Metabolic engineering of Nicotiana benthamiana for the increased production of taxadiene

We report the production of taxadiene by transformation of N. benthamiana with a taxadiene synthase gene. The production was significantly increased by an elicitor treatment or metabolic pathway shunting. Paclitaxel (Taxol(®)) was first isolated from the bark of the pacific yew tree as an anticancer agent and has been used extensively to treat various types of cancer. Taxadiene, the first committed product of paclitaxel synthesis is cyclized from geranylgeranyl diphosphate (GGPP), and further complex hydroxylation and acylation processes of the unique taxane core skeleton produce paclitaxel. To accomplish de novo production of taxadiene, we transformed Nicotiana benthamiana with a taxadiene synthase (TS) gene. The introduced TS gene under the transcriptional control of the CaMV 35S promoter was constitutively expressed in N. benthamiana, and the de novo production of taxadiene was confirmed by mass spectroscopy profiling. Transformed N. benthamiana homozygous lines produced 11-27 μg taxadiene/g of dry weight. The highest taxadiene production line TSS-8 was further treated with an elicitor, methyl jasmonate, and metabolic pathway shunting by suppression of the phytoene synthase gene expression which resulted in accumulation of increased taxadiene accumulation by 1.4- or 1.9-fold, respectively. In summary, we report that the production of taxadiene in N. benthamiana was possible by the ectopic expression of the TS gene, and higher accumulation of taxadiene could be achieved by elicitor treatment or metabolic pathway shunting of the terpenoid pathway.

Taxol biosynthesis: tyrocidine synthetase A catalyzes the production of phenylisoserinyl CoA and other amino phenylpropanoyl thioesters

In Taxus plants the biosynthesis of the pharmaceutical paclitaxel includes the transfer of β-amino phenylpropanoyls from coenzyme A to the diterpenoid baccatin III by an acyl CoA-dependent acyltransferase. Several enzymes on the pathway are known, yet a few remain unidentified, including the putative ligase that biosynthesizes key β-amino phenylpropanoyl CoAs. The multienzyme, nonribosomal peptide synthetase that produces tyrocidines contains a tridomain starter module tyrocidine synthetase A that normally activates (S)-α-Phe to an adenylate anhydride in the adenylation domain. The Phe moiety is then thioesterified by the pendent pantetheine of the adjacent thiolation domain. Herein, the adenylation domain was found to function as a CoA ligase, making α-, β-phenylalanyl, and phenylisoserinyl CoA. The latter two are substrates of a phenylpropanoyltransferase on the biosynthetic pathway of the antimitotic paclitaxel.

[Advances of taxol combinatorial biosynthesis]

Taxol is a kind of isoprenoid with strong anticancer activity. It is difficult to be obtained because of its low concentration in nature, which hinders its application in cancer treatment. Recently, biosynthesis methods for taxol production have attracted more attentions. Several systems including Escherichia coli, Saccharomyces cerevisiae, Physcomitrella patens, Arabidopsis, tomato and ginseng were explored. This review focuses on the advance in biosynthesis of taxol in different systems and features the bottleneck of scale fermentation for producing the intermediates. At the same time some advices for the further were given. At last, the future and character of Physcomitrella patens system used in taxol combinatorial biosynthesis were analyzed based on our lab's research.

[Application and prospect of fungi elicitors in fermentation industry]

Fungal elicitors are a group of chemicals that can stimulate the secondary metabolite production in plants and microbial cells. After being recognized, it could enhance the expression of related genes through the signal-transduction pathway; regulate the activity of the enzyme involved in the biosynthesis of secondary metabolites. In recent years, the inducible mechanism of fungal elicitors has been studied deeply worldwide. Meanwhile, it has acquired wide concern in the area of biological industry, especially in the fermentation industry. This paper addresses the application and prospect of fungal elicitors in the secondary metabolites of plant and microbial cells.

A fungal endophyte induces transcription of genes encoding a redundant fungicide pathway in its host plant

BACKGROUND

Taxol is an anti-cancer drug harvested from Taxus trees, proposed ecologically to act as a fungicide. Taxus is host to fungal endophytes, defined as organisms that inhabit plants without causing disease. The Taxus endophytes have been shown to synthesize Taxol in vitro, providing Taxus with a second potential biosynthetic route for this protective metabolite. Taxol levels in plants vary 125-fold between individual trees, but the underlying reason has remained unknown.

