Elicitors Derived from Hazel (Corylus avellana L.) Cell Suspension Culture Enhance Growth and Paclitaxel Production of Epicoccum nigrum

The microbial fermentation is considered as the potential source for large-scale production of paclitaxel. Since co-cultivation/mixed fermentation strategy has been reported as a yield enhancement strategy for paclitaxel production, investigation of fungal endophyte response to plant culture medium, plant cell extract (CE) and medium filtrate (MF) of plant cell suspension culture in terms of growth and paclitaxel production is interesting. In this study, 35 endophytic fungi were isolated from Taxus baccata and Corylus avellana grown in Iran. The analysis of high-performance liquid chromatography and mass spectrometry showed that one isolate (YEF2) produced paclitaxel. The isolate YEF2 was identified as Epicoccum nigrum by sequencing of ITS1-5.8S-ITS2 rDNA region and actin gene. YEF2 was slow-growing in Murashige and Skoog medium, but the synergistic interaction of gibberellic acid (GA3) and CE of C. avellana enhanced the growth of YEF2. The highest total yield of paclitaxel (314.7 µg/l; 11.5-folds) of E. nigrum strain YEF2 was obtained by using 28% (v/v) filter sterilized CE of C. avellana and 2 µg ml-1 GA3 that was significantly higher than the control. In this study, the effects of the plant cell extract on growth and paclitaxel production of paclitaxel producing endophytic fungus were studied for the first time.

Specialized Plant Metabolism Characteristics and Impact on Target Molecule Biotechnological Production

Plant secondary metabolism evolved in the context of highly organized and differentiated cells and tissues, featuring massive chemical complexity operating under tight environmental, developmental and genetic control. Biotechnological demand for natural products has been continuously increasing because of their significant value and new applications, mainly as pharmaceuticals. Aseptic production systems of plant secondary metabolites have improved considerably, constituting an attractive tool for increased, stable and large-scale supply of valuable molecules. Surprisingly, to date, only a few examples including taxol, shikonin, berberine and artemisinin have emerged as success cases of commercial production using this strategy. The present review focuses on the main characteristics of plant specialized metabolism and their implications for current strategies used to produce secondary compounds in axenic cultivation systems. The search for consonance between plant secondary metabolism unique features and various in vitro culture systems, including cell, tissue, organ, and engineered cultures, as well as heterologous expression in microbial platforms, is discussed. Data to date strongly suggest that attaining full potential of these biotechnology production strategies requires being able to take advantage of plant specialized metabolism singularities for improved target molecule yields and for bypassing inherent difficulties in its rational manipulation.

Transcriptome-wide identification and screening of WRKY factors involved in the regulation of taxol biosynthesis in Taxus chinensis

WRKY, a plant-specific transcription factor family, plays important roles in pathogen defense, abiotic cues, phytohormone signaling, and regulation of plant secondary metabolism. However, little is known about the roles, functions, and mechanisms of WRKY in taxane biosynthesis in Taxus spp. In this study, 61 transcripts were identified from Taxus chinensis transcriptome datasets by using hidden Markov model search. All of these transcripts encoded proteins containing WRKY domains, which were designated as TcWRKY1-61. After phylogenetic analysis of the WRKY domains of TcWRKYs and AtWRKYs, 16, 8, 10, 14, 5, 7, and 1 TcWRKYs were cladded into Group I, IIa-IIe, and III, respectively. Then, six representative TcWRKYs were selected to classify their effects on taxol biosynthesis. After MeJA (methyl jasmonate acid) and SA (salicylic acid) treatments, all of the six TcWRKYs were upregulated by MeJA treatment. TcWRKY44 (IId) and TcWRKY47 (IIa) were upregulated, whereas TcWRKY8 (IIc), TcWRKY20 (III), TcWRKY26 (I), TcWRKY41 (IIe), and TcWRKY52 (IIb) were downregulated by SA treatment. Overexpression experiments showed that the six selected TcWRKYs exerted different effects on taxol biosynthesis. In specific, TcWRKY8 and TcWRKY47 significantly improved the expression levels of taxol-biosynthesis-related genes. Transcriptome-wide identification of WRKY factors in Taxus not only enhances our understanding of plant WRKY factors but also identifies candidate regulators of taxol biosynthesis.

