The effects of salicylic acid and glucose on biochemical traits and taxane production in a Taxus baccata callus culture

Transcriptomics and Physiological Analyses Reveal Changes in Paclitaxel Production and Physiological Properties in Taxus cuspidata Suspension Cells in Response to Elicitors

In this research, the cell growth, physiological, and biochemical reactions, as well as the paclitaxel production, of Taxus cuspidata suspension cells after treatment with polyethylene glycol (PEG), cyclodextrin (CD), or salicylic acid (SA) (alone or in combination) were investigated. To reveal the paclitaxel synthesis mechanism of T. cuspidata suspension cells under elicitor treatment, the transcriptomics of the Control group and P + C + S group (PEG + CD + SA) were compared. The results show that there were no significant differences in cell biomass after 5 days of elicitor treatments. However, the content of hydrogen peroxide (H2O2) and malondialdehyde (MDA), and the activities of phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO) after elicitor combination treatments were decreased compared with the single-elicitor treatment. Meanwhile, the antioxidant enzyme activity (superoxide dismutase (SOD), catalase (CAT), and peroxidase (PO)) and the contents of soluble sugar and soluble protein were increased after combination elicitor treatments. Additionally, the paclitaxel yield after treatment with the combination of all three elicitors (P + C + S) was 6.02 times higher than that of the Control group, thus indicating that the combination elicitor treatments had a significant effect on paclitaxel production in T. cuspidata cell suspension culture. Transcriptomics analysis revealed 13,623 differentially expressed genes (DEGs) between the Control and P + C + S treatment groups. Both GO and KEGG analyses showed that the DEGs mainly affected metabolic processes. DEGs associated with antioxidant enzymes, paclitaxel biosynthesis enzymes, and transcription factors were identified. It can be hypothesized that the oxidative stress of suspension cells occurred with elicitor stimulation, thereby leading to a defense response and an up-regulation of the gene expression associated with antioxidant enzymes, paclitaxel synthesis enzymes, and paclitaxel synthesis transcription factors; this ultimately increased the production of paclitaxel.

Targeted control of supporting pathways in paclitaxel biosynthesis with CRISPR-guided methylation

Introduction: Plant cell culture biomanufacturing is rapidly becoming an effective strategy for production of high-value plant natural products, such as therapeutic proteins and small molecules, vaccine adjuvants, and nutraceuticals. Many of these plant natural products are synthesized from diverse molecular building blocks sourced from different metabolic pathways. Even so, engineering approaches for increasing plant natural product biosynthesis have typically focused on the core biosynthetic pathway rather than the supporting pathways. Methods: Here, we use both CRISPR-guided DNA methylation and chemical inhibitors to control flux through the phenylpropanoid pathway in Taxus chinensis, which contributes a phenylalanine derivative to the biosynthesis of paclitaxel (Taxol), a potent anticancer drug. To inhibit PAL, the first committed step in phenylpropanoid biosynthesis, we knocked down expression of PAL in Taxus chinensis plant cell cultures using a CRISPR-guided plant DNA methyltransferase (NtDRM). For chemical inhibition of downstream steps in the pathway, we treated Taxus chinensis plant cell cultures with piperonylic acid and caffeic acid, which inhibit the second and third committed steps in phenylpropanoid biosynthesis: cinnamate 4-hydroxylase (C4H) and 4-coumaroyl-CoA ligase (4CL), respectively. Results: Knockdown of PAL through CRISPR-guided DNA methylation resulted in a profound 25-fold increase in paclitaxel accumulation. Further, through the synergistic action of both chemical inhibitors and precursor feeding of exogenous phenylalanine, we achieve a 3.5-fold increase in paclitaxel biosynthesis and a similar reduction in production of total flavonoids and phenolics. We also observed perturbations to both activity and expression of PAL, illustrating the complex transcriptional co-regulation of these first three pathway steps. Discussion: These results highlight the importance of controlling the metabolic flux of supporting pathways in natural product biosynthesis and pioneers CRISPR-guided methylation as an effective method for metabolic engineering in plant cell cultures. Ultimately, this work demonstrates a powerful method for rewiring plant cell culture systems into next-generation chassis for production of societally valuable compounds.