RESULTS

Comparing Taxus trees or branches within a tree, correlations were observed between Taxol content, and quantity of its resident Taxol-producing endophyte, Paraconiothyrium SSM001. Depletion of fungal endophyte in planta by fungicide reduced plant Taxol accumulation. Fungicide treatment of intact plants caused concomitant decreases in transcript and/or protein levels corresponding to two critical genes required for plant Taxol biosynthesis. Taxol showed fungicidal activity against fungal pathogens of conifer wood, the natural habitat of the Taxol-producing endophyte. Consistent with other Taxol-producing endophytes, SSM001 was resistant to Taxol.

CONCLUSIONS

These results suggest that the variation in Taxol content between intact Taxus plants and/or tissues is at least in part caused by varying degrees of transcriptional elicitation of plant Taxol biosynthetic genes by its Taxol-producing endophyte. As Taxol is a fungicide, and the endophyte is resistant to Taxol, we discuss how this endophyte strategy may be to prevent colonization by its fungal competitors but at minimal metabolic cost to itself.

Deep sequencing reveals transcriptome re-programming of Taxus × media cells to the elicitation with methyl jasmonate

Background

Plant cell culture represents an alternative source for producing high-value secondary metabolites including paclitaxel (Taxol®), which is mainly produced in Taxus and has been widely used in cancer chemotherapy. The phytohormone methyl jasmonate (MeJA) can significantly increase the production of paclitaxel, which is induced in plants as a secondary metabolite possibly in defense against herbivores and pathogens. In cell culture, MeJA also elicits the accumulation of paclitaxel; however, the mechanism is still largely unknown.

Methodology/Principal Findings

To obtain insight into the global regulation mechanism of MeJA in the steady state of paclitaxel production (7 days after MeJA addition), especially on paclitaxel biosynthesis, we sequenced the transcriptomes of MeJA-treated and untreated Taxus × media cells and obtained ∼ 32.5 M high quality reads, from which 40,348 unique sequences were obtained by de novo assembly. Expression level analysis indicated that a large number of genes were associated with transcriptional regulation, DNA and histone modification, and MeJA signaling network. All the 29 known genes involved in the biosynthesis of terpenoid backbone and paclitaxel were found with 18 genes showing increased transcript abundance following elicitation of MeJA. The significantly up-regulated changes of 9 genes in paclitaxel biosynthesis were validated by qRT-PCR assays. According to the expression changes and the previously proposed enzyme functions, multiple candidates for the unknown steps in paclitaxel biosynthesis were identified. We also found some genes putatively involved in the transport and degradation of paclitaxel. Potential target prediction of miRNAs indicated that miRNAs may play an important role in the gene expression regulation following the elicitation of MeJA.

Conclusions/Significance

Our results shed new light on the global regulation mechanism by which MeJA regulates the physiology of Taxus cells and is helpful to understand how MeJA elicits other plant species besides Taxus.

[The advance in synthetic biology: towards a microbe-derived paclitaxel intermediates]

The synthetic biology matures to promote the heterologous biosynthesis of the well-known drug paclitaxel that is one of the most important and active chemotherapeutic agents for the first-line clinical treatment of cancer. This review focuses on the construction and regulation of the biosynthetic pathway of paclitaxel intermediates in both Escherichia coli and Saccharomyces cerevisiae. In particular, the review also features the early efforts to design and overproduce taxadiene and the bottleneck of scale fermentation for producing the intermediates.

Bioprocessing of plant in vitro systems for the mass production of pharmaceutically important metabolites: paclitaxel and its derivatives

