Iso-Seq analysis of the Taxus cuspidata transcriptome reveals the complexity of Taxol biosynthesis

Regulatory microRNAs and phasiRNAs of paclitaxel biosynthesis in Taxus chinensis

Paclitaxel (trade name Taxol) is a rare diterpenoid with anticancer activity isolated from Taxus. At present, paclitaxel is mainly produced by the semi-synthetic method using extract of Taxus tissues as raw materials. The studies of regulatory mechanisms in paclitaxel biosynthesis would promote the production of paclitaxel through tissue/cell culture approaches. Here, we systematically identified 990 transcription factors (TFs), 460 microRNAs (miRNAs), and 160 phased small interfering RNAs (phasiRNAs) in Taxus chinensis to explore their interactions and potential roles in regulation of paclitaxel synthesis. The expression levels of enzyme genes in cone and root were higher than those in leaf and bark. Nearly all enzyme genes in the paclitaxel synthesis pathway were significantly up-regulated after jasmonate treatment, except for GGPPS and CoA Ligase. The expression level of enzyme genes located in the latter steps of the synthesis pathway was significantly higher in female barks than in male. Regulatory TFs were inferred through co-expression network analysis, resulting in the identification of TFs from diverse families including MYB and AP2. Genes with ADP binding and copper ion binding functions were overrepresented in targets of miRNA genes. The miRNA targets were mainly enriched with genes in plant hormone signal transduction, mRNA surveillance pathway, cell cycle and DNA replication. Genes in oxidoreductase activity, protein-disulfide reductase activity were enriched in targets of phasiRNAs. Regulatory networks were further constructed including components of enzyme genes, TFs, miRNAs, and phasiRNAs. The hierarchical regulation of paclitaxel production by miRNAs and phasiRNAs indicates a robust regulation at post-transcriptional level. Our study on transcriptional and posttranscriptional regulation of paclitaxel synthesis provides clues for enhancing paclitaxel production using synthetic biology technology.

Genome-Wide Identification and Expression Pattern Analysis of BAHD Acyltransferase Family in Taxus mairei

BAHD acyltransferases are involved in catalyzing and regulating the secondary metabolism in plants. Despite this, the members of BAHD family and their functions have not been reported in the Taxus species. In this study, a total of 123 TwBAHD acyltransferases from Taxus wallichiana var. mairei genome were identified and divided into six clades based on phylogenetic analysis, of which Clade VI contained a Taxus-specific branch of 52 members potentially involved in taxol biosynthesis. Most TwBAHDs from the same clade shared similar conserved motifs and gene structures. Besides the typical conserved motifs within the BAHD family, the YPLAGR motif was also conserved in multiple clades of T. mairei. Moreover, only one pair of tandem duplicate genes was found on chromosome 1, with a Ka/Ks ratio < 1, indicating that the function of duplicate genes did not differentiate significantly. RNA-seq analysis revealed different expression patterns of TwBAHDs in MeJA induction and tissue-specific expression experiments. Several TwBAHD genes in the Taxus-specific branch were highly expressed in different tissues of T. mairei, suggesting an important role in the taxol pathway. This study provides comprehensive information for the TwBAHD gene family and sets up a basis for its potential functions.

Transcriptome and comparative chloroplast genome analysis of Taxus yunnanensis individuals with high and low paclitaxel yield

Paclitaxel is a potent anti-cancer drug that is mainly produced through semi-synthesis, which still requires plant materials as precursors. The content of paclitaxel and 10-deacetyl baccatin III (10-DAB) in Taxus yunnanensis has been found to differ from that of other Taxus species, but there is little research on the mechanism underlying the variation in paclitaxel content in T. yunnanensis of different provenances. In this experiment, the contents of taxoids and precursors in twigs between a high paclitaxel-yielding individual (TG) and a low paclitaxel-yielding individual (TD) of T. yunnanensis were compared, and comparative analyses of transcriptomes as well as chloroplast genomes were performed. High-performance liquid chromatography (HPLC) detection showed that 10-DAB and baccatin III contents in TG were 18 and 47 times those in TD, respectively. Transcriptomic analysis results indicated that genes encoding key enzymes in the paclitaxel biosynthesis pathway, such as taxane 10-β-hydroxylase (T10βH), 10-deacetylbaccatin III 10-O-acetyltransferase (DBAT), and debenzoyl paclitaxel N-benzoyl transferase (DBTNBT), exhibited higher expression levels in TG. Additionally, qRT-PCR showed that the relative expression level of T10βH and DBAT in TG were 29 and 13 times those in TD, respectively. In addition, six putative transcription factors were identified that may be involved in paclitaxel biosynthesis from transcriptome data. Comparative analysis of plastid genomes showed that the TD chloroplast contained a duplicate of rps12, leading to a longer plastid genome length in TD relative to TG. Fifteen mutation hotspot regions were identified between the two plastid genomes that can serve as candidate DNA barcodes for identifying high-paclitaxel-yield individuals. This experiment provides insight into the difference in paclitaxel accumulation among different provenances of T. yunnanensis individuals.

Integrating Transcriptome and Chemical Analyses to Provide Insights into Biosynthesis of Terpenoids and Flavonoids in the Medicinal Industrial Crop Andrographis paniculate and Its Antiviral Medicinal Parts

Andrographis paniculata is a medicinal plant traditionally used to produce diterpene lactones and flavonoids, which possess various biological activities. Widely distributed in China, India, and other Southeast Asia countries, A. paniculata has become an important economic crop, significantly treating SARS-CoV-2, and is being cultivated on a large scale in southern China. The biosynthesis of active ingredients in A. paniculata are regulated and controlled by genes, but their specific roles are still not fully understood. To further explore the growth regulation factors and utilization of its medicinal parts of this industrial crop, chemical and transcriptome analyses were conducted on the roots, stems, and leaves of A. paniculata to identify the biosynthesis pathways and related candidate genes of the active ingredients. The chemical analysis revealed that the main components of A. paniculata were diterpene lactones and flavonoids, which displayed potential ability to treat SARS-CoV-2 through molecular docking. Moreover, the transcriptome sequencing annotated a total of 40,850 unigenes, including 7962 differentially expressed genes. Among these, 120 genes were involved in diterpene lactone biosynthesis and 60 genes were involved in flavonoid biosynthesis. The expression of diterpene lactone-related genes was the highest in leaves and the lowest in roots, consistent with our content determination results. It is speculated that these highly expressed genes in leaves may be involved in the biosynthesis pathway of diterpenes. Furthermore, two class Ⅰ terpene synthases in A. paniculata transcriptome were also annotated, providing reference for the downstream pathway of the diterpene lactone biosynthesis. With their excellent market value, our experiments will promote the study of the biosynthetic genes for active ingredients in A. paniculata and provide insights for subsequent in vitro biosynthesis.

