway, we treated Taxus chinensis plant cell cultures with piperonylic acid and caffeic acid, which inhibit the second and third committed steps in phenylpropanoid biosynthesis: cinnamate 4-hydroxylase (C4H) and 4-coumaroyl-CoA ligase (4CL), respectively. Results: Knockdown of PAL through CRISPR-guided DNA methylation resulted in a profound 25-fold increase in paclitaxel accumulation. Further, through the synergistic action of both chemical inhibitors and precursor feeding of exogenous phenylalanine, we achieve a 3.5-fold increase in paclitaxel biosynthesis and a similar reduction in production of total flavonoids and phenolics. We also observed perturbations to both activity and expression of PAL, illustrating the complex transcriptional co-regulation of these first three pathway steps. Discussion: These results highlight the importance of controlling the metabolic flux of supporting pathways in natural product biosynthesis and pioneers CRISPR-guided methylation as an effective method for metabolic engineering in plant cell cultures. Ultimately, this work demonstrates a powerful method for rewiring plant cell culture systems into next-generation chassis for production of societally valuable compounds.

Advances in DNA methylation and demethylation in medicinal plants: a review

DNA methylation and demethylation are widely acknowledged epigenetic phenomena which can cause heritable and phenotypic changes in functional genes without changing the DNA sequence. They can thus affect phenotype formation in medicinal plants. However, a comprehensive review of the literature summarizing current research trends in this field is lacking. Thus, this review aims to provide an up-to-date summary of current methods for the detection of 5-mC DNA methylation, identification and analysis of DNA methyltransferases and demethyltransferases, and regulation of DNA methylation in medicinal plants. The data showed that polyploidy and environmental changes can affect DNA methylation levels in medicinal plants. Changes in DNA methylation can thus regulate plant morphogenesis, growth and development, and formation of secondary metabolites. Future research is required to explore the mechanisms by which DNA methylation regulates the accumulation of secondary metabolites in medicinal plants.

Insights into the control of taxane metabolism: Molecular, cellular, and metabolic changes induced by elicitation in Taxus baccata cell suspensions

More knowledge is needed about the molecular/cellular control of paclitaxel (PTX) production in Taxus spp. cell cultures. In this study, the yield of this anticancer agent in Taxus baccata cell suspensions was improved 11-fold after elicitation with coronatine (COR) compared to the untreated cells, and 18-fold when co-supplemented with methyl-β-cyclodextrins (β-CDs). In the dual treatment, the release of taxanes from the producer cells was greatly enhanced, with 81.6% of the total taxane content being found in the medium at the end of the experiment. The experimental conditions that caused the highest PTX production also induced its maximum excretion, and increased the expression of taxane biosynthetic genes, especially the flux-limiting BAPT and DBTNBT. The application of COR, which activates PTX biosynthesis, together with β - CDs, which form inclusion complexes with PTX and related taxanes, is evidently an efficient strategy for enhancing PTX production and release to the culture medium. Due to the recently described role of lipid droplets (LDs) in the trafficking and accumulation of hydrophobic taxanes in Taxus spp. cell cultures, the structure, number and taxane storage capacity of these organelles was also studied. In elicited cultures, the number of LDs increased and they mainly accumulated taxanes with a side chain, especially PTX. Thus, PTX constituted up to 50-70% of the total taxanes found in LDs throughout the experiment in the COR + β - CD-treated cultures. These results confirm that LDs can store taxanes and distribute them inside and outside cells.

The Epigenetic Regulation in Plant Specialized Metabolism: DNA Methylation Limits Paclitaxel in vitro Biotechnological Production

Environmental conditions are key factors in the modulation of the epigenetic mechanisms regulating gene expression in plants. Specifically, the maintenance of cell cultures in optimal in vitro conditions alters methylation patterns and, consequently, their genetic transcription and metabolism. Paclitaxel production in Taxus x media cell cultures is reduced during its maintenance in in vitro conditions, compromising the biotechnological production of this valuable anticancer agent. To understand how DNA methylation influences taxane production, the promoters of three genes (GGPPS, TXS, and DBTNBT) involved in taxane biosynthesis have been studied, comparing the methylation patterns between a new line and one of ~14 years old. Our work revealed that while the central promoter of the GGPPS gene is protected from cytosine methylation accumulation, TXS and DBTNBT promoters accumulate methylation at different levels. The DBTNBT promoter of the old line is the most affected, showing a 200 bp regulatory region where all the cytosines were methylated. This evidence the existence of specific epigenetic regulatory mechanisms affecting the last steps of the pathway, such as the DBTNBT promoter. Interestingly, the GGPPS promoter, a regulatory sequence of a non-specific taxane biosynthetic gene, was not affected by this mechanism. In addition, the relationship between the detected methylation points and the predicted transcription factor binding sites (TFBS) showed that the action of TFs would be compromised in the old line, giving a further explanation for the production reduction in in vitro cell cultures. This knowledge could help in designing novel strategies to enhance the biotechnological production of taxanes over time.