Taxol (paclitaxel) and its derivatives are microtubule-stabilizing drugs widely used in the treatment of several types of cancer, including mammary, prostate, ovarian and non-small-cell lung carcinoma, as well as AIDS-associated Kaposi's sarcoma and other types of tumor. Taxanes stabilize microtubules by enhancing their polymerization and inhibiting depolymerization. Microtubule dynamics are crucial to mitotic spindle formation and function; therefore, cells exposed to taxanes are unable to undergo chromosomal separation during mitosis, become arrested in the G2/M phases of the cell cycle, and are subsequently targeted for apoptosis. Plant cell cultures are used for industrial-scale biotechnological production of important bioactive plant secondary metabolites, including the anticancer agent paclitaxel. In the last two decades, there have been numerous empirical approaches to improve the biotechnological production of taxanes, leading to the conclusion that treatment of Taxus sp. cells with methyl jasmonate or other elicitors is the most effective strategy. However, little insight has been gained into how the elicitors increase taxane biosynthesis or how this process is regulated. In recent years, with the help of "omics" tools, a rational approach has provided new information about taxane metabolism and its control. Once pathway bottlenecks have been identified, it will be possible to engineer Taxus sp. cell lines with overexpression of genes that control the flux-limiting steps, thus boosting taxane productivity. This review describes the chemical and biological characterization of paclitaxel and its derivatives and discusses future prospects for their biotechnological production.

[Research progress and trend analysis of biology and chemistry of Taxus medicinal resources]

Taxus is the source plant of anti-cancer drug paclitaxel and its biosynthetic precursor, analogs and derivatives, which has been studying for decades. There are many endemic Taxus species in China, which have been studied in the field of multiple disciplines. Based on the recent studies of the researchers, this review comments on the study of Taxus biology and chemistry. The bibliometric method is used to quantify the global scientific production of Taxus-related research, and identify patterns and tendencies of Taxus-related articles. Gaps are present in knowledge about the genomics, epigenomics, transcriptomics, proteomics, metabolomics and bioinformatics of Taxus and their endophytic fungi. Systems biology and various omics technologies will play an increasingly important role in the coming decades.

Assessment of genetic and epigenetic variation during long-term Taxus cell culture

Gradual loss of secondary metabolite production is a common obstacle in the development of a large-scale plant cell production system. In this study, cell morphology, paclitaxel (Taxol®) biosynthetic ability, and genetic and epigenetic variations in the long-term culture of Taxus media cv Hicksii cells were assessed over a 5-year period to evaluate the mechanisms of the loss of secondary metabolites biosynthesis capacity in Taxus cell. The results revealed that morphological variations, gradual loss of paclitaxel yield and decreased transcriptional level of paclitaxel biosynthesis key genes occurred during long-term subculture. Genetic and epigenetic variations in these cultures were also studied at different times during culture using amplified fragment-length polymorphism (AFLP), methylation-sensitive amplified polymorphism (MSAP), and high-performance liquid chromatography (HPLC) analyses. A total of 32 primer combinations were used in AFLP amplification, and none of the AFLP loci were found to be polymorphic, thus no major genetic rearrangements were detected in any of the tested samples. However, results from both MSAP and HPLC indicated that there was a higher level of DNA methylation in the low-paclitaxel yielding cell line after long-term culture. Based on these results, we proposed that accumulation of paclitaxel in Taxus cell cultures might be regulated by DNA methylation. To our knowledge, this is the first report of increased methylation with the prolongation of culture time in Taxus cell culture. It provides substantial clues for exploring the gradual loss of the taxol biosynthesis capacity of Taxus cell lines during long-term subculture.

KEY MESSAGE

DNA methylation maybe involved in the regulation of paclitaxel biosynthesis in Taxus cell culture.

Recent advances towards development and commercialization of plant cell culture processes for the synthesis of biomolecules

Plant cell culture systems were initially explored for use in commercial synthesis of several high-value secondary metabolites, allowing for sustainable production that was not limited by the low yields associated with natural harvest or the high cost associated with complex chemical synthesis. Although there have been some commercial successes, most notably paclitaxel production from Taxus sp., process limitations exist with regards to low product yields and inherent production variability. A variety of strategies are being developed to overcome these limitations including elicitation, in situ product removal and metabolic engineering with single genes and transcription factors. Recently, the plant cell culture production platform has been extended to pharmaceutically active heterologous proteins. Plant systems are beneficial because they are able to produce complex proteins that are properly glycosylated, folded and assembled without the risk of contamination by toxins that are associated with mammalian or microbial production systems. Additionally, plant cell culture isolates transgenic material from the environment, allows for more controllable conditions over field-grown crops and promotes secretion of proteins to the medium, reducing downstream purification costs. Despite these benefits, the increase in cost of heterologous protein synthesis in plant cell culture as opposed to field-grown crops is significant and therefore processes must be optimized with regard to maximizing secretion and enhancing protein stability in the cell culture media. This review discusses recent advancements in plant cell culture processing technology, focusing on progress towards overcoming the problems associated with commercialization of these production systems and highlighting recent commercial successes.