Identification and Functional Characterization of a Novel Sinapyl Alcohol Acyltransferase from Euphorbia lathyris L

Methoxyeugenol is a phenylpropene compound derived from plants and has various bioactivities. The chemical synthesis of methoxyeugenol is accompanied by pollution issues, whereas extraction from plants is associated with problems such as low yield and high cost. The production of methoxyeugenol can be effectively addressed through an enzymatic approach. In this study, the acyltransferase genes of Euphorbia lathyris L. were screened by homologous alignment of the transcriptome data of E. lathyris in the late growth stage and the acyltransferase genes of the closely related plant species. The results showed that ElBAHD10 had the closest relationship with earlier reported ScCFAT and PhCFAT, which were found to catalyze the reaction of coniferyl alcohol to generate coniferyl acetate. The ElBAHD10 gene was successfully cloned from E. lathyris and subsequently expressed in Escherichia coli. The purified protein ElBAHD10 catalyzed the reaction of sinapyl alcohol with acetyl CoA and cinnamoyl CoA to form sinapyl acetate and sinapyl cinnamate, respectively. In contrast, the crude ElBAHD10 protein could catalyze sinapyl alcohol to directly generate methoxyeugenol. The recombinant E. coli strain expressing ElBAHD10 produced methoxyeugenol through whole-cell transformation. This study provides insights and lays the foundation for methoxyeugenol production through biosynthetic approaches.

Synthetic biology identifies the minimal gene set required for paclitaxel biosynthesis in a plant chassis

The diterpenoid paclitaxel (Taxol) is a chemotherapy medication widely used as a first-line treatment against several types of solid cancers. The supply of paclitaxel from natural sources is limited. However, missing knowledge about the genes involved in several specific metabolic steps of paclitaxel biosynthesis has rendered it difficult to engineer the full pathway. In this study, we used a combination of transcriptomics, cell biology, metabolomics, and pathway reconstitution to identify the complete gene set required for the heterologous production of paclitaxel. We identified the missing steps from the current model of paclitaxel biosynthesis and confirmed the activity of most of the missing enzymes via heterologous expression in Nicotiana benthamiana. Notably, we identified a new C4β-C20 epoxidase that could overcome the first bottleneck of metabolic engineering. We used both previously characterized and newly identified oxomutases/epoxidases, taxane 1β-hydroxylase, taxane 9α-hydroxylase, taxane 9α-dioxygenase, and phenylalanine-CoA ligase, to successfully biosynthesize the key intermediate baccatin III and to convert baccatin III into paclitaxel in N. benthamiana. In combination, these approaches establish a metabolic route to taxoid biosynthesis and provide insights into the unique chemistry that plants use to generate complex bioactive metabolites.

Way to efficient microbial paclitaxel mass production

The microbial synthesis of paclitaxel is attractive for its short-cycle, cost-effectiveness, and sustainability. However, low paclitaxel productivity, depleted capacity during subculture and storage, and unclear biosynthesis mechanisms restrain industrial microbial synthesis. Along with the isolation of various paclitaxel-producing microorganisms and the development of versatile molecular tools, tremendous promises for microbial paclitaxel synthesis have become increasingly prominent. In this review, we summarize the progress of microbial synthesis of paclitaxel in recent years, focusing on paclitaxel-producing endophytes and representative engineering microorganism hosts that were used as chassis for paclitaxel precursor synthesis. Numerous wide-type microbes can manufacture paclitaxel, and fermentation process optimization and strain improvement can greatly enhance the productivity. Engineered microbes can efficiently synthesize precursors of paclitaxel by introducing exogenous synthetic pathway. Mining paclitaxel synthetic pathways and genetic manipulation of endophytes will accelerate the construction of microbial cell factories, indefinitely contributing to paclitaxel mass production by microbes. This review emphasizes the potential and provides solutions for efficient microbial paclitaxel mass production.

Integrated mass spectrometry imaging and single-cell transcriptome atlas strategies provide novel insights into taxoid biosynthesis and transport in Taxus mairei stems

Taxol, which is a widely used important chemotherapeutic agent, was originally isolated from Taxus stem barks. However, little is known about the precise distribution of taxoids and the transcriptional regulation of taxoid biosynthesis across Taxus stems. Here, we used MALDI-IMS analysis to visualize the taxoid distribution across Taxus mairei stems and single-cell RNA sequencing to generate expression profiles. A single-cell T. mairei stem atlas was created, providing a spatial distribution pattern of Taxus stem cells. Cells were reordered using a main developmental pseudotime trajectory which provided temporal distribution patterns in Taxus stem cells. Most known taxol biosynthesis-related genes were primarily expressed in epidermal, endodermal, and xylem parenchyma cells, which caused an uneven taxoid distribution across T. mairei stems. We developed a single-cell strategy to screen novel transcription factors (TFs) involved in taxol biosynthesis regulation. Several TF genes, such as endodermal cell-specific MYB47 and xylem parenchyma cell-specific NAC2 and bHLH68, were implicated as potential regulators of taxol biosynthesis. Furthermore, an ATP-binding cassette family transporter gene, ABCG2, was proposed as a potential taxoid transporter candidate. In summary, we generated a single-cell Taxus stem metabolic atlas and identified molecular mechanisms underpinning the cell-specific transcriptional regulation of the taxol biosynthesis pathway.

Exploring the Interplay between Metabolic Pathways and Taxane Production in Elicited Taxus baccata Cell Suspensions

Taxus cell cultures are a reliable biotechnological source of the anticancer drug paclitaxel. However, the interplay between taxane production and other metabolic pathways during elicitation remains poorly understood. In this study, we combined untargeted metabolomics and elicited Taxus baccata cell cultures to investigate variations in taxane-associated metabolism under the influence of 1 µM coronatine (COR) and 150 µM salicylic acid (SA). Our results demonstrated pleiotropic effects induced by both COR and SA elicitors, leading to differential changes in cell growth, taxane content, and secondary metabolism. Metabolite annotation revealed significant effects on N-containing compounds, phenylpropanoids, and terpenoids. Multivariate analysis showed that the metabolomic profiles of control and COR-treated samples are closer to each other than to SA-elicited samples at different time points (8, 16, and 24 days). The highest level of paclitaxel content was detected on day 8 under SA elicitation, exhibiting a negative correlation with the biomarkers kauralexin A2 and taxusin. Our study provides valuable insights into the intricate metabolic changes associated with paclitaxel production, aiding its potential optimization through untargeted metabolomics and an evaluation of COR/SA elicitor effects.

A long-read and short-read transcriptomics approach provides the first high-quality reference transcriptome and genome annotation for Pseudotsuga menziesii (Douglas-fir)

Douglas-fir (Pseudotsuga menziesii) is native to western North America. It grows in a wide range of environmental conditions and is an important timber tree. Although there are several studies on the gene expression responses of Douglas-fir to abiotic cues, the absence of high-quality transcriptome and genome data is a barrier to further investigation. Like for most conifers, the available transcriptome and genome reference dataset for Douglas-fir remains fragmented and requires refinement. We aimed to generate a highly accurate, and complete reference transcriptome and genome annotation. We deep-sequenced the transcriptome of Douglas-fir needles from seedlings that were grown under nonstress control conditions or a combination of heat and drought stress conditions using long-read (LR) and short-read (SR) sequencing platforms. We used 2 computational approaches, namely de novo and genome-guided LR transcriptome assembly. Using the LR de novo assembly, we identified 1.3X more high-quality transcripts, 1.85X more "complete" genes, and 2.7X more functionally annotated genes compared to the genome-guided assembly approach. We predicted 666 long noncoding RNAs and 12,778 unique protein-coding transcripts including 2,016 putative transcription factors. We leveraged the LR de novo assembled transcriptome with paired-end SR and a published single-end SR transcriptome to generate an improved genome annotation. This was conducted with BRAKER2 and refined based on functional annotation, repetitive content, and transcriptome alignment. This high-quality genome annotation has 51,419 unique gene models derived from 322,631 initial predictions. Overall, our informatics approach provides a new reference Douglas-fir transcriptome assembly and genome annotation with considerably improved completeness and functional annotation.