Application of Priming Strategy for Enhanced Paclitaxel Biosynthesis in Taxus × Media Hairy Root Cultures

Despite huge progress in biotechnological approaches to paclitaxel production, Taxus spp. in vitro culture productivity still remains a challenge. This could be solved by developing a new strategy engaging mechanisms of the primed defence response joined with subsequent elicitation treatment to circumvent limitations in paclitaxel biosynthesis. The hairy roots were primed by preincubation with β-aminobutyric acid (BABA) for 24 h or 1 week, and then elicited with methyl jasmonate (MeJA) or a mixture of MeJA, sodium nitroprusside and L-phenylalanine (MIX). The effect of priming was evaluated on a molecular level by examination of the expression profiles of the four genes involved in paclitaxel biosynthesis, i.e., TXS (taxadiene synthase), BAPT (baccatin III: 3-amino, 3-phenylpropanoyltransferase), DBTNBT (3′-N-debenzoyl-2-deoxytaxol-N-benzoyltransferase) and PAM (phenylalanine aminomutase), as well as rolC (cytokinin-β-glucosidase), originated from the T-DNA of Agrobacterium rhizogenes. The maximum paclitaxel yield was achieved in cultures primed with BABA for 1 week and elicited with MIX (3179.9 ± 212 µg/g dry weight), which corresponded to the highest expression levels of TXS and BAPT genes. Although BABA itself induced the investigated gene expression over control level, it was not translated into paclitaxel production. Nevertheless, preincubation with BABA essentially affected paclitaxel yield, and the duration of BABA pretreatment seemed to have the most pronounced impact on its productivity.

Identification and in-silico characterization of taxadien-5α-ol-O-acetyltransferase (TDAT) gene in Corylus avellana L

Paclitaxel^® (PC) is one of the most effective and profitable anti-cancer drugs. The most promising sources of this compound are natural materials such as tissue cultures of Taxus species and, more recently, hazelnut (Corylus avellana L.). A large part of the PC biosynthetic pathway in the yew tree and a few steps in the hazelnut have been identified. Since understanding the biosynthetic pathway of plant-based medicinal metabolites is an effective step toward their development and engineering, this paper aimed to identify taxadiene-5α-ol-O-acetyltransferase (TDAT) in hazelnut. TDAT is one of the key genes involved in the third step of the PC biosynthetic pathway. In this study, the TDAT gene was isolated using the nested-PCR method and then characterized. The cotyledon-derived cell mass induced with 150 μM of methyl jasmonate (MeJA) was utilized to isolate RNA and synthesize the first-strand cDNA. The full-length cDNA of TDAT is 1423 bp long and contains a 1302 bp ORF encoding 433 amino acids. The phylogenetic analysis of this gene revealed high homology with its ortholog genes in Quercus suber and Juglans regia. Bioinformatics analyses were used to predict the secondary and tertiary structures of the protein. Due to the lack of signal peptide, protein structure prediction suggested that this protein may operate at the cytoplasm. The homologous superfamily of the T5AT protein, encoded by TDAT, has two domains. The highest and lowest hydrophobicity of amino acids were found in proline 142 and lysine 56, respectively. T5AT protein fragment had 24 hydrophobic regions. The tertiary structure of this protein was designed using Modeler software (V.9.20), and its structure was verified based on the results of the Verify3D (89.46%) and ERRAT (90.3061) programs. The T5AT enzyme belongs to the superfamily of the transferase, and the amino acids histidine 164, cysteine 165, leucine 166, histidine 167, and Aspartic acid 168 resided at its active site. More characteristics of TDAT, which would aid PC engineering programs and maximize its production in hazelnut, were discussed.

Genomic methylation in plant cell cultures: A barrier to the development of commercial long-term biofactories

Plant cell biofactories offer great advantages for the production of plant compounds of interest, although certain limitations still need to be overcome before their maximum potential is reached. One obstacle is the gradual loss of secondary metabolite production during in vitro culture maintenance, which is an important impediment in the development of large-scale production systems. The relationship between in vitro maintenance and epigenetic changes has been demonstrated in several plant species; in particular, methylation levels have been found to increase in in vitro cultures over time. Higher DNA methylation levels have been correlated with a low yield of secondary metabolites in in vitro plant cell cultures. The longer the period of subculturing, the more methylated cytosines were found throughout the genome, and secondary metabolism decreased significantly. This review summarizes different studies on epigenetic changes during the maintenance of in vitro cell cultures and the insights they provide on the mechanisms involved. It concludes by looking at the perspectives for new approaches designed to avoid declines in metabolite production.

In Vitro Study of the Anticancer Effects of Biotechnological Extracts of the Endangered Plant Species Satureja Khuzistanica

Many medicinal plant species are currently threatened in their natural habitats because of the growing demand for phytochemicals worldwide. A sustainable alternative for the production of bioactive plant compounds are plant biofactories based on cell cultures and organs. In addition, plant extracts from biofactories have significant advantages over those obtained from plants, since they are free of contamination by microorganisms, herbicides and pesticides, and they provide more stable levels of active ingredients. In this context, we report the establishment of Satureja khuzistanica cell cultures able to produce high amounts of rosmarinic acid (RA). The production of this phytopharmaceutical was increased when the cultures were elicited with coronatine and scaled up to a benchtop bioreactor. S. khuzistanica extracts enriched in RA were found to reduce the viability of cancer cell lines, increasing the sub-G0/G1 cell population and the activity of caspase-8 in MCF-7 cells, which suggest that S. khuzistanica extracts can induce apoptosis of MCF-7 cells through activation of the extrinsic pathway. In addition, our findings indicate that other compounds in S. khuzistanica extracts may act synergistically to potentiate the anticancer activity of RA.