Mapping quantitative trait loci associated with callus browning in Dongxiang common wild rice (Oryza rufipogon Griff.)

BACKGROUND

Genetic transformation of indica rice (Oryza sativa ssp. indica) is limited by callus browning, which results in poor in vitro tissue culturability. Elucidating the genes in common wild rice (Oryza rufipogon Griff.) that control callus browning is fundamental for improving the tissue culturability of indica rice varieties.

METHODS AND RESULTS

We used a population of 129 O. rufipogon (Dongxiang common wild rice; DXCWR) introgression lines in the elite cultivar GC2 (Oryza sativa ssp. indica) background and 159 simple sequence repeat (SSR) markers to identify quantitative trait loci (QTLs) associated with callus browning. We evaluated callus browning based on the indices of callus browning rate (CBR), callus browning index (CBI), and standard callus browning index (SCBI).

CONCLUSIONS

We detected 30 QTLs associated with callus browning across all lines, mapping to chromosomes 1, 2, 3, 4, 8, 9, and 12. These genomic regions were repeatedly associated with differences in CBR, CBI, and SCBI. The alleles from DXCWR showed additive effects in reducing callus browning. We identified new QTLs near the markers RM247 and RM7003 on chromosome 12, indicating that these QTLs are unique to DXCWR. Furthermore, we identified six introgression lines with significantly lower callus browning. These lines will be useful germplasms for genetic transformation and fine-mapping of the culturability trait.

Salicylic Acid Priming Regulates Stomatal Conductance, Trichome Density and Improves Cadmium Stress Tolerance in Mentha arvensis L

The application of phytohormones through seed priming could enhance quality of important medicinal and aromatic plants (MAPs) under heavy metal stress. We evaluated the potential of salicylic acid (SA) priming for overcoming the adverse effects of cadmium stress in Mentha arvensis L. plants. Suckers of plants were primed with SA before transplanting them into soil. At 30 days after transplanting, two doses (50 and 100 μm) of CdCl₂ were applied to the soil. Both Cd treatments altered plant growth, photosynthetic pigments, leaf gas exchange attributes, and mineral nutrient contents. The 50 and 100 μm Cd treatments increased endogenous Cd content by 97.95 and 98.03%, electrolyte leakage (EL) by 34.21 and 44.38%, hydrogen peroxide (H₂O₂) by 34.71 and 55.80%, malondialdehyde (MDA) by 53.08 and 63.15%, and superoxide content (O₂ ^-•) by 24.07 and 38.43%, respectively. Cd triggered the up-regulation of antioxidant enzyme activities (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; and glutathione reductase GR) and increased osmolyte biosynthesis and, interestingly, secondary metabolite (SM) accumulation. The presence of SA and Cd had an additive effect on these parameters. Nevertheless, plants primed with SA regulated stomatal conductance under Cd stress. SA priming to menthol mint plants under Cd stress overcome the effects of Cd stress while increasing SMs.

Identification of genes associated with biosynthesis of bioactive flavonoids and taxoids in Taxus cuspidata Sieb. et Zucc. plantlets exposed to UV-B radiation

UV-B radiation is a typical environmental stressor that can promote phytochemical accumulation in plants. Taxus species are highly appreciated due to the existence of bioactive taxoids (especially paclitaxel) and flavonoids. However, the effect of UV-B radiation on taxoid and flavonoid biosynthesis in Taxus cuspidata Sieb. et Zucc. is largely unknown. In the present work, the accumulation of taxoids and flavonoids in T. cuspidata plantlets was significantly induced by 12 and 24 h of UV-B radiation (3 W/m²), and a large number of significantly differentially expressed genes were obtained via transcriptomic analysis. The significant up-regulation of antioxidant enzyme- and flavonoid biosynthesis-related genes (phenylalanine ammonia lyase 1, chalcone synthase 2, flavonol synthase 1, and flavonoid 3', 5'-hydroxylase 2), suggested that UV-B might cause the oxidative stress thus promoting flavonoid accumulation in T. cuspidata. Moreover, the expression of some genes related to jasmonate metabolism and taxoid biosynthesis (taxadiene synthase, baccatin III-3-amino 3-phenylpropanoyltransferase 1, taxadiene-5α-hydroxylase, and ethylene response factors 15) was significantly activated, which indicated that UV-B might initiate jasmonate signaling pathway that contributed to taxoid enhancement in T. cuspidata. Additionally, the identification of some up-regulated genes involved in lignin biosynthesis pathway indicated that the lignification process in T. cuspidata might be stimulated for defense against UV-B radiation. Overall, our findings provided a better understanding of some potential key genes associated with flavonoid and taxoid biosynthesis in T. cuspidata exposed to UV-B radiation.