Response of photosynthesis, the xanthophyll cycle, and wax in Japanese yew (Taxus cuspidata L.) seedlings and saplings under high light conditions

In order to understand the adaptative changes of the Japanese yew (Taxus cuspidate L.) to high light conditions, this study investigated gas-exchange, chlorophyll fluorescence, chlorophyll, and the impact of epicuticular wax on the gas-exchange and photoinhibition of Japanese yew seedlings and saplings. The chlorophyll content per unit area and photosynthetic rate in seedling leaves were significantly lower than in sapling leaves. When leaves from seedlings and saplings were exposed to 1,200 μmol·m^-2·s^-1 photon flux density (PFD) for 2 h, seedling leaves exhibited a greater down-regulation of maximum quantum yield (Fv/Fm) and actual photosystem II efficiency ( Φ PSII). Non-photochemical quenching (NPQ) and high energy quenching (qE) in sapling leaves were much higher than in seedling leaves when both were exposed to 1,200 μmol·m^-2·s^-1 PFD for 2 h. At a low level of O₂, the photorespiration rate (P_r) and the ratio of photorespiration/gross photosynthetic rate (P_r/P_g) in seedling leaves were lower than in sapling leaves when both were exposed to 1,200 μmol·m^-2·s^-1 PFD, but this difference did not reach statistical significance (P < 0.05). Compared with sapling leaves, seedling leaves exhibited lower levels of xanthophyll pool. Epicuticular wax content on seedling leaves was significantly lower than on sapling leaves. The results of this study showed that wax coverage on the leaf surface decreased the photosynthetic rate in sapling leaves as a consequence of decreased stomatal conductance. Epicuticular wax is related to tree age and photoinhibition prevention in the Japanese yew. It is possible that lower photosynthetic rate, lower NPQ depending on the xanthophyll cycle, and lower deposition of epicuticular wax results in seedling plants that are not adapted to high light conditions.

Transcriptome analysis provides insights into light condition effect on paclitaxel biosynthesis in yew saplings

BACKGROUND

Taxus is a rare gymnosperm plant that is the sole producer of the anticancer drug paclitaxel. The growth and development of Taxus is affected by environmental factors such as light. However, little is known about how light conditions affect growth and metabolic processes, especially paclitaxel biosynthesis.

RESULTS

In this study, we applied three different light conditions to Taxus chinensis young saplings and investigated the physiological response and gene expression. Our observations showed that exposure to high light led to oxidative stress, caused photoinhibition, and damaged the photosynthetic systems in T. chinensis. The paclitaxel content in T. chinensis leaves was significantly decreased after the light intensity increased. Transcriptomic analysis revealed that numerous genes involved in paclitaxel biosynthesis and phenylpropanoid metabolic pathways were downregulated under high light. We also analyzed the expression of JA signaling genes, bHLH, MYB, AP2/ERF transcription factors, and the CYP450 families that are potentially related to paclitaxel biosynthesis. We found that several CYP450s, MYB and AP2/ERF genes were induced by high light. These genes may play an important role in tolerance to excessive light or heat stress in T. chinensis.

CONCLUSIONS

Our study elucidates the molecular mechanism of the effects of light conditions on the growth and development of T. chinensis and paclitaxel biosynthesis, thus facilitating the artificial regeneration of Taxus and enhancing paclitaxel production.

Full-length fruit transcriptomes of southern highbush (Vaccinium sp.) and rabbiteye (V. virgatum Ait.) blueberry

Background

Blueberries (Vaccinium sp.) are native to North America and breeding efforts to improve blueberry fruit quality are focused on improving traits such as increased firmness, enhanced flavor and greater shelf-life. Such efforts require additional genomic resources, especially in southern highbush and rabbiteye blueberries.

Results

We generated the first full-length fruit transcriptome for the southern highbush and rabbiteye blueberry using the cultivars, Suziblue and Powderblue, respectively. The transcriptome was generated using the Pacific Biosciences single-molecule long-read isoform sequencing platform with cDNA pooled from seven stages during fruit development and postharvest storage. Raw reads were processed through the Isoseq pipeline and full-length transcripts were mapped to the ‘Draper’ genome with unmapped reads collapsed using Cogent. Finally, we identified 16,299 and 15,882 non-redundant transcripts in ‘Suziblue’ and ‘Powderblue’ respectively by combining the reads mapped to Northern Highbush blueberry ‘Draper’ genome and Cogent analysis. In both cultivars, > 80% of sequences were longer than 1,000 nt, with the median transcript length around 1,700 nt. Functionally annotated transcripts using Blast2GO were > 92% in both ‘Suziblue’ and ‘Powderblue’ with overall equal distribution of gene ontology (GO) terms in the two cultivars. Analyses of alternative splicing events indicated that around 40% non-redundant sequences exhibited more than one isoform. Additionally, long non-coding RNAs were predicted to represent 5.6% and 7% of the transcriptomes in ‘Suziblue’ and ‘Powderblue’, respectively. Fruit ripening is regulated by several hormone-related genes and transcription factors. Among transcripts associated with phytohormone metabolism/signaling, the highest number of transcripts were related to abscisic acid (ABA) and auxin metabolism followed by those for brassinosteroid, jasmonic acid and ethylene metabolism. Among transcription factor-associated transcripts, those belonging to ripening-related APETALA2/ethylene-responsive element-binding factor (AP2/ERF), NAC (NAM, ATAF1/2 and CUC2), leucine zipper (HB-zip), basic helix-loop-helix (bHLH), MYB (v-MYB, discovered in avian myeloblastosis virus genome) and MADS-Box gene families, were abundant.

Further we measured three fruit ripening quality traits and indicators [ABA, and anthocyanin concentration, and texture] during fruit development and ripening. ABA concentration increased during the initial stages of fruit ripening and then declined at the Ripe stage, whereas anthocyanin content increased during the final stages of fruit ripening in both cultivars. Fruit firmness declined during ripening in ‘Powderblue’. Genes associated with the above parameters were identified using the full-length transcriptome. Transcript abundance patterns of these genes were consistent with changes in the fruit ripening and quality-related characteristics.

Conclusions

A full-length, well-annotated fruit transcriptome was generated for two blueberry species commonly cultivated in the southeastern United States. The robustness of the transcriptome was verified by the identification and expression analyses of multiple fruit ripening and quality–regulating genes. The full-length transcriptome is a valuable addition to the blueberry genomic resources and will aid in further improving the annotation. It will also provide a useful resource for the investigation of molecular aspects of ripening and postharvest processes.

Comprehensive collection of genes and comparative analysis of full-length transcriptome sequences from Japanese larch (Larix kaempferi) and Kuril larch (Larix gmelinii var. japonica)

BACKGROUND

Japanese larch (Larix kaempferi) is an economically important deciduous conifer species that grows in cool-temperate forests and is endemic to Japan. Kuril larch (L. gmelinii var. japonica) is a variety of Dahurian larch that is naturally distributed in the Kuril Islands and Sakhalin. The hybrid larch (L. gmelinii var. japonica × L. kaempferi) exhibits heterosis, which manifests as rapid juvenile growth and high resistance to vole grazing. Since these superior characteristics have been valued by forestry managers, the hybrid larch is one of the most important plantation species in Hokkaido. To accelerate molecular breeding in these species, we collected and compared full-length cDNA isoforms (Iso-Seq) and RNA-Seq short-read, and merged them to construct candidate gene as reference for both Larix species. To validate the results, candidate protein-coding genes (ORFs) related to some flowering signal-related genes ​were screened from the reference sequences, and the phylogenetic relationship with closely related species was elucidated.

