Promoter analysis of the Catharanthus roseus geraniol 10-hydroxylase gene involved in terpenoid indole alkaloid biosynthesis

Effect of the plant probiotic bacteria on terpenoid indole alkaloid biosynthesis pathway gene expression profiling, vinblastine and vincristine content in the root of Catharanthus roseus

BACKGROUND

Catharanthus roseus is the sole resource of vinblastine and vincristine, two TIAs of great interest for their powerful anticancer activities. Increasing the concentration of these alkaloids in various organs of the plant is one of the important goals in C. roseus breeding programs. Plant probiotic bacteria (PBB) act as biotic elicitors and can induce the synthesis of secondary products in plants. The purpose of this research is to study the effects of PBB on expression of the TIA biosynthetic pathway genes and the content of alkaloids in C. roseus.

METHODS AND RESULTS

The individual and combined effects of P. fluorescens strains 169 and A. brasilense strains Ab-101 was studied for expression of the TIA biosynthetic pathway genes (G10H, DAT, T16H and CrPRX) using qRT-PCR and the content of vinblastine and vincristine using HPLC method in roots of C. roseus. P. fluorescens. This drastically increased the content of vinblastine and vincristine alkaloids, compared to the control in the roots, to 174 and 589 (µg/g), respectively. Molecular analysis showed bacterium significantly increased the expression of more genes in the TIA biosynthetic pathway compared to the control. P. fluorescens increased the expression of the final gene of the biosynthetic pathway (CrPRX) 47.9 times compared to the control. Our findings indicate the correlation between transcriptional and metabolic outcomes. The same was true for A. brasilense.

CONCLUSIONS

It can be concluded that seed treatments and seedling root treatments composed of naturally occurring probiotic bacteria are likely to be widely applicable for inducing enhanced alkaloid contents in medicinal plants.

Arabidopsis ABSCISIC ACID INSENSITIVE4 targets PROTEIN L-ISOASPARTYL METHYLTRANSFERASE1 in seed

Arabidopsis ABSCISIC ACID INSENSITIVE4 (ABI4) positively regulates the protein repairing enzyme (PRE) PROTEIN L-ISOASPARTYL METHYLTRANSFERASE1 (PIMT1) in seed for its implication in seed vigor and longevity. PROTEIN L-ISOASPARTYL METHYLTRANSFERASE (PIMT) is a protein repairing enzyme (PRE) and is implicated in seed vigor and longevity. PIMT has been shown to be induced by ABA, however, its detailed regulation by ABA signaling components is unknown. Herein, we report that ABSCISIC ACID INSENSITIVE4 (ABI4) directly binds to the PIMT1 promoter and regulates its expression in Arabidopsis seeds. AtPIMT1 promoter analysis demonstrated the presence of putative ABI4 binding sites. Our Y1H analysis revealed that AtABI4 transcription factor binds to the AtPIMT1 promoter. Dual luciferase assay also demonstrated the binding of the AtABI4 transcription factor to the AtPIMT1 promoter. Subsequently, we have generated AtPIMT1 promoter GUS lines and revealed that ABA induced expression of GUS in Arabidopsis thaliana. Expression analyses exhibited reduced accumulation of PIMT1 protein and transcript with significant reduction in total PIMT activity in abi4-1 mutants as compared to that of the wild type. The AtPIMT1 promoter GUS expression in abi4-1 mutants was also found to be severely affected in both the control and ABA treatment. Hence, through molecular and genetic evidences we show that the AtABI4 plays a central role in regulating the expression of AtPIMT1 to impart seed vigor and longevity to orthodox seeds.

Identification and Characterization of Transcription Factors Regulating Terpenoid Indole Alkaloid Biosynthesis in Catharanthus roseus

Biosynthesis of the therapeutically valuable terpenoid indole alkaloids (TIAs), in the medicinal plant Catharanthus roseus, is one of the most elaborate and complex metabolic processes. Although genomic and transcriptomic resources have significantly accelerated gene discovery in the TIA pathway, relatively few genes of transcription factors (TFs) have been identified and characterized thus far. Systematic identification of TFs and elucidation of their functions are crucial for understanding TIA pathway regulation. The successful discovery of TFs in the TIA pathway has relied mostly on three different approaches, (1) identification of cis-regulatory motifs (CRMs) present in the pathway gene promoters as they often provide clues on potential TFs that bind to the promoters, (2) co-expression analysis, based on the assumption that TFs regulating a metabolic or developmental pathway exhibit similar spatiotemporal expression as the pathway genes, and (3) isolation of homologs of TFs known to regulate structurally similar or diverse specialized metabolites in different plant species. TFs regulating TIA pathway have been isolated using either an individual or a combination of the three approaches. Here we describe transcriptome-based coexpression analysis and cis-element determination to identify TFs in C. roseus. In addition, we describe the protocols for generation of transgenic hairy roots, Agrobacterium infiltration of flowers, and electrophoretic mobility shift assay (EMSA). The methods described here are useful for the identification and characterization of potential TFs involved in the regulation of special metabolism in other medicinal plants.