Transcriptome profiling reveals specific patterns of paclitaxel synthesis in a new Taxus yunnanensis cultivar

The difference in contents of paclitaxel and 10-deacetylbaccatin III (10-DABIII) in needles between wildtype (WT) and a new cultivar (Zhongdayihao, ZD1) of Taxus yunnanensis was examined. Transcriptome profiling was conducted for different tissues of the ZD1 and WT to illustrate the regulation mechanism of paclitaxel biosynthesis. It was observed that average contents of paclitaxel and 10-DABIII in ZD1 were 4 folds and 32 folds higher than those in WT, respectively. More significant elevations of differential expressed genes (DEGs) from paclitaxel biosynthesis pathway were revealed in ZD1 rather than WT, which should be responsible for the higher contents of paclitaxel and 10-DABIII in the ZD1. Special tissues-dependent expression patterns of paclitaxel biosynthesis DEGs in ZD1 compared to WT were unraveled. The relative higher expressions of paclitaxel biosynthesis genes in needles than other tissues supported the higher content of paclitaxel and 10-DABIII content in needles of ZD1. Attenuation of plant hormone signal transduction pathway led to the lower expression of TFs in ZD1 rather than WT. Besides, the significant negative correlations between differential expressed TFs and DEGs from paclitaxel biosynthesis pathway displayed a possibly negative regulation pattern of these TFs on paclitaxel biosynthesis pathway genes. These results provided new insights into the molecular process of paclitaxel synthesis in Taxus.

[Identification and characterization of a taxol-producing endophytic fungus from Taxus media]

To enrich the resource pool of endophytic fungi from plants which produce taxol, a taxol-producing endophytic fungus TMS-26 was isolated from the stem of Taxus Media. The result of high performance liquid chromatography (HPLC) showed that TMS-26 extract exhibited similar chromatographic peaks and retention time (4.545 min) with authentic taxol. Then mass spectrometry (MS) analysis further confirmed that TMS-26 extracts contained the same mass peaks with authentic taxol ((M+Na)+=876). These indicated that the isolated endophytic fungus TMS-26 can produce taxol. According to the morphological characteristics, the molecular analysis of 18S rDNA and internal transcribed spacer nuclear rDNA gene sequence, the fungus was identified as Aspergillus fumigatus TMS-26.

Comparative proteomic analyses of two Taxus species (Taxus × media and Taxus mairei) reveals variations in the metabolisms associated with paclitaxel and other metabolites

Taxus species are well-known for paclitaxel, which exhibits antitumor activities and is used for treating various cancers. Although most Taxus species are widespread in many areas, few studies have characterized the variation in metabolism among different Taxus species. Using an integrated approach involving 'tandem mass tag' labeling and liquid chromatography-tandem mass spectrometry (HPLC-MS), proteomes of T. media and T. mairei were investigated and 4078 proteins were quantified. Screening and classification of differentially expressed proteins revealed many metabolism-associated proteins. In detail, four enzymes involved in the flavonoid biosynthesis pathway were predominantly expressed in T. mairei. Four enzymes associated with supplying precursors for paclitaxel biosynthesis and three cytochrome P450 taxoid oxygenases were preferentially expressed in T. media compared with T. mairei. Furthermore, variations in taxoid contents between T. media and T. mairei were determined using HPLC-MS analysis. Variations in flavonoid contents between T. media and T. mairei were determined by HPLC analysis. A number of differentially expressed proteins may provide an explanation for the variation in metabolisms of different Taxus species.