RESULTS

Using the isoform sequencing of PacBio RS ll and the de novo assembly of RNA-Seq short-read sequences, we identified 50,690 and 38,684 ORFs in Japanese larch and Kuril larch, respectively. BUSCO completeness values were 90.5% and 92.1% in the Japanese and Kuril larches, respectively. After comparing the collected ORFs from the two larch species, a total of 19,813 clusters, comprising 22,571 Japanese larch ORFs and 22,667 Kuril larch ORFs, were contained in the intersection of the Venn diagram. In addition, we screened several ORFs related to flowering signals (SUPPRESSER OF OVEREXPRESSION OF CO1: SOC1, LEAFY: LFY, FLOWERING Locus T: FT, CONSTANCE: CO) from both reference sequences, and very similar found in other species.

CONCLUSIONS

The collected ORFs will be useful as reference sequences for molecular breeding of Japanese and Kuril larches, and also for clarifying the evolution of the conifer genome and investigating functional genomics.

Integrated SMRT and Illumina Sequencing Provide New Insights into Crocin Biosynthesis of Gardenia jasminoides

Crocins are valuable bioactive components of gardenia fruit, and their biosynthesis and accumulation have attracted widespread interest. Studies have investigated the biosynthesis and accumulation of crocin based on Illumina sequencing, but there is a lack of reports based on full-length transcriptome sequencing. Utilising SMRT sequencing and high-performance liquid chromatography (HPLC), we explored crocin biosynthesis and accumulation in the fruit of Gardenia jasminoides. HPLC analysis showed that crocins specifically exist in fruit and that the content of crocins increases gradually during fruit development. SMRT sequencing generated 46,715 high-quality full-length isoforms, including 5230 novel isoforms that are not present in the G. jasminoides genome. Furthermore, a total of 46 genes and 91 lncRNAs were involved in the biosynthesis and accumulation of crocin. The qRT-PCR indicated that genes involved in crocin biosynthesis reached a peak in the NOV stage. These findings contributed to our understanding of crocin biosynthesis and accumulation.

Endophytic Fungi: Key Insights, Emerging Prospects, and Challenges in Natural Product Drug Discovery

Plant-associated endophytes define an important symbiotic association in nature and are established bio-reservoirs of plant-derived natural products. Endophytes colonize the internal tissues of a plant without causing any disease symptoms or apparent changes. Recently, there has been a growing interest in endophytes because of their beneficial effects on the production of novel metabolites of pharmacological significance. Studies have highlighted the socio-economic implications of endophytic fungi in agriculture, medicine, and the environment, with considerable success. Endophytic fungi-mediated biosynthesis of well-known metabolites includes taxol from Taxomyces andreanae, azadirachtin A and B from Eupenicillium parvum, vincristine from Fusarium oxysporum, and quinine from Phomopsis sp. The discovery of the billion-dollar anticancer drug taxol was a landmark in endophyte biology/research and established new paradigms for the metabolic potential of plant-associated endophytes. In addition, endophytic fungi have emerged as potential prolific producers of antimicrobials, antiseptics, and antibiotics of plant origin. Although extensively studied as a “production platform” of novel pharmacological metabolites, the molecular mechanisms of plant–endophyte dynamics remain less understood/explored for their efficient utilization in drug discovery. The emerging trends in endophytic fungi-mediated biosynthesis of novel bioactive metabolites, success stories of key pharmacological metabolites, strategies to overcome the existing challenges in endophyte biology, and future direction in endophytic fungi-based drug discovery forms the underlying theme of this article.

Long-read transcriptome sequencing provides insight into lignan biosynthesis during fruit development in Schisandra chinensis

BACKGROUND

Schisandra chinensis, an ancient member of the most basal angiosperm lineage which is known as the ANITA, is a fruit-bearing vine with the pharmacological effects of a multidrug system, such as antioxidant, anti-inflammatory, cardioprotective, neuroprotective, anti-osteoporosis effects. Its major bioactive compound is represented by lignans such as schisandrin. Molecular characterization of lignan biosynthesis in S. chinensis is of great importance for improving the production of this class of active compound. However, the biosynthetic mechanism of schisandrin remains largely unknown.

RESULTS

To understand the potential key catalytic steps and their regulation of schisandrin biosynthesis, we generated genome-wide transcriptome data from three different tissues of S. chinensis cultivar Cheongsoon, including leaf, root, and fruit, via long- and short-read sequencing technologies. A total of 132,856 assembled transcripts were generated with an average length of 1.9 kb and high assembly completeness. Overall, our data presented effective, accurate gene annotation in the prediction of functional pathways. In particular, the annotation revealed the abundance of transcripts related to phenylpropanoid biosynthesis. Remarkably, transcriptome profiling during fruit development of S. chinensis cultivar Cheongsoon revealed that the phenylpropanoid biosynthetic pathway, specific to coniferyl alcohol biosynthesis, showed a tendency to be upregulated at the postfruit development stage. Further the analysis also revealed that the pathway forms a transcriptional network with fruit ripening-related genes, especially the ABA signaling-related pathway. Finally, candidate unigenes homologous to isoeugenol synthase 1 (IGS1) and dirigent-like protein (DIR), which are subsequently activated by phenylpropanoid biosynthesis and thus catalyze key upstream steps in schisandrin biosynthesis, were identified. Their expression was increased at the postfruit development stage, suggesting that they may be involved in the regulation of schisandrin biosynthesis in S. chinensis.

CONCLUSIONS

Our results provide new insights into the production and accumulation of schisandrin in S. chinensis berries and will be utilized as a valuable transcriptomic resource for improving the schisandrin content.

Role of female-predominant MYB39-bHLH13 complex in sexually dimorphic accumulation of taxol in Taxus media

Taxus trees are major natural sources for the extraction of taxol, an anti-cancer agent used worldwide. Taxus media is a dioecious woody tree with high taxol yield. However, the sexually dimorphic accumulation of taxoids in T. media is largely unknown. Our study revealed high accumulation of taxoids in female T. media trees using a UPLC-MS/MS method. Thereafter, many differential metabolites and genes between female and male T. media trees were identified using metabolomic and transcriptomic analyses, respectively. Most of the taxol-related genes were predominantly expressed in female trees. A female-specific R2R3-MYB transcription factor gene, TmMYB39, was identified. Furthermore, bimolecular fluorescence complementation and yeast two-hybrid assays suggested the potential interaction between TmMYB39 and TmbHLH13. Several taxol biosynthesis-related promoter sequences were isolated and used for the screening of MYB recognition elements. The electrophoretic mobility shift assay indicated that TmMYB39 could bind to the promoters of the GGPPS, T10OH, T13OH, and TBT genes. Interaction between TmMYB39 and TmbHLH13 transactivated the expression of the GGPPS and T10OH genes. TmMYB39 might function in the transcriptional regulation of taxol biosynthesis through an MYB-bHLH module. Our results give a potential explanation for the sexually dimorphic biosynthesis of taxol in T. media.

