Chapter 3 Biosynthesis of Terpenoid Indole Alkaloids in Catharanthus roseus Cells

Biosynthesis and Modulation of Terpenoid Indole Alkaloids in Catharanthus roseus: A Review of Targeting Genes and Secondary Metabolites

The medicinal plant C. roseus synthesizes biologically active alkaloids via the terpenoid indole alkaloid (TIAs) biosynthetic pathway. Most of these alkaloids have high therapeutic value, such as vinblastine and vincristine. Plant signaling components, plant hormones, precursors, growth hormones, prenylated proteins, and transcriptomic factors regulate the complex networks of TIA biosynthesis. For many years, researchers have been evaluating the scientific value of the TIA biosynthetic pathway and its potential in commercial applications for market opportunities. Metabolic engineering has revealed the major blocks in metabolic pathways regulated at the molecular level, unknown structures, metabolites, genes, enzyme expression, and regulatory genes. Conceptually, this information is necessary to create transgenic plants and microorganisms for the commercial production of high-value dimer alkaloids, such as vinca alkaloids, vinblastine, and vincristine In this review, we present current knowledge of the regulatory mechanisms of these components in the C. roseus TIA pathway, from genes to metabolites.

Metabolomics analysis reveals both plant variety and choice of hormone treatment modulate vinca alkaloid production in Catharanthus roseus

The medicinal plant Catharanthus roseus produces numerous secondary metabolites of interest for the treatment of many diseases - most notably for the terpene indole alkaloid (TIA) vinblastine, which is used in the treatment of leukemia and Hodgkin's lymphoma. Historically, methyl jasmonate (MeJA) has been used to induce TIA production, but in the past, this has only been investigated in whole seedlings, cell culture, or hairy root culture. This study examines the effects of the phytohormones MeJA and ethylene on the induction of TIA biosynthesis and accumulation in the shoots and roots of 8-day-old seedlings of two varieties of C. roseus. Using LCMS and RT-qPCR, we demonstrate the importance of variety selection, as we observe markedly different induction patterns of important TIA precursor compounds. Additionally, both phytohormone choice and concentration have significant effects on TIA biosynthesis. Finally, our study suggests that several early-induction pathway steps as well as pathway-specific genes are likely to be transcriptionally regulated. Our findings highlight the need for a complete set of'omics resources in commonly used C. roseus varieties and the need for caution when extrapolating results from one cultivar to another.

Novel method for improving ardicrenin content in hairy roots of Ardisia crenata Sims plants

To develop an alternative medicine related with taxol/camptothecin, a hairy roots induction system for measuring triterpenoid saponin ardicrenin was established. In the current study, mature and healthy seeds of Ardisia crenata plants were selected for obtaining aseptic seedlings. Two Agrobacterium rhizogenes strains ATCC 15834 and A4 were used to infect aseptic euphylla for inducing hairy roots of A. crenata plants. For the best combination of seeds germination, a Murashige-Skoog medium containing 1.0 mg L^-1 6-benzylaminopurine and 1.0 mg L^-1 naphthalene acetic acid was made, which reached a rate of 92.4 %. Results showed that ATCC 15834 and A4 both induced hairy roots of A. crenata for improving ardicrenin production. The PCR analysis demonstrated that ATCC 15834 and A4 Ri plasmid T-DNA had been successfully transferred and integrated into the genome of leaf cell nuclei, however the Vir region was not. Further, ardicrenin content in hairy roots ACHR 15834 8.2 %) induced by ATCC 15834 was quantified by the RP-HPLC, which was also 1.8-, 2.7-, 9.4- and 2.6-fold greater than those of ACHR 4 induced by A4 (4.5 %), ACR C formed by tissue culture (3.1 %), euphylla (0.8 %) and NR C formed nature (3.2 %), respectively. Taken together, hairy root lines of A. crenata obtained were able to express naturally more ardicrenin than natural plants.

Cloning and Overexpression of Strictosidine β-D-Glucosidase Gene Short Sequence from Catharanthus roseus in Escherichia coli

Purpose: Strictosidine-β-D-glucosidase (SGD) is considered as a key enzyme in the production of bisindole alkaloids in Catharanthus roseus. The present study illustrated the production of a short sequence of this enzyme in Escherichia coli without codon optimization.

Methods: Strictosidine-β-D-glucosidase (sgd) gene short sequence (1434 bp), which lacks the conserved sequence KGFFVWS and the localization peptide sequence at the C-terminal, was amplified from cDNA of C. roseus leaves, cloned and expressed in Escherichia coli. The activity of the produced protein in cell free lysate was tested using total alkaloid extract of C. roseus leaves.

Results: HPLC and LC-MS analysis of the assay mixture revealed the disappearance of the strictosidine peak.

Conclusion: SGD short sequence can be produced in Escherichia coli in active form without codon optimization.