Identification and characterization of SlbHLH, SlDof and SlWRKY transcription factors interacting with SlDPD gene involved in costunolide biosynthesis in Saussurea lappa

The genes involved in costunolide biosynthesis in Saussurea lappa have been identified recently by our lab. However, the study of transcriptional regulators of these genes was lacking for better opportunities for engineering the pharmacologically important biosynthetic pathway. Therefore, we cloned the promoter region of diphosphomevalonate decarboxylase gene (DPD) and analyzed its cis-acting regulatory elements to reveal the potential transcription factor (TF) binding sites for Dof, bHLH and WRKY family proteins in the gene promoter. The transcriptome study approach followed by the hidden Markov model based search, digital gene expression, co-expression network analysis, conserved domain properties and evolutionary analyses were carried out to screen out seven putative TFs for the DPD-TF interaction studies. Yeast one-hybrid assays were performed and three TFs were reported, namely, SlDOF2, SlbHLH3 and SlWRKY2 from Dof, bHLH and WRKY families, respectively that interacted positively with the DPD gene of the costunolide biosynthetic pathway. The tissue specific relative gene expression studies also supported the linked co-expression of the gene and its interacting TFs The present report will improve the understanding of transcriptional regulation pattern of costunolide biosynthetic pathway.

BHLH IRIDOID SYNTHESIS 3 is a member of a bHLH gene cluster regulating terpenoid indole alkaloid biosynthesis in Catharanthus roseus

Basic helix-loop-helix (bHLH) transcription factors (TFs) are key regulators of plant specialized metabolites, including terpenoid indole alkaloids (TIAs) in Catharanthus roseus. Two previously characterized subgroup-IVa bHLH TFs, BIS1 (bHLH Iridoid Synthesis 1) and BIS2 regulate iridoid biosynthesis in the TIA pathway. We reanalyzed the recently updated C. roseus genome sequence and discovered that BIS1 and BIS2 are clustered on the same genomic scaffold with a previously uncharacterized bHLH gene, designated as BIS3. Only a few bHLH gene clusters have been studied to date. Comparative analysis of 49 genome sequences from different plant lineages revealed the presence of analogous bHLH clusters in core angiosperms, including the medicinal plants Calotropis gigantea (giant milkweed) and Gelsemium sempervirens (yellow jessamine), but not in the analyzed basal angiosperm and lower plants. Similar to the iridoid pathway genes, BIS3 is highly expressed in roots and induced by methyl jasmonate. BIS3 activates the promoters of iridoid branch genes, geraniol synthase (GES), geraniol 10-hydroxylase (G10H), 8-hydroxygeraniol oxidoreductase (8HGO), iridoid synthase (IS), 7-deoxyloganetic acid glucosyl transferase (7-DLGT), and 7-deoxyloganic acid hydroxylase (7DLH), but not iridoid oxidase (IO). Transactivation of the promoters was abolished when BIS3 is converted to a dominant repressor by fusing with the ERF-associated amphiphilic repression (EAR) sequence. In addition, BIS3 acts synergistically with BIS1 and BIS2 to activate the G10H promoter in tobacco cells. Mutation of the known bHLH TF binding motif, G-box (CACGTG) in the G10H promoter significantly reduced but did not abolish the transactivation by BIS3. Promoter deletion analysis of G10H suggests that the sequences adjacent to the G-box are also involved in the regulation by BIS3. Overexpression of BIS3 in C. roseus flower petals significantly upregulated the expression of iridoid biosynthetic genes and increased loganic acid accumulation. BIS2 expression was significantly induced by BIS3 although BIS3 did not directly activate the BIS2 promoter. Our results advance our understanding of the regulation of plant specialized metabolites by bHLH TF clusters.

Revisiting the ORCA gene cluster that regulates terpenoid indole alkaloid biosynthesis in Catharanthus roseus

Transcription factor (TF) gene clusters in plants, such as tomato, potato, petunia, tobacco, and almond, have been characterized for their roles in the biosynthesis of diverse array of specialized metabolites. In Catharanthus roseus, three AP2/ERF TFs, ORCA3, ORCA4, and ORCA5, have been shown to be present on the same genomic scaffold, forming a cluster that regulates the biosynthesis of pharmaceutically important terpenoid indole alkaloids (TIAs). Our analysis of the recently updated C. roseus genome sequence revealed that the ORCA cluster comprises two additional AP2/ERFs, the previously characterized ORCA2 and a newly identified member designated as ORCA6. Transcriptomic analysis revealed that the ORCAs are highly expressed in stems, followed by leaves, roots and flowers. Expression of ORCAs was differentially induced in response to methyl-jasmonate and ethylene treatment. In addition, ORCA6 activated the strictosidine synthase (STR) promoter in tobacco cells. Activation of the STR promoter was significantly higher when ORCA2 or ORCA6 was coexpressed with the mitogen-activated protein kinase kinase, CrMPKK1. Furthermore, transient overexpression of ORCA6 in C. roseus flower petals activated TIA pathway gene expression and TIA accumulation. The results described here advance our understanding of regulation of TIA pathway by the ORCA gene cluster and the evolution for plant ERF gene clusters.

Cross-family transcription factor interaction between MYC2 and GBFs modulates terpenoid indole alkaloid biosynthesis

Biosynthesis of medicinally valuable terpenoid indole alkaloids (TIAs) in Catharanthus roseus is regulated by transcriptional activators such as the basic helix-loop-helix factor CrMYC2. However, the transactivation effects are often buffered by repressors, such as the bZIP factors CrGBF1 and CrGBF2, possibly to fine-tune the accumulation of cytotoxic TIAs. Questions remain as to whether and how these factors interact to modulate TIA production. We demonstrated that overexpression of CrMYC2 induces CrGBF expression and results in reduced alkaloid accumulation in C. roseus hairy roots. We found that CrGBF1 and CrGBF2 form homo- and heterodimers to repress the transcriptional activities of key TIA pathway gene promoters. We showed that CrGBFs dimerize with CrMYC2, and CrGBF1 binds to the same cis-elements (T/G-box) as CrMYC2 in the target gene promoters. Our findings suggest that CrGBFs antagonize CrMYC2 transactivation possibly by competitive binding to the T/G-box in the target promoters and/or protein-protein interaction that forms a non-DNA binding complex that prevents CrMYC2 from binding to its target promoters. Homo- and heterodimer formation allows fine-tuning of the amplitude of TIA gene expression. Our findings reveal a previously undescribed regulatory mechanism that governs the TIA pathway genes to balance metabolic flux for TIA production in C. roseus.