Taxus yunnanensis genome offers insights into gymnosperm phylogeny and taxol production

Taxol, a natural product derived from Taxus, is one of the most effective natural anticancer drugs and the biosynthetic pathway of Taxol is the basis of heterologous bio-production. Here, we report a high-quality genome assembly and annotation of Taxus yunnanensis based on 10.7 Gb sequences assembled into 12 chromosomes with contig N50 and scaffold N50 of 2.89 Mb and 966.80 Mb, respectively. Phylogenomic analyses show that T. yunnanensis is most closely related to Sequoiadendron giganteum among the sampled taxa, with an estimated divergence time of 133.4-213.0 MYA. As with most gymnosperms, and unlike most angiosperms, there is no evidence of a recent whole-genome duplication in T. yunnanensis. Repetitive sequences, especially long terminal repeat retrotransposons, are prevalent in the T. yunnanensis genome, contributing to its large genome size. We further integrated genomic and transcriptomic data to unveil clusters of genes involved in Taxol synthesis, located on the chromosome 12, while gene families encoding hydroxylase in the Taxol pathway exhibited significant expansion. Our study contributes to the further elucidation of gymnosperm relationships and the Taxol biosynthetic pathway.

Optimization of Taxol Extraction Process Using Response Surface Methodology and Investigation of Temporal and Spatial Distribution of Taxol in Taxus mairei

Taxus mairei is an important source for industrial extraction of taxol in China. However, the standard and steps of extraction are currently not uniform, which seriously affects the taxol yield. In the present study, the influence of four factors (methanol concentration, solid-liquid ratio, ultrasonic extraction temperature, and ultrasonic extraction time) on the taxol yield was successively explored in T. mairei. A response surface methodology (RSM) was used to optimize the extraction process based on the single-factor experiments above. The optimal conditions were as follows: methanol concentration was 90%, solid-liquid ratio was 1:15 (g/mL), ultrasonic extraction temperature was 40 °C and ultrasonic extraction time was 60 min. Moreover, the twigs and needles from T. mairei with different tree ages were treated by the optimum extraction process, which further revealed temporal and spatial distribution of taxol in the reproducible tissues. Interestingly, the taxol content was relatively higher in needles of T. ‘Jinxishan’ (a cultivar from T. mairei with yellow aril, FY), but was less in FY twigs. The accumulation of taxol in twigs and leaves of females (with red aril, FR) was significantly higher than that of males (M); however, the content showed a decreasing trend with the increasing tree ages. Therefore, it is suitable to increase the proportion of female trees especially the FY leaves as raw materials for the industrial production of taxol from T. mairei, and the tree ages should be better controlled at 3–7 years.

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

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

The Taxus genome provides insights into paclitaxel biosynthesis

The ancient gymnosperm genus Taxus is the exclusive source of the anticancer drug paclitaxel, yet no reference genome sequences are available for comprehensively elucidating the paclitaxel biosynthesis pathway. We have completed a chromosome-level genome of Taxus chinensis var. mairei with a total length of 10.23 gigabases. Taxus shared an ancestral whole-genome duplication with the coniferophyte lineage and underwent distinct transposon evolution. We discovered a unique physical and functional grouping of CYP725As (cytochrome P450) in the Taxus genome for paclitaxel biosynthesis. We also identified a gene cluster for taxadiene biosynthesis, which was formed mainly by gene duplications. This study will facilitate the elucidation of paclitaxel biosynthesis and unleash the biotechnological potential of Taxus.

The Research Progress of Taxol in Taxus

BACKGROUND

Taxus is a valuable woody species with important medicinal value. The bark of Taxus can produce taxol, a natural antineoplastic drug that is widely used in the treatment of breast, ovarian and lung cancers. However, the low content of taxol in the bark of Taxus can not meet the growing clinical demands, so the current research aims at finding ways to increase taxol production.

OBJECTIVE

In this review, the research progress of taxol including the factors affecting the taxol content, biosynthesis pathway of taxol, production of taxol in vitro and the application of multi-omics approaches in Taxus as well as future research prospects will be discussed.

RESULTS

The taxol content is not only dependent on the species, age and tissues but is also affected by light, moisture levels, temperature, soil fertility and microbes. Most of the enzymes in the taxol biosynthesis pathway have been identified and characterized. Total chemical synthesis, semi-synthesis, plant cell culture and biosynthesis in endophytic fungi have been explored to product taxol. Multi-omics have been used to study Taxus and taxol.

CONCLUSION

Further efforts in the identification of unknown enzymes in the taxol biosynthesis pathway, establishment of the genetic transformation system in Taxus and the regulatory mechanism of taxol biosynthesis and Taxus cell growth will play a significant role in improving the yield of taxol in Taxus cells and plants.

Recent Research Progress in Taxol Biosynthetic Pathway and Acylation Reactions Mediated by Taxus Acyltransferases

Taxol is one of the most effective anticancer drugs in the world that is widely used in the treatments of breast, lung and ovarian cancer. The elucidation of the taxol biosynthetic pathway is the key to solve the problem of taxol supply. So far, the taxol biosynthetic pathway has been reported to require an estimated 20 steps of enzymatic reactions, and sixteen enzymes involved in the taxol pathway have been well characterized, including a novel taxane-10β-hydroxylase (T10βOH) and a newly putative β-phenylalanyl-CoA ligase (PCL). Moreover, the source and formation of the taxane core and the details of the downstream synthetic pathway have been basically depicted, while the modification of the core taxane skeleton has not been fully reported, mainly concerning the developments from diol intermediates to 2-debenzoyltaxane. The acylation reaction mediated by specialized Taxus BAHD family acyltransferases (ACTs) is recognized as one of the most important steps in the modification of core taxane skeleton that contribute to the increase of taxol yield. Recently, the influence of acylation on the functional and structural diversity of taxanes has also been continuously revealed. This review summarizes the latest research advances of the taxol biosynthetic pathway and systematically discusses the acylation reactions supported by Taxus ACTs. The underlying mechanism could improve the understanding of taxol biosynthesis, and provide a theoretical basis for the mass production of taxol.

Integration of early disease-resistance phenotyping, histological characterization, and transcriptome sequencing reveals insights into downy mildew resistance in impatiens

Downy mildew (DM), caused by obligate parasitic oomycetes, is a destructive disease for a wide range of crops worldwide. Recent outbreaks of impatiens downy mildew (IDM) in many countries have caused huge economic losses. A system to reveal plant-pathogen interactions in the early stage of infection and quickly assess resistance/susceptibility of plants to DM is desired. In this study, we established an early and rapid system to achieve these goals using impatiens as a model. Thirty-two cultivars of Impatiens walleriana and I. hawkeri were evaluated for their responses to IDM at cotyledon, first/second pair of true leaf, and mature plant stages. All I. walleriana cultivars were highly susceptible to IDM. While all I. hawkeri cultivars were resistant to IDM starting at the first true leaf stage, many (14/16) were susceptible to IDM at the cotyledon stage. Two cultivars showed resistance even at the cotyledon stage. Histological characterization showed that the resistance mechanism of the I. hawkeri cultivars resembles that in grapevine and type II resistance in sunflower. By integrating full-length transcriptome sequencing (Iso-Seq) and RNA-Seq, we constructed the first reference transcriptome for Impatiens comprised of 48,758 sequences with an N50 length of 2060 bp. Comparative transcriptome and qRT-PCR analyses revealed strong candidate genes for IDM resistance, including three resistance genes orthologous to the sunflower gene RGC203, a potential candidate associated with DM resistance. Our approach of integrating early disease-resistance phenotyping, histological characterization, and transcriptome analysis lay a solid foundation to improve DM resistance in impatiens and may provide a model for other crops.