Chemical inhibitors suggest endophytic fungal paclitaxel is derived from both mevalonate and non-mevalonate-like pathways

Taxus trees possess fungal endophytes reported to produce paclitaxel. Inhibitors that block early steps in plant paclitaxel biosynthesis were applied to a paclitaxel-producing fungus to determine whether these steps are shared. The plant paclitaxel backbone is reportedly derived from the non-mevalonate terpenoid pathway, while the side chain is phenylalanine-derived. Evidence that the shikimate pathway contributes to fungal paclitaxel was shown by decreased paclitaxel accumulation following inhibition of phenylalanine ammonia lyase. Expression of another shikimate pathway enzyme, 3-dehydroquinate synthase, coincided with paclitaxel production. The importance of the mevalonate pathway in fungal paclitaxel biosynthesis was shown by inhibition of fungal paclitaxel accumulation using compactin, a specific inhibitor of 3-hydroxy-3-methyl-glutaryl-CoA reductase. Expression of another mevalonate pathway enzyme, 3-hydroxy-3-methyl-glutaryl-CoA synthase, coincided with fungal paclitaxel accumulation. Unexpectedly, results from using fosmidomycin suggested that fungal paclitaxel requires 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR), an enzyme in the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway normally found in bacteria/plants. Additional lines of evidence support this finding; first, a plant DXR antibody recognized a fungal peptide of the correct size; second, expression of an apparent fungal DXR ortholog correlated to changes in paclitaxel production; finally, BLAST searching identified a gene putatively encoding 1-deoxy-D-xylulose-5-phosphate synthase, the first enzyme in the MEP pathway in Aspergillus.

Ultrasound-potentiated salicylic acid-induced physiological effects and production of taxol in hazelnut (Corylus avellana L.) cell culture

Effects of ultrasound (US), salicylic acid (SA) and their combined use on the growth and secondary metabolite production of suspension-cultured Corylus avellana cells were investigated. The cultures were treated with US (40 kHz) for short periods of time (2, 3, 5 and 10 min) and SA (25 and 50 mg L(-1)). Results showed that although phenolic content of the cells was significantly increased under exposure to treatments, flavonoids content significantly decreased. Taxol biosynthesis was improved by all treatments. US exposure increased the extracellular, cell-associated and total taxol yield three-, 1.6-, and two-fold compared with that of the control, respectively. SA at all levels was more effective than US in stimulating cell-associated and total taxol production. Combined treatment of US and SA at 50 mg L(-1) resulted in the most improvement in total taxol production, which was about seven times higher than that of the US, three times higher than that of the SA and 14 times higher than that of the control. The results suggest a synergism between US and SA in enhancing taxol production by hazelnut cells.

Asymmetric somatic hybridization between Bupleurum scorzonerifolium Willd. and Taxus chinensis var. mairei

In an attempt to transfer the genetic components needed for taxol synthesis into a more tractable plant, protoplasts of Taxus chinensis var. mairei were UV irradiated for various times prior to their fusion with protoplasts of Bupleurum scorzonerifolium. Of the 60 presumptive hybrid calli obtained, selections of the 9 most rapidly growing were recognized as hybrid clones based on a combination of their callus morphology, esterase profile, chromosome number, and RAPD genotype. The RAPD data showed that 82.4-96.8% of the hybrid genome was inherited from the recipient (B. scorzonerifolium) and 4.6-13.9% from the donor (T. chinensis), with 1.6-6.9% of the RAPD fragments being not present in either parent. None of the hybrid clones expressed a detectable quantity of taxol, but four produced more of the triterpenoid oleanolic acid than did calli of the recipient. With the use of semi-quantitative reverse transcriptase PCR, it was possible to show variation in the expression of several triterpenoid biosynthetic pathway related genes between B. scorzonerifolium and the hybrids. Increasing the concentration of oleanolic acid requires that the expression levels of the genes encoding IPP isomerase, squalene synthase, squalene epoxidase and β-amyrin synthase are increased, while at the same time, those of the genes encoding the branching enzymes cycloartenol synthase and lupeol synthase need to be reduced.