A differentially regulated AP2/ERF transcription factor gene cluster acts downstream of a MAP kinase cascade to modulate terpenoid indole alkaloid biosynthesis in Catharanthus roseus

Catharanthus roseus produces bioactive terpenoid indole alkaloids (TIAs), including the chemotherapeutics, vincristine and vinblastine. Transcriptional regulation of TIA biosynthesis is not fully understood. The jasmonic acid (JA)-responsive AP2/ERF transcription factor (TF), ORCA3, and its regulator, CrMYC2, play key roles in TIA biosynthesis. ORCA3 forms a physical cluster with two uncharacterized AP2/ERFs, ORCA4 and 5. Here, we report that (1) the ORCA gene cluster is differentially regulated; (2) ORCA4, while overlapping functionally with ORCA3, modulates an additional set of TIA genes. Unlike ORCA3, ORCA4 overexpression resulted in dramatic increase of TIA accumulation in C. roseus hairy roots. In addition, CrMYC2 is capable of activating ORCA3 and co-regulating TIA pathway genes concomitantly with ORCA3. The ORCA gene cluster and CrMYC2 act downstream of a MAP kinase cascade that includes a previously uncharacterized MAP kinase kinase, CrMAPKK1. Overexpression of CrMAPKK1 in C. roseus hairy roots upregulated TIA pathways genes and increased TIA accumulation. This work provides detailed characterization of a TF gene cluster and advances our understanding of the transcriptional and post-translational regulatory mechanisms that govern TIA biosynthesis in C. roseus.

The basic helix-loop-helix transcription factor BIS2 is essential for monoterpenoid indole alkaloid production in the medicinal plant Catharanthus roseus

Monoterpenoid indole alkaloids (MIAs) are produced as plant defence compounds. In the medicinal plant Catharanthus roseus, they comprise the anticancer compounds vinblastine and vincristine. The iridoid (monoterpenoid) pathway forms one of the two branches that feed MIA biosynthesis and its activation is regulated by the transcription factor (TF) basic helix-loop-helix (bHLH) iridoid synthesis 1 (BIS1). Here, we describe the identification and characterisation of BIS2, a jasmonate (JA)-responsive bHLH TF expressed preferentially in internal phloem-associated parenchyma cells, which transactivates promoters of iridoid biosynthesis genes and can homodimerise or form heterodimers with BIS1. Stable overexpression of BIS2 in C. roseus suspension cells and transient ectopic expression of BIS2 in C. roseus petal limbs resulted in increased transcript accumulation of methylerythritol-4-phosphate and iridoid pathway genes, but not of other MIA genes or triterpenoid genes. Transcript profiling also indicated that BIS2 expression is part of an amplification loop, as it is induced by overexpression of either BIS1 or BIS2. Accordingly, silencing of BIS2 in C. roseus suspension cells completely abolished the JA-induced upregulation of the iridoid pathway genes and subsequent MIA accumulation, despite the presence of induced BIS1, indicating that BIS2 is essential for MIA production in C. roseus.

Engineering overexpression of ORCA3 and strictosidine glucosidase in Catharanthus roseus hairy roots increases alkaloid production

Catharanthus roseus produces many pharmaceutically important terpenoid indole alkaloids (TIAs) such as vinblastine, vincristine, ajmalicine, and serpentine. Past metabolic engineering efforts have pointed to the tight regulation of the TIA pathway and to multiple rate-limiting reactions. Transcriptional regulator ORCA3 (octadecanoid responsive Catharanthus AP2-domain protein), activated by jasmonic acid, plays a central role in regulating the TIA pathway. In this study, overexpressing ORCA3 under the control of a glucocorticoid-inducible promoter in C. roseus hairy roots resulted in no change in the total amount of TIAs measured. RT-qPCR results showed that ORCA3 overexpression triggered the upregulation of transcripts of most of the known TIA pathway genes. One notable exception was the decrease in strictosidine glucosidase (SGD) transcripts. These results corresponded to previously published results. In this study, ORCA3 and SGD were both engineered in hairy roots under the control of a glucocorticoid-inducible promoter. Co-overexpression of ORCA3 and SGD resulted in a significant (p < 0.05) increase in serpentine by 44 %, ajmalicine by 32 %, catharanthine by 38 %, tabersonine by 40 %, lochnericine by 60 % and hörhammericine by 56 % . The total alkaloid pool was increased significantly by 47 %. Thus, combining overexpression of a positive regulator and a pathway gene which is not controlled by this regulator provided a way to enhance alkaloid production.