An endophytic fungus efficiently producing paclitaxel isolated from Taxus wallichiana var. mairei

Paclitaxel is a medicinal ingredient with high anticancer activity and widely used in hospitals and clinics. In this study, we isolate endophytic fungi efficiently producing paclitaxel from yew for the purpose of paclitaxel manufacture.The bark of Taxus wallichiana var. mairei was surface sterilized and then inoculated in potato dextrose agar culture medium to isolate endophytic fungi. The paclitaxel in the fungal culture was extracted with mixture of chloroform and the same amount of methanol. The content of paclitaxel in the extract was determined and identified with LC-MS. The endophytic fungus efficiently producing paclitaxel was species identified with ITS rDNA and 26S D1/D2 rDNA sequencing.There were 528 endophytic fungal strains were isolated from the bark of T wallichiana var. mairei in total. There was only a strain efficiently producing paclitaxel in these endophytic fungi. The unique strain was identified as Phoma medicaginis. The paclitaxel contents in whole potato dextrose broth (PDB) culture, spent culture medium from this strain and that in dry mycelium is 1.215 mg/L, 0.936 mg/L, and 20 mg/kg, respectively.An endophytic fungus efficiently producing paclitaxel was isolated from T wallichiana var. mairei. This isolated endophytic fungus can be used as a producing strain for paclitaxel manufacture.

An endophytic Basidiomycete, Grammothele lineata, isolated from Corchorus olitorius, produces paclitaxel that shows cytotoxicity

Grammothele lineata, an endophyte isolated in our laboratory from jute (Corchorus olitorius acc. 2015) was found to be a substantial paclitaxel producer. Taxol and its related compounds, produced by this endophyte were extracted by growing the fungus in simple nutrient media (potato dextrose broth, PDB). Taxol was identified and characterized by different analytical techniques (TLC, HPLC, FTIR, LC-ESI-MS/MS) following its extraction by ethyl acetate. In PDB media, this fungus was found to produce 382.2 μgL-1 of taxol which is about 7.6 x103 fold higher than the first reported endophytic fungi, Taxomyces andreanae. The extracted taxol exhibited cytotoxic activity in an in vitro culture of HeLa cancer cell line. The fungal extract also exhibited antifungal and antibacterial activities against different pathogenic strains. This is the first report of a jute endophytic fungus harboring the capacity to produce taxol and also the first reported taxol producing species that belongs to the Basidiomycota phylum, so far unknown to be a taxol producer. These findings suggest that the fungal endophyte, Grammothele lineata can be an excellent source of taxol and can also serve as a potential species for chemical and genetic engineering to enhance further the production of taxol.

Production of paclitaxel with anticancer activity by two local fungal endophytes, Aspergillus fumigatus and Alternaria tenuissima

Among 60 fungal endophytes isolated from twigs, bark, and mature leaves of different plant species, two fungal isolates named TXD105 and TER995 were capable of producing paclitaxel in amounts of up to 84.41 and 37.92 μg L^-1, respectively. Based on macroscopic and microscopic characteristics, ITS1-5.8S-ITS2 rDNA sequence, and phylogenetic characteristic analysis, the two respective isolates were identified as Aspergillus fumigatus and Alternaria tenuissima. In the effort to increase paclitaxel magnitude by the two fungal strains, several fermentation conditions including selection of the proper fermentation medium, agitation rate, incubation temperature, fermentation period, medium pH, medium volume, and inoculum nature (size and age of inoculum) were tried. Fermentation process carried out in M1D medium (pH 6.0) and maintained at 120 rpm for 10 days and at 25 °C using 4% (v/v) inoculum of 5-day-old culture stimulated the highest paclitaxel production to attain 307.03 μg L^-1 by the A. fumigatus strain. In the case of the A. tenuissima strain, fermentation conditions conducted in flask basal medium (pH 6.0) and maintained at 120 rpm for 14 days and at 25 °C using 8% (v/v) inoculum of 7-day-old culture were found the most favorable to attain the highest paclitaxel production of 124.32 μg L^-1. Using the MTT-based assay, fungal paclitaxel significantly inhibited the proliferation of five different cancer cell lines with 50% inhibitory concentration values varied from 3.04 to 14.8 μg mL^-1. Hence, these findings offer new and alternate sources with excellent biotechnological potential for paclitaxel production by fungal fermentation.