Full-length SMRT transcriptome sequencing and microsatellite characterization in Paulownia catalpifolia

Paulownia catalpifolia is an important, fast-growing timber species known for its high density, color and texture. However, few transcriptomic and genetic studies have been conducted in P. catalpifolia. In this study, single-molecule real-time sequencing technology was applied to obtain the full-length transcriptome of P. catalpifolia leaves treated with varying degrees of drought stress. The sequencing data were then used to search for microsatellites, or simple sequence repeats (SSRs). A total of 28.83 Gb data were generated, 25,969 high-quality (HQ) transcripts with an average length of 1624 bp were acquired after removing the redundant reads, and 25,602 HQ transcripts (98.59%) were annotated using public databases. Among the HQ transcripts, 16,722 intact coding sequences, 149 long non-coding RNAs and 179 alternative splicing events were predicted, respectively. A total of 7367 SSR loci were distributed throughout 6293 HQ transcripts, of which 763 complex SSRs and 6604 complete SSRs. The SSR appearance frequency was 28.37%, and the average distribution distance was 5.59 kb. Among the 6604 complete SSR loci, 1-3 nucleotide repeats were dominant, occupying 97.85% of the total SSR loci, of which mono-, di- and tri-nucleotide repeats were 44.68%, 33.86% and 19.31%, respectively. We detected 112 repeat motifs, of which A/T (42.64%), AG/CT (12.22%), GA/TC (9.63%), GAA/TTC (1.57%) and CCA/TGG (1.54%) were most common in mono-, di- and tri-nucleotide repeats, respectively. The length of the repeat SSR motifs was 10-88 bp, and 4997 (75.67%) were ≤ 20 bp. This study provides a novel full-length transcriptome reference for P. catalpifolia and will facilitate the identification of germplasm resources and breeding of new drought-resistant P. catalpifolia varieties.

Deep learning approaches for natural product discovery from plant endophytic microbiomes

Plant microbiomes are not only diverse, but also appear to host a vast pool of secondary metabolites holding great promise for bioactive natural products and drug discovery. Yet, most microbes within plants appear to be uncultivable, and for those that can be cultivated, their metabolic potential lies largely hidden through regulatory silencing of biosynthetic genes. The recent explosion of powerful interdisciplinary approaches, including multi-omics methods to address multi-trophic interactions and artificial intelligence-based computational approaches to infer distribution of function, together present a paradigm shift in high-throughput approaches to natural product discovery from plant-associated microbes. Arguably, the key to characterizing and harnessing this biochemical capacity depends on a novel, systematic approach to characterize the triggers that turn on secondary metabolite biosynthesis through molecular or genetic signals from the host plant, members of the rich 'in planta' community, or from the environment. This review explores breakthrough approaches for natural product discovery from plant microbiomes, emphasizing the promise of deep learning as a tool for endophyte bioprospecting, endophyte biochemical novelty prediction, and endophyte regulatory control. It concludes with a proposed pipeline to harness global databases (genomic, metabolomic, regulomic, and chemical) to uncover and unsilence desirable natural products.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1186/s40793-021-00375-0.

Omic analysis of the endangered Taxaceae species Pseudotaxus chienii revealed the differences in taxol biosynthesis pathway between Pseudotaxus and Taxus yunnanensis trees

BACKGROUND

Taxol is an efficient anticancer drug accumulated in Taxus species. Pseudotaxus chienii is an important member of Taxaceae, however, the level of six taxoids in P. chienii is largely unknown.

RESULTS

High accumulation of 10-DAB, taxol, and 7-E-PTX suggested that P. chienii is a good taxol-yielding species for large-scale cultivation. By the omics approaches, a total of 3,387 metabolites and 61,146 unigenes were detected and annotated. Compared with a representative Taxus tree (Taxus yunnanensis), most of the differentially accumulated metabolites and differential expressed genes were assigned into 10 primary and secondary metabolism pathways. Comparative analyses revealed the variations in the precursors and intermediate products of taxol biosynthesis between P. chienii and T. yunnanensis. Taxusin-like metabolites highly accumulated in P. chienii, suggesting a wider value of P. chienii in pharmaceutical industry.

CONCLUSIONS

In our study, the occurrence of taxoids in P. chienii was determined. The differential expression of key genes involved in the taxol biosynthesis pathway is the major cause of the differential accumulation of taxoids. Moreover, identification of a number of differentially expressed transcription factors provided more candidate regulators of taxol biosynthesis. Our study may help to reveal the differences between Pseudotaxus and Taxus trees, and promote resource utilization of the endangered and rarely studied P. chienii.

Recent Advances in Metabolic Engineering, Protein Engineering, and Transcriptome-Guided Insights Toward Synthetic Production of Taxol

The diterpenoid paclitaxel (Taxol®) is a blockbuster anticancer agent that was originally isolated from the Pacific yew (Taxus brevifolia) five decades ago. Despite the wealth of information gained over the years on Taxol research, there still remains supply issues to meet increasing clinical demand. Although alternative Taxol production methods have been developed, they still face several drawbacks that cause supply shortages and high production costs. It is highly desired to develop biotechnological production platforms for Taxol, however, there are still gaps in our understanding of the biosynthetic pathway, catalytic enzymes, regulatory and control mechanisms that hamper production of this critical drug by synthetic biology approaches. Over the past 5 years, significant advances were made in metabolic engineering and optimization of the Taxol pathway in different hosts, leading to accumulation of taxane intermediates. Computational and experimental approaches were leveraged to gain mechanistic insights into the catalytic cycle of pathway enzymes and guide rational protein engineering efforts to improve catalytic fitness and substrate/product specificity, especially of the cytochrome P450s (CYP450s). Notable breakthroughs were also realized in engineering the pathway in plant hosts that are more promising in addressing the challenging CYP450 chemistry. Here, we review these recent advances and in addition, we summarize recent transcriptomic data sets of Taxus species and elicited culture cells, and give a bird's-eye view of the information that can be gleaned from these publicly available resources. Recent mining of transcriptome data sets led to discovery of two putative pathway enzymes, provided many lead candidates for the missing steps and provided new insights on the regulatory mechanisms governing Taxol biosynthesis. All these inferences are relevant to future biotechnological production of Taxol.