The bHLH transcription factor BIS1 controls the iridoid branch of the monoterpenoid indole alkaloid pathway in Catharanthus roseus

Plants make specialized bioactive metabolites to defend themselves against attackers. The conserved control mechanisms are based on transcriptional activation of the respective plant species-specific biosynthetic pathways by the phytohormone jasmonate. Knowledge of the transcription factors involved, particularly in terpenoid biosynthesis, remains fragmentary. By transcriptome analysis and functional screens in the medicinal plant Catharanthus roseus (Madagascar periwinkle), the unique source of the monoterpenoid indole alkaloid (MIA)-type anticancer drugs vincristine and vinblastine, we identified a jasmonate-regulated basic helix-loop-helix (bHLH) transcription factor from clade IVa inducing the monoterpenoid branch of the MIA pathway. The bHLH iridoid synthesis 1 (BIS1) transcription factor transactivated the expression of all of the genes encoding the enzymes that catalyze the sequential conversion of the ubiquitous terpenoid precursor geranyl diphosphate to the iridoid loganic acid. BIS1 acted in a complementary manner to the previously characterized ethylene response factor Octadecanoid derivative-Responsive Catharanthus APETALA2-domain 3 (ORCA3) that transactivates the expression of several genes encoding the enzymes catalyzing the conversion of loganic acid to the downstream MIAs. In contrast to ORCA3, overexpression of BIS1 was sufficient to boost production of high-value iridoids and MIAs in C. roseus suspension cell cultures. Hence, BIS1 might be a metabolic engineering tool to produce sustainably high-value MIAs in C. roseus plants or cultures.

De novo transcriptome sequencing and digital gene expression analysis predict biosynthetic pathway of rhynchophylline and isorhynchophylline from Uncaria rhynchophylla, a non-model plant with potent anti-alzheimer's properties

Background

The major medicinal alkaloids isolated from Uncaria rhynchophylla (gouteng in chinese) capsules are rhynchophylline (RIN) and isorhynchophylline (IRN). Extracts containing these terpene indole alkaloids (TIAs) can inhibit the formation and destabilize preformed fibrils of amyloid β protein (a pathological marker of Alzheimer’s disease), and have been shown to improve the cognitive function of mice with Alzheimer-like symptoms. The biosynthetic pathways of RIN and IRN are largely unknown.

Results

In this study, RNA-sequencing of pooled Uncaria capsules RNA samples taken at three developmental stages that accumulate different amount of RIN and IRN was performed. More than 50 million high-quality reads from a cDNA library were generated and de novo assembled. Sequences for all of the known enzymes involved in TIAs synthesis were identified. Additionally, 193 cytochrome P450 (CYP450), 280 methyltransferase and 144 isomerase genes were identified, that are potential candidates for enzymes involved in RIN and IRN synthesis. Digital gene expression profile (DGE) analysis was performed on the three capsule developmental stages, and based on genes possessing expression profiles consistent with RIN and IRN levels; four CYP450s, three methyltransferases and three isomerases were identified as the candidates most likely to be involved in the later steps of RIN and IRN biosynthesis.

Conclusion

A combination of de novo transcriptome assembly and DGE analysis was shown to be a powerful method for identifying genes encoding enzymes potentially involved in the biosynthesis of important secondary metabolites in a non-model plant. The transcriptome data from this study provides an important resource for understanding the formation of major bioactive constituents in the capsule extract from Uncaria, and provides information that may aid in metabolic engineering to increase yields of these important alkaloids.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-676) contains supplementary material, which is available to authorized users.

Analyses of Catharanthus roseus and Arabidopsis thaliana WRKY transcription factors reveal involvement in jasmonate signaling

BACKGROUND

To combat infection to biotic stress plants elicit the biosynthesis of numerous natural products, many of which are valuable pharmaceutical compounds. Jasmonate is a central regulator of defense response to pathogens and accumulation of specialized metabolites. Catharanthus roseus produces a large number of terpenoid indole alkaloids (TIAs) and is an excellent model for understanding the regulation of this class of valuable compounds. Recent work illustrates a possible role for the Catharanthus WRKY transcription factors (TFs) in regulating TIA biosynthesis. In Arabidopsis and other plants, the WRKY TF family is also shown to play important role in controlling tolerance to biotic and abiotic stresses, as well as secondary metabolism.

RESULTS

Here, we describe the WRKY TF families in response to jasmonate in Arabidopsis and Catharanthus. Publically available Arabidopsis microarrays revealed at least 30% (22 of 72) of WRKY TFs respond to jasmonate treatments. Microarray analysis identified at least six jasmonate responsive Arabidopsis WRKY genes (AtWRKY7, AtWRKY20, AtWRKY26, AtWRKY45, AtWRKY48, and AtWRKY72) that have not been previously reported. The Catharanthus WRKY TF family is comprised of at least 48 members. Phylogenetic clustering reveals 11 group I, 32 group II, and 5 group III WRKY TFs. Furthermore, we found that at least 25% (12 of 48) were jasmonate responsive, and 75% (9 of 12) of the jasmonate responsive CrWRKYs are orthologs of AtWRKYs known to be regulated by jasmonate.

CONCLUSION

Overall, the CrWRKY family, ascertained from transcriptome sequences, contains approximately 75% of the number of WRKYs found in other sequenced asterid species (pepper, tomato, potato, and bladderwort). Microarray and transcriptomic data indicate that expression of WRKY TFs in Arabidopsis and Catharanthus are under tight spatio-temporal and developmental control, and potentially have a significant role in jasmonate signaling. Profiling of CrWRKY expression in response to jasmonate treatment revealed potential associations with secondary metabolism. This study provides a foundation for further characterization of WRKY TFs in jasmonate responses and regulation of natural product biosynthesis.