[Screening of high taxol producing fungi by mutagenesis and construction of subtracted cDNA library by suppression subtracted hybridization for differentially expressed genes]

OBJECTIVE

To screen mutants with high yield of taxol, and construct cDNA subtractive library of obtained mutant and primary strain HD(1-3).

METHODS

The spores of taxol-producing fungus HD(1-3) were treated by diethyl sulphate (DES), ultraviolet radiation and diethyl sulphate (UV + DES). cDNA subtractive library of taxol producing fungi from the mRNA of obtained mutant with high yield of taxol tester and HD(1-3) driver was constructed by using suppression subtracted hybridization (SSH).

RESULTS

The optimal conditions for mutagenesis of strain HD(1-3) were as follows: the spore suspension was treated with 8% DES for 15 min, followed by UV irradiation (30 w, 30 cm distance) for 45 sec under magnetic stirring, a mutant UD(14-1) which was able to produce taxol with high yield and could be stably passed on genetics was found. Its ability to produce taxol was improved from 232.73 +/- 4.61 microg/L (strain HD(1-3)) to 312.81 +/- 7.51 microg/L (strain UD(14-1)). The tilter of the constructed cDNA library was 1.2 x 10(7) cfu/mL, the recombinant rate reached to 75.3% and the length of the inserted fragments was mostly 300 bp-1.0 kb.

CONCLUSION

A mutant UD(14-11) with high yield was obtained, and cDNA subtractive library of the mutant UD(14-11) and strain HD(1-3) was constructed. The study laid solid foundation for isolation of taxol biosynthesis related genes and construction of engineering strains with high yield of taxol by genetic techniques.

Transcriptome analysis of Taxus cuspidata needles based on 454 pyrosequencing

Taxus species are highly valued as renewable resources for the production of Taxol. Despite the commercial and medicinal importance of Taxus, little genomic information is available for yew species, and Taxol biosynthesis still needs to be fully elucidated. In this study, 454 pyrosequencing technology was employed to produce an expressed sequence tag (EST) from the needles of Taxus cuspidata. In all, 81 148 high-quality reads from the needles of T. cuspidata were produced using Roche GS FLX Titanium. A total of 20,557 unique sequences were obtained, including 12 975 singletons and 7582 contigs. Approximately 14,095 unique sequences were annotated by a similarity search against five public databases. Gene ontology revealed 11,220 unique sequences that could be assigned to 45 vocabularies. In the Kyoto Encyclopedia of Genes and Genomes mapping, 2403 transcripts were established as associated with 3821 biochemical pathways. Enzymes in the plastidial 2-C-methyl-D-erythritol 4-phosphate pathway were well represented. Candidates of the putative genes of Taxol biosynthesis were revealed, including those in the remaining steps. In total, 291 transcripts were identified, representing putative homologues of transcription factors. Furthermore, 753 simple sequence repeat motifs, which are potential molecular markers for genetic application, were identified. These results provide the largest EST collections in TAXUS and will contribute to biosynthetic and biochemical studies that lead to drug improvement.

4-Deacetylbaccatin III: a proposed biosynthetic precursor of paclitaxel from the bark of Taxus wallichiana

4-Deacetylbaccatin III was isolated and characterized from the bark of Taxus wallichiana Zucc. It was previously identified as an intermediate during the synthesis of paclitaxel and was proposed as a precursor for the biosynthesis of paclitaxel. Existence of 4-deacetylbaccatin III in T. wallichiana is strong evidence for the previously proposed biosynthetic pathway of paclitaxel via 4-deacetylbaccatin III.

Taxus globosa S. cell lines: initiation, selection and characterization in terms of growth, and of baccatin III and paclitaxel production

Of the initial six cell lines originating from explants of Taxus globosa, or Mexican yew (stem internode, leaves and meristematic tissue), three were selected for their microbial and oxidation resistance, two from leaves and the other from stem internode. A study of their behavior, both in terms of cell growth, and of baccatin III and paclitaxel production, was developed in suspension cultures with an initially standardized biomass (fresh weight 0.23 g/L) using modified Gamborg's B5 medium, and an elicitor (methyl jasmonate), on either the first or seventh day of culture, at several levels (0, 0.1, 1, 10, 100 microM). In most of the conditions used, the three cell lines showed growth associated baccatin III production. The cell line from stem internode was the highest producer of baccatin III using 1 microM elicitor, sampling at 10 days (p < or = 0.01, 6.45 mg/L). This same line also had the highest biomass production (6.85 g/L, p < or = 0.01) at 10 days of culture but at the higher elicitor concentration of 10 microM. All three cell lines did not produce paclitaxel under experimental conditions used.