[Recent advances in biosynthetic pathway and synthetic biology of taxol]

Taxol, a kind of terpenoid secondary metabolite produced by Taxus brevifolia, is an effective anticancer drug that manufacture relies mainly on the extraction form plants. In order to solve the resource shortage, a lot of work has been done to develop the alternative method. Recently, using synthetic biology to realize heterologous biosynthesis of the precursors of taxol has become a hotspot. Now, the basic framework of taxol biosynthetic pathways has been confirmed, and most enzyme genes involved in taxol biosynthesis have been cloned and identified. The two taxol precursors, taxa-4(5),11(12)-diene and taxa-4(20),11(12)-dien-5α-ol, have been synthesized in Escherichia coli and Saccharomyces cerevisiae. Here this paper reviewed the recent advances in the biosynthetic pathway of taxol and the latest developments of synthetic biology, which aims to provide a guidance for the heterologous biosynthesis of taxol.

Response and Defense Mechanisms of Taxus chinensis Leaves Under UV-A Radiation are Revealed Using Comparative Proteomics and Metabolomics Analyses

Taxus chinensis var. mairei is a species endemic to south-eastern China and one of the natural sources for the anticancer medicine paclitaxel. To investigate the molecular response and defense mechanisms of T. chinensis leaves to enhanced ultraviolet-A (UV-A) radiation, gel-free/label-free and gel-based proteomics and gas chromatography-mass spectrometry (GC-MS) analyses were performed. The transmission electron microscopy results indicated damage to the chloroplast under UV-A radiation. Proteomics analyses in leaves and chloroplasts showed that photosynthesis-, glycolysis-, secondary metabolism-, stress-, and protein synthesis-, degradation- and activation-related systems were mainly changed under UV-A radiation. Forty-seven PSII proteins and six PSI proteins were identified as being changed in leaves and chloroplasts under UV-A treatment. This indicated that PSII was more sensitive to UV-A than PSI as the target of UV-A light. Enhanced glycolysis, with four glycolysis-related key enzymes increased, provided precursors for secondary metabolism. The 1-deoxy-d-xylulose-5-phosphate reductoisomerase and 4-hydroxy-3-methylbut-2-enyl diphosphate reductase were identified as being significantly increased during UV-A radiation, which resulted in paclitaxel enhancement. Additionally, mRNA expression levels of genes involved in the paclitaxel biosynthetic pathway indicated a down-regulation under UV-A irradiation and up-regulation in dark incubation. These results reveal that a short-term high dose of UV-A radiation could stimulate the plant stress defense system and paclitaxel production.

Succinyl-proteome profiling of a high taxol containing hybrid Taxus species (Taxus × media) revealed involvement of succinylation in multiple metabolic pathways

Protein lysine succinylation, a ubiquitous protein post-translational modification among eukaryotic and prokaryotic cells, represents a vital regulator of various metabolic processes. However, little is known about its functions and cellular distribution in Taxus × media, which is a hybrid Taxus species containing a high content of taxol. In this study, LC-MS/MS was used to identify peptides enriched by immune-purification with high-efficiency succinyl-lysine antibody. A total of 193 succinylated proteins and 325 succinylation sites were identified. The bioinformatics analysis indicated that these succinylated proteins were involved in a wide range of cellular functions from metabolism to protein binding and showed diverse subcellular localizations. Furthermore, our findings suggested that lysine succinylation in Taxus × media involved a diverse array of metabolic processes and protein-protein interactions. Many enzymes involved in multiple metabolic pathways, such as glycolysis, pyruvate metabolism, the tricarboxylic acid cycle and carbon fixation, were identified as substrates for lysine succinylation, suggesting the presence of a common mechanism underlying the participation of succinylation in metabolic regulation. These results provide the first comprehensive view of the succinylome of Taxus × media and may catalyze future biological investigation of succinylation.