Promoter analysis reveals cis-regulatory motifs associated with the expression of the WRKY transcription factor CrWRKY1 in Catharanthus roseus

WRKY transcription factors (TFs) are emerging as an important group of regulators of plant secondary metabolism. However, the cis-regulatory elements associated with their regulation have not been well characterized. We have previously demonstrated that CrWRKY1, a member of subgroup III of the WRKY TF family, regulates biosynthesis of terpenoid indole alkaloids in the ornamental and medicinal plant, Catharanthus roseus. Here, we report the isolation and functional characterization of the CrWRKY1 promoter. In silico analysis of the promoter sequence reveals the presence of several potential TF binding motifs, indicating the involvement of additional TFs in the regulation of the TIA pathway. The CrWRKY1 promoter can drive the expression of a β-glucuronidase (GUS) reporter gene in native (C. roseus protoplasts and transgenic hairy roots) and heterologous (transgenic tobacco seedlings) systems. Analysis of 5'- or 3'-end deletions indicates that the sequence located between positions -140 to -93 bp and -3 to +113 bp, relative to the transcription start site, is critical for promoter activity. Mutation analysis shows that two overlapping as-1 elements and a CT-rich motif contribute significantly to promoter activity. The CrWRKY1 promoter is induced in response to methyl jasmonate (MJ) treatment and the promoter region between -230 and -93 bp contains a putative MJ-responsive element. The CrWRKY1 promoter can potentially be used as a tool to isolate novel TFs involved in the regulation of the TIA pathway.

Transcriptional regulation of secondary metabolite biosynthesis in plants

Plants produce thousands of secondary metabolites (a.k.a. specialized metabolites) of diverse chemical nature. These compounds play important roles in protecting plants under adverse conditions. Many secondary metabolites are valued for their pharmaceutical properties. Because of their beneficial effects to health, biosynthesis of secondary metabolites has been a prime focus of research. Many transcription factors have been characterized for their roles in regulating biosynthetic pathways at the transcriptional level. The emerging picture of transcriptional regulation of secondary metabolite biosynthesis suggests that the expression of activators and repressors, in response to phytohormones and different environmental signals, forms a dynamic regulatory network that fine-tune the timing, amplitude and tissue specific expression of pathway genes and the subsequent accumulation of these compounds. Recent research has revealed that some metabolic pathways are also controlled by posttranscriptional and posttranslational mechanisms. This review will use recent developments in the biosynthesis of flavonoids, alkaloids and terpenoids to highlight the complexity of transcriptional regulation of secondary metabolite biosynthesis.

Overexpression of ORCA3 and G10H in Catharanthus roseus plants regulated alkaloid biosynthesis and metabolism revealed by NMR-metabolomics

In order to improve the production of the anticancer dimeric indole alkaloids in Catharanthuse roseus, much research has been dedicated to culturing cell lines, hairy roots, and efforts to elucidate the regulation of the monoterpenoid indole alkaloid (MIA) biosynthesis. In this study, the ORCA3 (Octadecanoid-derivative Responsive Catharanthus AP2-domain) gene alone or integrated with the G10H (geraniol 10-hydroxylase) gene were first introduced into C. roseus plants. Transgenic C. roseus plants overexpressing ORCA3 alone (OR lines), or co-overexpressing G10H and ORCA3 (GO lines) were obtained by genetic modification. ORCA3 overexpression induced an increase of AS, TDC, STR and D4H transcripts but did not affect CRMYC2 and G10H transcription. G10H transcripts showed a significant increase under G10H and ORCA3 co-overexpression. ORCA3 and G10H overexpression significantly increased the accumulation of strictosidine, vindoline, catharanthine and ajmalicine but had limited effects on anhydrovinblastine and vinblastine levels. NMR-based metabolomics confirmed the higher accumulation of monomeric indole alkaloids in OR and GO lines. Multivariate data analysis of (1)H NMR spectra showed change of amino acid, organic acid, sugar and phenylpropanoid levels in both OR and GO lines compared to the controls. The result indicated that enhancement of MIA biosynthesis by ORCA3 and G10H overexpression might affect other metabolic pathways in the plant metabolism of C. roseus.

Molecular cloning and functional characterization of Catharanthus roseus hydroxymethylbutenyl 4-diphosphate synthase gene promoter from the methyl erythritol phosphate pathway

The Madagascar periwinkle produces monoterpenoid indole alkaloids (MIA) of high interest due to their therapeutical values. The terpenoid moiety of MIA is derived from the methyl erythritol phosphate (MEP) and seco-iridoid pathways. These pathways are regarded as the limiting branch for MIA biosynthesis in C. roseus cell and tissue cultures. In previous studies, we demonstrated a coordinated regulation at the transcriptional and spatial levels of genes from both pathways. We report here on the isolation of the 5'-flanking region (1,049 bp) of the hydroxymethylbutenyl 4-diphosphate synthase (HDS) gene from the MEP pathway. To investigate promoter transcriptional activities, the HDS promoter was fused to GUS reporter gene. Agrobacterium-mediated transformation of young tobacco leaves revealed that the cloned HDS promoter displays a tissue-specific GUS staining restricted to the vascular region of the leaves and limited to a part of the vein that encompasses the phloem in agreement with the previous localization of HDS transcripts in C. roseus aerial organs. Further functional characterizations in stably or transiently transformed C. roseus cells allowed us to identify the region that can be consider as the minimal promoter and to demonstrate the induction of HDS promoter by several hormonal signals (auxin, cytokinin, methyljasmonate and ethylene) leading to MIA production. These results, and the bioinformatic analysis of the HDS 5'-region, suggest that the HDS promoter harbours a number of cis-elements binding specific transcription factors that would regulate the flux of terpenoid precursors involved in MIA biosynthesis.