Full-Length Transcriptome Analysis of Four Different Tissues of Cephalotaxus oliveri

Cephalotaxus oliveri is a tertiary relict conifer endemic to China, regarded as a national second-level protected plant in China. This species has experienced severe changes in temperature and precipitation in the past millions of years, adapting well to harsh environments. In view of global climate change and its endangered conditions, it is crucial to study how it responds to changes in temperature and precipitation for its conservation work. In this study, single-molecule real-time (SMRT) sequencing and Illumina RNA sequencing were combined to generate the complete transcriptome of C. oliveri. Using the RNA-seq data to correct the SMRT sequencing data, the four tissues obtained 63,831 (root), 58,108 (stem), 33,013 (leaf) and 62,436 (male cone) full-length unigenes, with a N50 length of 2523, 3480, 3181, and 3267 bp, respectively. Additionally, 35,887, 11,306, 36,422, and 25,439 SSRs were detected for the male cone, leaf, root, and stem, respectively. The number of long non-coding RNAs predicted from the root was the largest (11,113), and the other tissues were 3408 (stem), 3193 (leaf), and 3107 (male cone), respectively. Functional annotation and enrichment analysis of tissue-specific expressed genes revealed the special roles in response to environmental stress and adaptability in the different four tissues. We also characterized the gene families and pathways related to abiotic factors. This work provides a comprehensive transcriptome resource for C. oliveri, and this resource will facilitate further studies on the functional genomics and adaptive evolution of C. oliveri.

Efficient Biosynthesis of (2S)-Eriodictyol from (2S)-Naringenin in Saccharomyces cerevisiae through a Combination of Promoter Adjustment and Directed Evolution

The compound (2S)-eriodictyol is an important flavonoid that can be derived from (2S)-naringenin through flavonoid 3'-hydroxylase (F3'H) catalyzation. F3'H is a cytochrome P450 enzyme that requires a cytochrome P450 reductase (CPR) to function. However, P450s have limited applications in industrial scale biosynthesis, owing to their low activity. Here, an efficient SmF3'H and a matched SmCPR were identified from Silybum marianum. To improve the efficiency of SmF3'H, we established a high-throughput detection method for (2S)-eriodictyol, in which the promoter combination of SmF3'H and SmCPR were optimized in Saccharomyces cerevisiae. The results revealed that SmF3'H/SmCPR should be expressed by using promoters with similar and strong expression levels. Furthermore, directed evolution was applied to further improve the efficiency of SmF3'H/SmCPR. With the optimized promoter and mutated combinations SmF3'HD285N/SmCPRI453V, the (2S)-eriodictyol titer was improved to 3.3 g/L, the highest titer in currently available reports. These results indicated that S. cerevisiae is an ideal platform for functional expression of flavonoid related P450 enzymes.

Full-length transcriptome sequencing analysis and development of EST-SSR markers for the endangered species Populus wulianensis

Populus wulianensis is an endangered species endemic to Shandong Province, China. Despite the economic and ornamental value of this species, few genomics and genetic studies have been performed. In this study, we performed a relevant analysis of the full-length transcriptome sequencing data of P. wulianensis and obtained expressed sequence tag (EST)-simple sequence repeat (SSR) markers with polymorphisms that can be used for further genetic research. In total, 8.18 Gb (3,521,665) clean reads with an average GC content of 42.12% were obtained. From the corrected 64,737 high-quality isoforms, 42,323 transcript sequences were obtained after redundancy analysis with CD-HIT. Among these transcript sequences, 41,876 sequences were annotated successfully. A total of 23,539 potential EST-SSRs were identified from 16,057 sequences. Excluding mononucleotides, the most abundant motifs were trinucleotide SSRs (47.80%), followed by di- (46.80%), tetra- (2.98%), hexa- (1.58%) and pentanucleotide SSRs (0.84%). Among the 100 designed EST-SSRs, 18 were polymorphic with high PIC values (0.721 and 0.683) and could be used for analyses of the genetic diversity and population structure of P. wulianensis. These full-length transcriptome sequencing data will facilitate gene discovery and functional genomics research in P. wulianensis, and the novel EST-SSRs developed in our study will promote molecular-assisted breeding, genetic diversity and conservation biology research in this species.

Full-length sequencing of ginkgo transcriptomes for an in-depth understanding of flavonoid and terpenoid trilactone biosynthesis

Ginkgo biloba L. is regarded as the most ancient living tree, and its kernel has been used as a traditional Chinese medicine for more than 2,000 years. The leaf extracts of this tree have been among the bestselling herbal remedies in Western countries since the last century. To understand the biosynthesis of the pharmacologically active ingredients in G. biloba, flavonoids and terpenoid trilactones (TTLs), we sequenced the transcriptomes of G. biloba leaves, kernels and testae with Iso-Seq and RNA-Seq technologies and obtained 152,524 clean consensus reads. When these reads were used to improve the annotation of the G. biloba genome, 4,856 novel genes, 25,583 new isoforms of previously annotated genes and 4,363 lncRNAs were discovered. Gene ontology and Kyoto Encyclopedia of Genes and Genomes analyses indicated that genes involved in growth, regulation and response to stress were more likely to be regulated by alternative splicing (AS) or alternative polyadenylation (APA), which represent the two most important posttranscriptional regulation mechanisms. It was found that some of the characterized genes involved in the biosynthesis of flavonoids and TTLs were also possibly regulated by AS and APA. Using phylogenetic and gene expression pattern analyses, some candidate genes for the biosynthesis of flavonoids and TTLs were screened. After qRT-PCR validation, the final candidate genes for flavonoid biosynthesis included three UDP-glycosyltransferases and one MYB transcription factor, while the candidate genes for TTL biosynthesis included two cytochrome P450 and one WRKY transcription factor. Our study suggested that Iso-Seq may play an important role in improving genome annotation, elucidating AS and APA mechanisms and discovering candidate genes involved in the biosynthesis of some secondary metabolites.

Tissue-specific study across the stem of Taxus media identifies a phloem-specific TmMYB3 involved in the transcriptional regulation of paclitaxel biosynthesis

Taxus stem barks can be used for extraction of paclitaxel. However, the composition of taxoids across the whole stem and the stem tissue-specificity of paclitaxel biosynthesis-related enzymes remain largely unknown. We used cultivated Taxus media trees for analyses of the chemical composition and protein of major stem tissues by an integrated metabolomic and proteomic approach, and the role of TmMYB3 in paclitaxel biosynthesis was investigated. The metabolomic landscape analysis showed differences in stem tissue-specific accumulation of metabolites. Phytochemical analysis revealed that there is high accumulation of paclitaxel in the phloem. Ten key enzymes involved in paclitaxel biosynthesis were identified, most of which are predominantly produced in the phloem. The full-length sequence of TmMYB3 and partial promoter sequences of five paclitaxel biosynthesis-related genes were isolated. Several MYB recognition elements were found in the promoters of TBT, DBTNBT and TS. Further in vitro and in vivo investigations indicated that TmMYB3 is involved in paclitaxel biosynthesis by activating the expression of TBT and TS. Differences in the taxoid composition of different stem tissues suggest that the whole stem of T. media has potential for biotechnological applications. Phloem-specific TmMYB3 plays a role in the transcriptional regulation of paclitaxel biosynthesis, and may explain the phloem-specific accumulation of paclitaxel.