Transcript profiling of jasmonate-elicited Taxus cells reveals a β-phenylalanine-CoA ligase

Plant cell cultures constitute eco-friendly biotechnological platforms for the production of plant secondary metabolites with pharmacological activities, as well as a suitable system for extending our knowledge of secondary metabolism. Despite the high added value of taxol and the importance of taxanes as anticancer compounds, several aspects of their biosynthesis remain unknown. In this work, a genomewide expression analysis of jasmonate-elicited Taxus baccata cell cultures by complementary DNA-amplified fragment length polymorphism (cDNA-AFLP) indicated a correlation between an extensive elicitor-induced genetic reprogramming and increased taxane production in the targeted cultures. Subsequent in silico analysis allowed us to identify 15 genes with a jasmonate-induced differential expression as putative candidates for genes encoding enzymes involved in five unknown steps of taxane biosynthesis. Among them, the TB768 gene showed a strong homology, including a very similar predicted 3D structure, with other genes previously reported to encode acyl-CoA ligases, thus suggesting a role in the formation of the taxol lateral chain. Functional analysis confirmed that the TB768 gene encodes an acyl-CoA ligase that localizes to the cytoplasm and is able to convert β-phenylalanine, as well as coumaric acid, into their respective derivative CoA esters. β-phenylalanyl-CoA is attached to baccatin III in one of the last steps of the taxol biosynthetic pathway. The identification of this gene will contribute to the establishment of sustainable taxol production systems through metabolic engineering or synthetic biology approaches.

Two jasmonate-responsive factors, TcERF12 and TcERF15, respectively act as repressor and activator of tasy gene of taxol biosynthesis in Taxus chinensis

Methyl jasmonate (MeJA) is one of the most effective inducers of taxol biosynthetic genes, particularly the tasy gene. However, the mechanism underlying the regulation of tasy by MeJA is still unknown. In this study, a 550-bp 5'-flanking sequence was obtained and confirmed as the promoter of the tasy gene. Deletion analysis revealed that the fragment containing a GCC-box from -150 to -131 was the crucial jasmonate (JA)-responsive element, designated as JRE. Using JRE as bait, two binding proteins, namely TcERF12 and TcERF15, were discovered. Sequence alignment and phylogenetic analysis showed that TcERF12 was related to the repressor AtERF3, while TcERF15 was more related to the activator ORA59; these are typical GCC-box-binding ethylene-responsive factors. Both could significantly respond to MeJA for 10 and 4.5 times, respectively, in 0.5 h. When the two TcERFs were overexpressed in Taxus cells, tasy gene expression decreased by 2.1 times in TcERF12-overexpressing cells, but increased by 2.5 times in TcERF15-overexpressing cells. Results indicated that TcERF12 and TcERF15 were negative and positive regulators, respectively, in the JA signal transduction to the tasy gene by binding the GCC-box in the JRE of the tasy promoter. Our results promote further research on regulatory mechanisms of taxol biosynthesis.

Two jasmonate-responsive factors, TcERF12 and TcERF15, respectively act as repressor and activator of tasy gene of taxol biosynthesis in Taxus chinensis