The transcription factor CrWRKY1 positively regulates the terpenoid indole alkaloid biosynthesis in Catharanthus roseus

Catharanthus roseus produces a large array of terpenoid indole alkaloids (TIAs) that are an important source of natural or semisynthetic anticancer drugs. The biosynthesis of TIAs is tissue specific and induced by certain phytohormones and fungal elicitors, indicating the involvement of a complex transcriptional control network. However, the transcriptional regulation of the TIA pathway is poorly understood. Here, we describe a C. roseus WRKY transcription factor, CrWRKY1, that is preferentially expressed in roots and induced by the phytohormones jasmonate, gibberellic acid, and ethylene. The overexpression of CrWRKY1 in C. roseus hairy roots up-regulated several key TIA pathway genes, especially Tryptophan Decarboxylase (TDC), as well as the transcriptional repressors ZCT1 (for zinc-finger C. roseus transcription factor 1), ZCT2, and ZCT3. However, CrWRKY1 overexpression repressed the transcriptional activators ORCA2, ORCA3, and CrMYC2. Overexpression of a dominant-repressive form of CrWRKY1, created by fusing the SRDX repressor domain to CrWRKY1, resulted in the down-regulation of TDC and ZCTs but the up-regulation of ORCA3 and CrMYC2. CrWRKY1 bound to the W box elements of the TDC promoter in electrophoretic mobility shift, yeast one-hybrid, and C. roseus protoplast assays. Up-regulation of TDC increased TDC activity, tryptamine concentration, and resistance to 4-methyl tryptophan inhibition of CrWRKY1 hairy roots. Compared with control roots, CrWRKY1 hairy roots accumulated up to 3-fold higher levels of serpentine. The preferential expression of CrWRKY1 in roots and its interaction with transcription factors including ORCA3, CrMYC2, and ZCTs may play a key role in determining the root-specific accumulation of serpentine in C. roseus plants.

Natural Products Genomics: A novel approach for the discovery of anti-cancer therapeutics

Plants continue to retain some advantages over combinatorial chemistry as sources of novel compounds, for example, they can generate metabolites with a complexity beyond synthetic chemistry. However, this comes with its own problems in production and synthetic modification of these compounds. Natural Products Genomics (NPG) aims to access the plants own genomic capacity to increase yields, and modify complex bioactive metabolites, to alleviate these limitations. NPG uses a combination of gain of function mutagenesis and selection to a) mimic the evolution of novel compounds in plants, and b) to increase yields of known bioactive metabolites. This process is performed rapidly at the cell culture level in large populations of mutants. Two examples demonstrating proof of concept in Nicotiana tabacum (tobacco) and proof of application in the medicinal plant species Catharanthus roseus, are included to illustrate the feasibility of this approach. This biotechnology platform may alter the way in which plant drug discovery is perceived by the pharmaceutical industry, and provides an alternative to combinatorial chemistry for the discovery, modification and production of highly complex bioactive molecules.

Flavonoid-related basic helix-loop-helix regulators, NtAn1a and NtAn1b, of tobacco have originated from two ancestors and are functionally active

The basic helix-loop-helix (bHLH) transcription factors (TFs) comprise one of the largest families of TFs involved in developmental and physiological processes in plants. Here, we describe the functional characterization of two bHLH TFs (NtAn1a and NtAn1b) isolated from tobacco (Nicotiana tabacum) flowers. NtAn1a and NtAn1b originate from two ancestors of tobacco, N. sylvestris and N. tomentosiformis, respectively. NtAn1a and NtAn1b share high sequence similarity with other known flavonoid-related bHLH TFs and are predominantly expressed in flowers. GUS expression driven by the NtAn1a promoter is consistent with NtAn1 transcript profile in tobacco flowers. Both NtAn1a and NtAn1b are transcriptional activators as demonstrated by transactivation assays using yeast cells and tobacco protoplasts. Ectopic expression of NtAn1a or NtAn1b enhances anthocyanin accumulation in tobacco flowers. In transgenic tobacco expressing NtAn1a or NtAn1b, both subsets of early and late flavonoid pathway genes were up-regulated. Yeast two-hybrid assays showed that NtAn1 proteins interact with the previously characterized R2R3-MYB TF, NtAn2. The NtAn1-NtAn2 complex activated the promoters of two key anthocyanin pathway genes, dihydroflavonol reductase and chalcone synthase. The promoter activation is severely repressed by dominant repressive forms of either NtAn1a or NtAn2, created by fusing the SRDX repressor domain to the TFs. Our results show that NtAn1 and NtAn2 act in concert to regulate the anthocyanin pathway in tobacco flowers and NtAn2 up-regulates NtAn1 gene expression.

Functional analysis of the DAT gene promoter using transient Catharanthus roseus and stable Nicotiana tabacum transformation systems

The Catharanthus roseus DAT gene encodes the enzyme acetyl-CoA:deacetylvindoline-4-O-acetyltransferase involved in the last step of the indole alkaloid pathway leading to vindoline. This gene is characterized by specific cell type expression in idioblasts and laticifers. To understand the specific transcriptional regulation mechanism(s) of DAT, several DAT promoter GUS constructs were cloned into pCAMBIA1305.1. Agroinfiltration of different explant types of C. roseus resulted in organ-specific accumulation of GUS, albeit at various levels. Heterologous accumulation of GUS in transgenic tobacco revealed both general and non-specific expression with the exception of a stomata-specific expression when 2.3 kb of the DAT promoter was coupled with a portion of the DAT ORF. These results suggest that in addition to the 2.3 kb upstream of the DAT transcriptional start site, additional cis-acting elements may be responsible for the specific spatial expression of DAT in vivo. Furthermore, hairy roots transformed with DAT promoter GUS constructs demonstrated GUS expression in root tissues (visualized through GUS enzyme activity), even though DAT is repressed in non-transformed roots.