CrERF5, an AP2/ERF Transcription Factor, Positively Regulates the Biosynthesis of Bisindole Alkaloids and Their Precursors in Catharanthus roseus

Catharanthus roseus contains a variety of monoterpenoid indole alkaloids (MIAs), among which bisindole alkaloids vinblastine and vincristine are well-known to have antitumor effects and widely used in clinical treatment. However, their contents in C. roseus is extremely low and difficult to meet market demands. Therefore, it is of great significance to study the transcriptional regulation mechanism of MIAs biosynthesis for high yielding of bisindole alkaloids in C. roseus. Studies have shown that MIAs biosynthesis in C. roseus has complex temporal and spacial specificity and is under tight transcriptional regulation, especially bisindole alkaloids. In this study, an AP2/ERF transcription factor CrERF5 was selected by RNA-seq of C. roseus organs, and its full-length sequence was cloned and characterized. CrERF5 responds to both ethylene and JA signals and is localized in the nucleus. CrERF5 could activate the transcriptional activity of the TDC promoter. Transient overexpressing CrERF5 in C. roseus petals caused a significant increase of the expression levels of key genes in both the upstream and downstream pathways of MIAs biosynthesis while silencing CrERF5 resulted in a decrease of them. Accordingly, the contents of bisindole alkaloids anhydrovinblastine and vinblastine, monoindole alkaloids ajmalicine, vindoline, and catharanthine were strongly enhanced in CrERF5-overexpressing petals while their contents decreased in CrERF5-silenced plants. These results suggested that CrERF5 is a novel positive ethylene-JA-inducible AP2/ERF transcription factor upregulating the MIAs biosynthetic pathway leading to the bisindole alkaloids accumulation.

Comparative transcriptome analysis of shoot and root tissue of Bacopa monnieri identifies potential genes related to triterpenoid saponin biosynthesis

Background

Bacopa monnieri commonly known as Brahmi is utilized in Ayurveda to improve memory and many other human health benefits. Bacosides enriched standardized extract of Bacopa monnieri is being marketed as a memory enhancing agent. In spite of its well known pharmacological properties it is not much studied in terms of transcripts involved in biosynthetic pathway and its regulation that controls the secondary metabolic pathway in this plant. The aim of this study was to identify the potential transcripts and provide a framework of identified transcripts involved in bacosides production through transcriptome assembly.

Results

We performed comparative transcriptome analysis of shoot and root tissue of Bacopa monnieri in two independent biological replicate and obtained 22.48 million and 22.0 million high quality processed reads in shoot and root respectively. After de novo assembly and quantitative assessment total 26,412 genes got annotated in root and 18,500 genes annotated in shoot sample. Quality of raw reads was determined by using SeqQC-V2.2. Assembled sequences were annotated using BLASTX against public database such as NR or UniProt. Searching against the KEGG pathway database indicated that 37,918 unigenes from root and 35,130 unigenes from shoot were mapped to 133 KEGG pathways. Based on the DGE data we found that most of the transcript related to CYP450s and UDP-glucosyltransferases were specifically upregulated in shoot tissue as compared to root tissue. Finally, we have selected 43 transcripts related to secondary metabolism including transcription factor families which are differentially expressed in shoot and root tissues were validated by qRT-PCR and their expression level were monitored after MeJA treatment and wounding for 1, 3 and 5 h.

Conclusions

This study not only represents the first de novo transcriptome analysis of Bacopa monnieri but also provides information about the identification, expression and differential tissues specific distribution of transcripts related to triterpenoid sapogenin which is one of the most important pharmacologically active secondary metabolite present in Bacopa monnieri. The identified transcripts in this study will establish a foundation for future studies related to carrying out the metabolic engineering for increasing the bacosides biosynthesis and its regulation for human health benefits.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3865-5) contains supplementary material, which is available to authorized users.

Proteome analysis of the medicinal plant Catharanthus roseus

A proteomic approach is undertaken aiming at the identification of novel proteins involved in the alkaloid biosynthesis of Catharanthus roseus. The C. roseus cell suspension culture A11 accumulates the terpenoid indole alkaloids strictosidine, ajmalicine and vindolinine. Cells were grown for 21 days, and alkaloid accumulation was monitored during this period. After a rapid increase between day 3 and day 6, the alkaloid content reached a maximum on day 16. Systematic analysis of the proteome was performed by two-dimensional polyacrylamide gel electrophoresis. After day 3, the proteome started to change with an increasing number of protein spots. On day 13, the proteome changed back to roughly the same as at the start of the growth cycle. 88 protein spots were selected for identification by mass spectrometry (MALDI-MS/MS). Of these, 58 were identified, including two isoforms of strictosidine synthase (EC 4.3.3.2), which catalyzes the formation of strictosidine in the alkaloid biosynthesis; tryptophan synthase (EC 4.1.1.28), which is needed for the supply of the alkaloid precursor tryptamine; 12-oxophytodienoate reductase, which is indirectly involved in the alkaloid biosynthesis as it catalyzes the last step in the biosynthesis of the regulator jasmonic acid. Unique sequences were found, which may also relate to unidentified biosynthetic proteins.

Biotechnological production of plant-based insecticides

The demand for natural and nonpersistent insecticides is increasing day by day. Plant cell cultures could be an alternative to conventional methods of production of insecticides from field-grown plants. In vitro cultured plant cells produce a wide array of insecticides as a part of their secondary metabolism. Their ability to synthesize key enzymes and the manipulation of these could lead to the enhanced production of many insecticides of industrial importance. The development of a high-yielding hairy root culture system for thiophenes, nicotine, and phytoecdysones is of considerable interest. In this article, the current literature on various factors that influence the growth, production, and secretion of six insecticidal compounds, namely, pyrethrins, azadirachtin, thiophenes, nicotine, rotenoids, and phytoecdysones which have been prospects for the scale-up of cell cultures, genetic engineering to obtain transgenic plants, and metabolically engineered plants for increased production of bio-molecules, has been discussed. Environmental safety clearance and the future prospects of application of biomolecules for plant-derived insecticides are presented.