A review: recent advances and future prospects of taxol-producing endophytic fungi

In the urgent search for more effective ways to treat cancer, new extraction methods of taxol from endophytic fungus have demonstrated high potential in increasing the efficiency of taxol extraction for more efficient and sustainable production of taxol and cancer treatment products. This paper summarizes recent advances in taxol-producing endophytic fungi, both in China and abroad, in the following areas: isolation and identification of endophytic fungi types, extraction and detection methods of endophytic taxol in plants, and improved efficiency of the extraction process. With the advancement of science and technology, new techniques in biotechnology, such as fungal strain improvement and recombining technique and microbial fermentation engineering, have increased the extraction yield from taxol-producing fungi, thereby improved the overall efficiency of taxol production.

Recent advances in plant biotechnology and genetic engineering for production of secondary metabolites

For a long time people are using plants not only as crop cultures but also for obtaining of various chemicals. Currently plants remain one of the most important and essential sources of biologically active compounds in spite of progress in chemical or microbial synthesis. In our review we compare potentials and perspectives of modern genetic engineering approaches for pharmaceutical biotechnology and give examples of actual biotechnological systems used for production of several promising natural compounds: artemisinin, paclitaxel and scopolamine.

Taxomyces andreanae: a presumed paclitaxel producer demystified?

The 1990s brought an abundance of reports on paclitaxel-producing endophytes, initially heralded as a discovery having tremendous implications for cancer therapy. As the vision of large-scale fermentation tanks producing vast quantities of relatively inexpensive paclitaxel and novel taxanes has faded and has been replaced by controversial silence, we carried out an in-depth investigation of Taxomyces andreanae - the very first presumed endophytic synthesizer of the diterpenoid. On one hand, metabolic profiling by means of chromatographic, spectroscopic and immunoenzymatic techniques predominant in literature was taken up. On the other, the experimental procedure was brought to an alternative, previously unattempted level aiming at revealing the genetic background of paclitaxel biosynthesis in the endophyte. The profound PCR-based screening for taxadiene synthase (TXS) - a gene unique to the formation of the primary taxane-skeleton, as well as phenylpropanoyl transferase (BAPT) encoding for the catalyst of the final acylation of the core structure rendering the ultimate efficacy of the drug, confirmed the molecular blueprint for paclitaxel biosynthesis to be an inherent genetic trait of the endophyte. However, as the thorough metabolic analysis of Taxomyces andreanae commercial isolate brought no confirmation of endophytic paclitaxel production even after considerable up-scaling endeavors, we postulate that proclaiming the strain "a fungus factory for Taxol" might have been premature.

Taxol biosynthesis: Identification and characterization of two acetyl CoA:taxoid-O-acetyl transferases that divert pathway flux away from Taxol production

Two cDNAs encoding taxoid-O-acetyl transferases (TAX 9 and TAX 14) were obtained from a previously isolated family of Taxus acyl/aroyl transferase cDNA clones. The recombinant enzymes catalyze the acetylation of taxadien-5alpha,13alpha-diacetoxy-9alpha,10beta-diol to generate taxadien-5alpha,10beta,13alpha-tri-acetoxy-9alpha-ol and taxadien-5alpha,9alpha,13alpha-triacetoxy-10beta-ol, respectively, both of which then serve as substrates for a final acetylation step to yield taxusin, a prominent side-route metabolite of Taxus. Neither enzyme acetylate the 5alpha- or the 13alpha-hydroxyls of taxoid polyols, indicating that prior acylations is required for efficient peracetylation to taxusin. Both enzymes were kinetically characterized, and the regioselectivity of acetylation was shown to vary with pH. Sequence comparison with other taxoid acyl transferases confirmed that primary structure of this enzyme type reveals little about function in taxoid metabolism. Unlike previously identified acetyl transferases involved in Taxol production, these two enzymes appear to act exclusively on partially acetylated taxoid polyols to divert the Taxol pathway to side-route metabolites.