Functional expression of geraniol 10-hydroxylase reveals its dual function in the biosynthesis of terpenoid and phenylpropanoid

Geraniol 10-hydroxylase (G10H), a cytochrome P450 monooxygenase, has been reported to be involved in the biosynthesis of terpenoid indole alkaloids. The gene for Catharanthus roseus G10H (CrG10H) was cloned and heterologously expressed in baculovirus-infected insect cells. A number of substrates were subjected to assay the enzyme activity of CrG10H. As reported in a previous study, CrG10H hydroxylated the monoterpenoid geraniol at the C-10 position to generate 10-hydroxygeraniol. Interestingly, CrG10H also catalyzed 3'-hydroxylation of naringenin to produce eriodictyol. Coexpression of an Arabidopsis NADPH P450 reductase substantially increased the ability of CrG10H to hydroxylate naringenin. The catalytic activity of CrG10H was approximately 10 times more efficient with geraniol than with naringenin, judged by the k(cat)/K(m) values. Thus, G10H also plays an important role in the biosynthetic pathway of flavonoids, in addition to its previously described role in the metabolism of terpenoids.

Overexpression of an apoplastic peroxidase gene CrPrx in transgenic hairy root lines of Catharanthus roseus

Peroxidases are a family of isoenzymes found in all higher plants and are known to be involved in a broad range of physiological processes. However, very little information is available concerning their role in Catharanthus roseus. The present study describes the impact of both overexpression and suppression of a peroxidase gene, CrPrx in C. roseus transgenic hairy root lines. Real-time PCR analysis in 35S-CrPrx and CrPrx-RNAi transgenic lines indicated differential transcript profile for peroxidases as well as for genes and regulators involved in MIA (monoterpenoid indole alkaloid) pathway of C. roseus. Comparative analysis revealed that MIA pathway genes showing elevated levels of expression in 35S-CrPrx transgenic lines showed a significant reduction in their transcript level in CrPrx-RNAi transgenic lines. Metabolite analysis detected higher levels of ajmalicine and serpentine accumulation in overexpressed lines. It was observed that all overexpressed transgenic lines produced more amount of H(2)O(2). These results indicate a role of CrPrx gene in the regulation of MIA pathway genes and regulators, thus affecting the production of specific alkaloids.

Functional analysis of Gossypium hirsutum cellulose synthase catalytic subunit 4 promoter in transgenic Arabidopsis and cotton tissues

Gossypium hirsutum cellulose synthase catalytic subunit 4 (GhCesA4) plays an important role in cellulose biosynthesis during cotton fiber development. The transcript levels of GhCesA4 are significantly up-regulated as secondary cell wall cellulose is produced in developing cotton fibers. To understand the molecular mechanisms involved in transcriptional regulation of GhCesA4, β-glucuronidase (GUS) activity regulated by a GhCesA4 promoter (-2574/+56) or progressively deleted promoters were determined in both cotton tissues and transgenic Arabidopsis. The spatial regulation of GhCesA4 expression was similar between cotton tissues and transgenic Arabidopsis. GUS activity regulated by the GhCesA4 promoter (-2574/+56) was found in trichomes and root vascular tissues in both cotton and transgenic Arabidopsis. The -2574/-1824 region was responsible for up-regulation of GhCesA4 expression in trichomes and root vascular tissues in transgenic Arabidopsis. The -1824/-1355 region negatively regulated GhCesA4 expression in most Arabidopsis vascular tissues. For vascular expression in stems and leaves, the -898/-693 region was required. The -693/-320 region of the GhCesA4 promoter was necessary for basal expression of GhCesA4 in cotton roots as well as Arabidopsis roots. Exogenous phytohormonal treatments on transgenic Arabidopsis revealed that phytohormones may be involved in the differential regulation of GhCesA4 during cotton fiber development.

The expression of 1-deoxy-D-xylulose synthase and geraniol-10-hydroxylase or anthranilate synthase increases terpenoid indole alkaloid accumulation in Catharanthus roseus hairy roots

The terpenoid indole alkaloid (TIA) pathway in Catharanthus roseus produces two important anticancer drugs, vinblastine and vincristine, in very low yields. This study focuses on overexpressing several key genes in the upper part of the TIA pathway in order to increase flux toward downstream metabolites within hairy root cultures. Specifically, we constructed hairy root lines with inducible overexpression of 1-deoxy-D-xylulose synthase (DXS) or geraniol-10-hydroxylase (G10H). We also constructed hairy root lines with inducible expression of DXS and anthranilate synthase α subunit (ASA) or DXS and G10H. DXS overexpression resulted in a significant increase in ajmalicine by 67%, serpentine by 26% and lochnericine by 49% and a significant decrease in tabersonine by 66% and hörhammericine by 54%. Co-overexpression of DXS and G10H caused a significant increase in ajmalicine by 16%, lochnericine by 31% and tabersonine by 13%. Likewise, DXS and ASA overexpression displayed a significant increase in hörhammericine by 30%, lochnericine by 27% and tabersonine by 34%. These results point to the need for overexpressing multiple genes within the pathway to increase the flux toward vinblastine and vincristine.