Methyl jasmonate (MeJA) is one of the most effective inducers of taxol biosynthetic genes, particularly the tasy gene. However, the mechanism underlying the regulation of tasy by MeJA is still unknown. In this study, a 550-bp 5'-flanking sequence was obtained and confirmed as the promoter of the tasy gene. Deletion analysis revealed that the fragment containing a GCC-box from -150 to -131 was the crucial jasmonate (JA)-responsive element, designated as JRE. Using JRE as bait, two binding proteins, namely TcERF12 and TcERF15, were discovered. Sequence alignment and phylogenetic analysis showed that TcERF12 was related to the repressor AtERF3, while TcERF15 was more related to the activator ORA59; these are typical GCC-box-binding ethylene-responsive factors. Both could significantly respond to MeJA for 10 and 4.5 times, respectively, in 0.5 h. When the two TcERFs were overexpressed in Taxus cells, tasy gene expression decreased by 2.1 times in TcERF12-overexpressing cells, but increased by 2.5 times in TcERF15-overexpressing cells. Results indicated that TcERF12 and TcERF15 were negative and positive regulators, respectively, in the JA signal transduction to the tasy gene by binding the GCC-box in the JRE of the tasy promoter. Our results promote further research on regulatory mechanisms of taxol biosynthesis.

[Cloning and functional characterization of a cDNA encoding isopentenyl diphosphate isomerase involved in taxol biosynthesis in Taxus media]

Taxol is one of the most potent anti-cancer agents, which is extracted from the plants of Taxus species. Isopentenyl diphosphate isomerase (IPI) catalyzes the reversible transformation between IPP and DMAPP, both of which are the general 5-carbon precursors for taxol biosynthesis. In the present study, a new gene encoding IPI was cloned from Taxus media (namely TmIPI with the GenBank Accession Number KP970677) for the first time. The full-length cDNA of TmIPI was 1 232 bps encoding a polypeptide with 233 amino acids, in which the conserved domain Nudix was found. Bioinformatic analysis indicated that the sequence of TmIPI was highly similar to those of other plant IPI proteins, and the phylogenetic analysis showed that there were two clades of plant IPI proteins, including IPIs of angiosperm plants and IPIs of gymnosperm plants. TmIPI belonged to the clade of gymnosperm plant IPIs, and this was consistent with the fact that Taxus media is a plant species of gymnosperm. Southern blotting analysis demonstrated that there was a gene family of IPI in Taxus media. Finally, functional verification was applied to identify the function of TmIPI. The results showed that biosynthesis of β-carotenoid was enhanced by overexpressing TmIPI in the engineered E. coli strain, and this suggested that TmIPI might be a key gene involved in isoprenoid/terpenoid biosynthesis.

Pilot studies on scale-up biocatalysis of 7-β-xylosyl-10-deacetyltaxol and its analogues by an engineered yeast

Paclitaxel content in yew tree is extremely low, causing a worldwide shortage of this important anticancer drug. Yew tree can also produce abundant 7-β-xylosyl-10-deacetyltaxol that can be bio-converted into 10-deacetyltaxol for semi-synthesis of paclitaxel. However, the bio-conversion by the screened natural microorganisms was inefficient. We have constructed the recombinant yeast with a glycoside hydrolase gene from Lentinula edodes and explored the bioconversion. Based on previously established reaction conditions, the bioconversion of 7-β-xylosyl-10-deacetyltaxol or its extract was further optimized and scaled up with the engineered yeast harvested from 200-L scale high-cell-density fermentation. The optimization included the freeze-dried cell amount, dimethyl sulfoxide concentration, addition of 0.5% antifoam supplement, and substrate concentration. A 93-95% bioconversion and 83% bioconversion of 10 and 15 g/L 7-β-xylosyltaxanes in 10 L reaction volume were achieved, respectively. The yield of 10-deacetyltaxol reached 10.58 g/L in 1 L volume with 15 g/L 7-β-xylosyl-10-deacetyltaxol. The conversion efficiencies were not only much higher than those of other reports and our previous work, but also realized in 10 L reaction volume. A pilot-scale product purification was also established. Our study bridges the gap between the basic research and commercial utilization of 7-β-xylosyl-10-deacetyltaxol for the industrial production of semi-synthetic paclitaxel.