A new endophytic taxane-production fungus from Taxus chinensis

More than 50 kinds of endophytic fungi associated with Taxus chinensis, were isolated and examined as potential source of the imposing anticancer drug taxol. Of these, 4 isolates show ability to produce taxane when measured with the competitive inhibition enzyme immunoassay method. The most promising clone, DA10, identified as Mucor rouxianus sp., is the first rouxianus reported as taxol-production fungus. The presence of taxol and its important precursors, such as 10-diacetyl baccatinIII (10-DAB) and baccatinIII, in the culture of this fungus was confirmed by reactivity with taxane-specific monoclonal antibody, comparative chromatographic and mass spectrometric behavior, cytotoxity to liver carcinoma 7402, and molecular cloning of kernel fragment of taxadiene synthase gene.

[Isolation and identification of a taxol-producing endophytic fungus from Podocarpus]

OBJECTIVE

Endophytic fungi can produce beneficial active components during symbiosis with host plants. We isolated a taxol-producing endophytic fungus strain from Podocrapus.

METHODS

The anti-tumor activity of the endophytic funguswas detected by Methyl Thiazolyl Tetrazolium (MTT) method with Vero cells. The production of taxol by one fungus was confirmed by thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). This strain was classified by morphology together with similarity of internal transcribed spacer (ITS) sequence by Clustal W method. The deduced apoptosis of taxol produced from the strain was detected by fluorescent staining method with Vero cells.

RESULTS

A total of 155 endophytic fungi were isolated from the tissue of Podocrapus. The result showed that 28 strains inhibited the growth of Vero cell (inhibitory ratio > or = 10%), and 7 strains had high activity (inhibitory ratio > or = 70%). The taxol-producing ability of strain A2 was confirmed by TLC and HPLC. Therefore, we recognized strain A2 as an endophytic fungus capable of producing taxol from Podocrapus-1 and named it EPTP-1. Its output of taxol was 0.56 mg/L when growing in liquid potato dextrose medium. EPTP-1 was classified as Aspergillus fumigates. Taxol extracted from strain EPTP-1 resulted in significant apoptosis of Vero cells at concentration of 5.553 microg/L for 24h. The activity of anti-Vero growth by extracts from strain EPTP-1 was similar to that of the purchased standard taxol (P > 0.05).

CONCLUSION

The identified endophytic fungus, strain EPTP-1, can be a candidate for taxol production.

CYP725A4 from yew catalyzes complex structural rearrangement of taxa-4(5),11(12)-diene into the cyclic ether 5(12)-oxa-3(11)-cyclotaxane

Taxa-4(5),11(12)-diene is the first committed precursor of functionalized taxanes such as paclitaxel, a successful anticancer drug. Biosynthesis of taxanes in yew involves several oxidations, a number of which have been shown to be catalyzed by cytochrome P-450 oxygenases. Hydroxylation of the C-5alpha of taxa-4(5),11(12)-diene is believed to be the first of these oxidations, and a gene encoding a taxa-4(5),11(12)-diene 5alpha-hydroxylase (CYP725A4) was recently described (Jennewein, S., Long, R. M., Williams, R. M., and Croteau, R. (2004) Chem. Biol. 11, 379-387). In an attempt to produce the early components of the paclitaxel pathway by a metabolic engineering approach, cDNAs encoding taxa-4(5),11(12)-diene synthase and CYP725A4 were introduced in Nicotiana sylvestris for specific expression in trichome cells. Their co-expression did not lead to the production of the expected 5alpha-hydroxytaxa-4(20),11(12)-diene. Instead, taxa-4(5),11(12)-diene was quantitatively converted to a novel taxane that was purified and characterized. Its structure was determined by NMR analysis and found to be that of 5(12)-oxa-3(11)-cyclotaxane (OCT) in which the eight-carbon B-ring from taxa-4(5),11(12)-diene is divided into two fused five-carbon rings. In addition, OCT contains an ether bridge linking C-5 and C-12 from opposite sides of the molecule. OCT was also the sole major product obtained after incubation of taxa-4(5),11(12)-diene with NADPH and microsomes prepared from recombinant yeast expressing CYP725A4. The rearrangement of the taxa-4(5),11(12)-diene ring system is thus mediated by CYP725A4 only and does not rely on additional enzymes or factors present in the plant. The complex structure of OCT led us to propose a reaction mechanism involving a sequence of events so far unknown in P-450 catalysis.