Transcriptional response of the catharanthine biosynthesis pathway to methyl jasmonate/nitric oxide elicitation in Catharanthus roseus hairy root culture

Jasmonates and nitric oxide (NO) play important roles in the regulation of the signaling network leading to the biosynthesis of plant secondary metabolites. In this work, we explore the effect of constitutive overexpression of CrORCA3 (octadecanoid-responsive Catharanthus AP2/ERF domain), methyl jasmonate (MeJA), and sodium nitroprusside (SNP) on the differentiated tissue of Catharanthus roseus hairy roots. The changes in catharanthine concentration and in the levels of mRNA transcripts of pathway genes and regulators were tracked for 192 h. ORCA3 overexpression led to a slight decrease of the accumulation of catharanthine, while MeJA treatment caused a large increase in the levels of transcripts of pathway genes and the catharanthine concentration. SNP treatment alone or SNP in combination with MeJA treatment caused a dramatic decrease of the cathanranthine concentration, while at the same time the levels of transcripts of zinc finger-binding proteins genes (ZCTs) increased. The latter treatment also caused a decrease of the levels of transcripts of type-I protein prenyltransferase gene (PGGT-I). This response of transcriptional repressors and pathway genes may explain the antagonistic effects of NO and MeJA on catharanthine biosynthesis in C. roseus hairy roots.

Overexpression of G10H and ORCA3 in the hairy roots of Catharanthus roseus improves catharanthine production

A number of genes that function in the terpenoid indole alkaloids (TIAs) biosynthesis pathway have been identified in Catharanthus roseus. Except for the geraniol 10-hydroxylase (G10H) gene, which encodes a cytochrome P450 monooxygenase, several of these genes are up-regulated by ORCA3, a jasmonate-responsive APETALA2 (AP2)-domain transcript factor. In this study, the G10H gene was transformed independently, or co-transformed with ORCA3 into C. roseus, using Agrobacterium rhizogenes MSU440. Hairy root clones expressing the G10H gene alone, or both the G10H and ORCA3 genes, were obtained. Alkaloid accumulation level analyses showed that all transgenic clones accumulated more catharanthine, with the highest accumulation level in the transgenic clone OG12 (6.5-fold higher than that of the non-expression clone). Following treatment with ABA, accumulation of catharanthine reached 1.96 mg/g DW in the transgenic clone OG12. The expression levels of TIAs biosynthesis genes in transgenic and non-transgenic clones were also investigated.

Isolation and functional characterization of a floral tissue-specific R2R3 MYB regulator from tobacco

Tobacco is a commonly used heterologous system for studying combinatorial regulation of the flavonoid biosynthetic pathway by the bHLH-MYB transcription factor (TF) complex in plants. However, little is known about the endogenous tobacco bHLH and MYB TFs involved in the pathway. Ectopic expression in tobacco of heterologous bHLH TF genes, such as maize Lc, leads to increased anthocyanin production in the reproductive tissues, suggesting the presence of a reproductive tissue-specific MYB TF that interacts with the Lc-like bHLH TFs. We isolated a gene (NtAn2) encoding a R2R3 MYB TF from developing tobacco flowers. NtAn2 shares high sequence homology with other known flavonoid-related MYB TFs and is mostly expressed in developing flowers. Constitutive ectopic expression of NtAn2 induces whole-plant anthocyanin production in tobacco and Arabidopsis. In transgenic tobacco and Arabidopsis expressing NtAn2, both subsets of early and late flavonoid pathway genes are up-regulated. Suppression of NtAn2 by RNAi in tobacco resulted in a white-flowered phenotype and the inhibition of the late pathway genes. Yeast two-hybrid assays demonstrated that NtAn2 can interact with five heterologous bHLH TFs known to induce anthocyanin synthesis in other species including maize, perilla, snapdragon and Arabidopsis. Bimolecular fluorescent complementation using split YFP demonstrated that NtAn2 interacts with Lc in tobacco cells and that the complex is localized to nuclei. Transient co-expression of NtAn2 and Lc or Arabidopsis TT8 in tobacco protoplasts activated the promoters of two key flavonoid pathway genes, chalcone synthase and dihydroflavonol reductase. These results suggest that NtAn2 is a key gene controlling anthocyanin production in reproductive tissues of tobacco.

Isolation and functional analysis of the Catharanthus roseus deacetylvindoline-4-O-acetyltransferase gene promoter

Madagascar periwinkle (Catharanthus roseus) produces many therapeutically valuable terpenoid indole alkaloids (TIAs), such as vinblastine and vincristine derived from the monomers vindoline and catharanthine. Deacetylvindoline-4-O-acetyltransferase (DAT) is a key enzyme for the terminal step of vindoline biosynthesis. In this research, the DAT gene promoter was cloned, sequenced, and analyzed. An approximately 1,773 bp genomic DNA fragment of DAT promoter was obtained. Sequence analysis revealed that DAT promoter contained several potential regulatory elements which were involved in the regulation of gene expression. To investigate its function, the promoter fragments with 5' deletions and gain-of-function deletions were fused to GUS reporter gene, and their expressions were analyzed by transient expression in C. roseus cell suspensions. The regulatory activity of DAT promoter was identified with fluorescence quantitative assays. Three TGACG motifs and one inverted motif (CGTCA) between -808 and -1,086 bp in the DAT promoter were found to be involved in methyljasmonate signal transduction pathway.