Baseline survey of root-associated microbes of Taxus chinensis (Pilger) Rehd

Taxol (paclitaxel) a diterpenoid is one of the most effective anticancer drugs identified. Biosynthesis of taxol was considered restricted to the Taxus genera until Stierle et al. discovered that an endophytic fungus isolated from Taxus brevifolia could independently synthesize taxol. Little is known about the mechanism of taxol biosynthesis in microbes, but it has been speculated that its biosynthesis may differ from plants. The microbiome from the roots of Taxus chinensis have been extensively investigated with culture-dependent methods to identify taxol synthesizing microbes, but not using culture independent methods.,Using bar-coded high-throughput sequencing in combination with a metagenomics approach, we surveyed the microbial diversity and gene composition of the root-associated microbiomefrom Taxus chinensis (Pilger) Rehd. High-throughput amplicon sequencing revealed 187 fungal OTUs which is higher than any previously reported fungal number identified with the culture-dependent method, suggesting that T. chinensis roots harbor novel and diverse fungi. Some operational taxonomic units (OTU) identified were identical to reported microbe strains possessing the ability to synthesis taxol and several genes previously associated with taxol biosynthesis were identified through metagenomics analysis.

De Novo characterization of a Cephalotaxus hainanensis transcriptome and genes related to paclitaxel biosynthesis

Cephalotaxus hainanensis, an endangered plant, is known to contain several metabolites with anti-cancer activity. Despite its clinical impact, the alkaloid metabolism of this species has remained largely uncharacterized. The potential of Cephalotaxus for metabolic engineering of medically interesting compounds has, so far, not been exploited, due to the almost complete lack of molecular information. We have therefore performed a high throughput RNA-seq analysis and assembled the transcriptome de novo. Raw reads comprising 4.3 Gbp were assembled de novo into 39,416 unique sequences (unigenes) with a mean length of 1,089.8 bp and a total assembly size of 45.8 Mbp, which equals to more than 50 times the number of Cephalotaxaceae sequences currently deposited in the GenBank (as of August 2013). As proof of principle for medically interesting pathways, gene fragments related to paclitaxel biosynthesis were searched and detected. To verify their functionality, the metabolic product paclitaxel, and its precursor baccatin III, were identified in the leaves of C. hainanensis by HPLC, and shown to be induced by MeJA. This finding demonstrates exemplarily the potential of the annotated transcriptome as information resource for the biotechnological exploitation of plant secondary metabolism.

Bioproduction of baccatin III, an advanced precursor of paclitaxol, with transgenic Flammulina velutipes expressing the 10-deacetylbaccatin III-10-O-acetyl transferase gene

BACKGROUND

10-Deacetylbaccatin III (10-DAB) and baccatin III are intermediates in the biosynthesis of Taxol (an anti-cancer drug) and useful precursors for semi-synthesis of the drug. In this study, a bioconversion system was established for the production of baccatin III, an advanced precursor of paclitaxel, in the transgenic mushroom Flammulina velutipes expressing the 10-deacetylbaccatin III-10β-O-acetyltransferase gene. The expression vector pgFvs-TcDBAT containing the 10-deacetylbaccatin III-10β-O-acetyltransferase (DBAT) gene was constructed and transformed into the cells of F. velutipes by polyethylene glycol-mediated protoplast transformation.

RESULTS

Polymerase chain reaction and Southern blotting analysis verified the successful integration of the exogenous DBAT gene into the genome of F. velutipes. Reverse transcription polymerase chain reaction and enzyme activity analyses confirmed that the DBAT gene was expressed in F. velutipes, and DBAT is able to convert substrate into baccatin III.

CONCLUSION

The DBAT gene from the plant Taxus chinensis can be functionally expressed in F. velutipes. Transgenic F. velutipes expressing the DBAT gene is able to produce the target product, baccatin III. This is the first report about the transformation and expression of paclitaxel biosynthetic gene in the edible mushroom F. velutipes. This represents a significant step towards bio-production of paclitaxel and its advanced precursor baccatin III in an edible fungus.

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.