Characterization and Analysis of the Full-Length Transcriptomes of Multiple Organs in Pseudotaxus chienii (W.C.Cheng) W.C.Cheng

Pseudotaxus chienii, a rare tertiary relict species with economic and ecological value, is a representative of the monotypic genus Pseudotaxus that is endemic to China. P. chienii can adapt well to habitat isolation and ecological heterogeneity under a variety of climate and soil conditions, and is able to survive in harsh environments. However, little is known about the molecular and genetic resources of this long-lived conifer. Herein, we sequenced the transcriptomes of four organs of P. chienii using the PacBio Isoform Sequencing and Illumina RNA Sequencing platforms. Based on the PacBio Iso-Seq data, we obtained 44,896, 58,082, 50,485, and 67,638 full-length unigenes from the root, stem, leaf, and strobilus, respectively, with a mean length of 2692 bp, and a mean N50 length of 3010.75 bp. We then comprehensively annotated these unigenes. The number of organ-specific expressed unigenes ranged from 4393 in leaf to 9124 in strobilus, suggesting their special roles in physiological processes, organ development, and adaptability in the different four organs. A total of 16,562 differentially expressed genes (DEGs) were identified among the four organs and clustered into six subclusters. The gene families related to biotic/abiotic factors, including the TPS, CYP450, and HSP families, were characterized. The expression levels of most DEGs in the phenylpropanoid biosynthesis pathway and plant–pathogen interactions were higher in the root than in the three other organs, suggesting that root constitutes the main organ of defensive compound synthesis and accumulation and has a stronger ability to respond to stress. The sequences were analyzed to predict transcription factors, long non-coding RNAs, and alternative splicing events. The expression levels of most DEGs of C2H2, C3H, bHLH, and bZIP families in the root and stem were higher than those in the leaf and strobilus, indicating that these TFs may play a crucial role in the survival of the root and stem. These results comprise the first comprehensive gene expression profiles obtained for different organs of P. chienii. Our findings will facilitate further studies on the functional genomics, adaptive evolution, and phylogeny of P. chienii, and lay the foundation for the development of conservation strategies for this endangered conifer.

Alternative sources and metabolic engineering of Taxol: Advances and future perspectives

Paclitaxel is one of the strong plant-derived anti-cancer drugs that was first isolated from the Pacific yew. Despite many paclitaxel's clinical successes, the limited accessibility of paclitaxel for clinical trials is recognized as the most important challenge. Thus, researchers are continuously trying to find the innovative ways to meet the community's need for this medicine. In the first step, the alternative sources for Taxol supply were recognized, such as Taxus genus, other plant genera, and endophytic fungi. In the next step, the biosynthetic pathways of Taxol or related metabolites were manipulated in the original organisms, or introduced to heterologous systems and then were manipulated in them. Here, a range of metabolic manipulating approaches have been successfully developed to redirect the metabolic flux toward Taxol, including promoter engineering, enzyme engineering, overexpressing the bottleneck enzymes, over- or down-regulation of transcription factors, activation of the cryptic genes, removing/minimizing the flux for competing pathways, tunable regulation of the metabolic pathway, and increasing the supplies of precursors. In this review, we discuss research progress on the alternative Taxol sources and its metabolic manipulating, and we suggest recent challenges and future perspectives.

IsoSeq transcriptome assembly of C3 panicoid grasses provides tools to study evolutionary change in the Panicoideae

The number of plant species with genomic and transcriptomic data has been increasing rapidly. The grasses-Poaceae-have been well represented among species with published reference genomes. However, as a result the genomes of wild grasses are less frequently targeted by sequencing efforts. Sequence data from wild relatives of crop species in the grasses can aid the study of domestication, gene discovery for breeding and crop improvement, and improve our understanding of the evolution of C4 photosynthesis. Here, we used long-read sequencing technology to characterize the transcriptomes of three C3 panicoid grass species: Dichanthelium oligosanthes, Chasmanthium laxum, and Hymenachne amplexicaulis. Based on alignments to the sorghum genome, we estimate that assembled consensus transcripts from each species capture between 54.2% and 65.7% of the conserved syntenic gene space in grasses. Genes co-opted into C4 were also well represented in this dataset, despite concerns that because these genes might play roles unrelated to photosynthesis in the target species, they would be expressed at low levels and missed by transcript-based sequencing. A combined analysis using syntenic orthologous genes from grasses with published reference genomes and consensus long-read sequences from these wild species was consistent with previously published phylogenies. It is hoped that these data, targeting underrepresented classes of species within the PACMAD grasses-wild species and species utilizing C3 photosynthesis-will aid in future studies of domestication and C4 evolution by decreasing the evolutionary distance between C4 and C3 species within this clade, enabling more accurate comparisons associated with evolution of the C4 pathway.

Comparative metabolomic analysis reveals the variations in taxoids and flavonoids among three Taxus species

BACKGROUND

Trees of the genus Taxus are highly valuable medicinal plants with multiple pharmacological effects on various cancer treatments. Paclitaxel from Taxus trees is an efficient and widely used anticancer drug, however, the accumulation of taxoids and other active ingredients can vary greatly among Taxus species. In our study, the metabolomes of three Taxus species have been investigated.

RESULTS

A total of 2246 metabolites assigned to various primary and secondary metabolic pathways were identified using an untargeted approach. Analysis of differentially accumulated metabolites identified 358 T. media-, 220 T. cuspidata-, and 169 T. mairei-specific accumulated metabolites, respectively. By searching the metabolite pool, 7 MEP pathway precursors, 11 intermediates, side chain products and derivatives of paclitaxel, and paclitaxel itself were detected. Most precursors, initiated intermediates were highly accumulated in T. mairei, and most intermediate products approaching the end point of taxol biosynthesis pathway were primarily accumulated in T. cuspidata and T. media. Our data suggested that there were higher-efficiency pathways to paclitaxel in T. cuspidata and T. media compared with in T. mairei. As an important class of active ingredients in Taxus trees, a majority of flavonoids were predominantly accumulated in T. mairei rather than T. media and T. cuspidata. The variations in several selected taxoids and flavonoids were confirmed using a targeted approach.

CONCLUSIONS

Systematic correlativity analysis identifies a number of metabolites associated with paclitaxel biosynthesis, suggesting a potential negative correlation between flavonoid metabolism and taxoid accumulation. Investigation of the variations in taxoids and other active ingredients will provide us with a deeper understanding of the interspecific differential accumulation of taxoids and an opportunity to accelerate the highest-yielding species breeding and resource utilization.

Hybrid Sequencing of Full-Length cDNA Transcripts of the Medicinal Plant Scutellaria baicalensis

Scutellaria baicalensis is a well-known medicinal plant that produces biologically active flavonoids, such as baicalin, baicalein, and wogonin. Pharmacological studies have shown that these compounds have anti-inflammatory, anti-bacterial, and anti-cancer activities. Therefore, it is of great significance to investigate the genetic information of S. baicalensis, particularly the genes related to the biosynthetic pathways of these compounds. Here, we constructed the full-length transcriptome of S. baicalensis using a hybrid sequencing strategy and acquired 338,136 full-length sequences, accounting for 93.3% of the total reads. After the removal of redundancy and correction with Illumina short reads, 75,785 nonredundant transcripts were generated, among which approximately 98% were annotated with significant hits in the protein databases, and 11,135 sequences were classified as lncRNAs. Differentially expressed gene (DEG) analysis showed that most of the genes related to flavonoid biosynthesis were highly expressed in the roots, consistent with previous reports that the flavonoids were mainly synthesized and accumulated in the roots of S. baicalensis. By constructing unique transcription models, a total of 44,071 alternative splicing (AS) events were identified, with intron retention (IR) accounting for the highest proportion (44.5%). A total of 94 AS events were present in five key genes related to flavonoid biosynthesis, suggesting that AS may play important roles in the regulation of flavonoid biosynthesis in S. baicalensis. This study provided a large number of highly accurate full-length transcripts, which represents a valuable genetic resource for further research of the molecular biology of S. baicalensis, such as the development, breeding, and biosynthesis of active ingredients.