Phyto-factories of anti-cancer compounds: a tissue culture perspective

Background

Cancer is one of the most critical but ubiquitous causes of death grappled from past decades. Widely used chemotherapy with cytotoxic activity blocks/ kills the cancer cell. The compounds targeted for anticancerous activity are either derived synthetically or naturally (through plants or microbial origin). Current day, versatile role of plants in medicinal field has been attributed to the secondary metabolites it produces, known for their anticancer activity. Therefore, discovery, identification and commercial production of such novel anticancer drugs is escalated and are centerpiece for pharmaceuticals.

Main body

A biotechnological approach, principally tissue culture, leads the candidacy to be an alternative method for production of anticancer compounds. A wide range of bioactive agents like alkaloids, steroids, phenolics, saponins, flavonoids, and terpenoids are in huge demand commercially. Plant tissue culture applications are constructively more advantageous over conventional methods in terms of their continuous, controlled, aseptic production, large scale and de novo synthesis opportunity. Various bioreactors are used for mass cultivation of bioactive compound at commercial level. For example: stirred tank reactors are used for production of shikonin from Lithospermum erythrorhizon, vincristine from Catharanthus roseus, podophyllotoxin from Podophyllum etc. Strategies like callus culture, suspension culture and hairy root culture are opted for mass cultivation of these bioactives.

Conclusions

This review summarizes plant tissue culture as a promising strategy proven to be a colossal breakthrough in reliable and continuous production of existing and novel anticancer compounds and help in combating the increasing future demands.

Elicitor-mediated enhancement of biomass, polyphenols, mangiferin production and antioxidant activities in callus cultures of Salacia chinensis L

The present investigation aimed to improve callus biomass, polyphenolic content, biosynthesis of mangiferin and biological potential following application of different elicitor treatments for medicinally important Salacia chinensis L. The leaf-derived callus cultures were established on Murashige and Skoog's (MS) medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D: 2.0 mg/l) and 6-benzylaminopurine (BAP: 1.5 mg/l). These cultures were treated with different elicitors viz. jasmonic acid (JA), methyl jasmonate (MeJA) and yeast extracts (YE). The highest calli biomass (five-fold increase within 4 weeks) was achieved when callus was treated with JA (75 µM). The callus obtained on MS medium supplemented with 2,4-D (2.0 mg/l), BAP (1.5 mg/l) and treated with JA (75 µM) displayed augmented values for total phenolics, flavonoids and mangiferin contents. Besides, same treatment elicits the calli for antioxidant properties as evaluated by 2,2-diphenyl-2-picrylhydrazyl (DPPH), ferric-reducing antioxidant power (FRAP) and metal chelating assays. This is the first report on the elicitation study in genus Salacia and, therefore, the discoveries suggested that, S. chinensis calli might be a perfect source for large-scale production of industrially important secondary metabolites. Concurrently data provide accumulated information demonstrating its prominent antioxidant effect revealing its potential without disturbing natural resources.

Effect of methyl jasmonate and salicylic acid on the production of metabolites in cell suspensions cultures of Piper cumanense (Piperaceae)

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MeJA and SA induced a differential metabolic production in elicited cell suspensions.

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Production of metabolites was dependent on the type and the concentration of elicitor.

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Elicitation with SA produced the greatest changes in the metabolic profile.

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5-hidroximetilfurfural, (Z)-9-octadecenamide and phenol were induced by elicitation.

Elicitation of cell suspensions culture is a strategy that could increase the production of secondary metabolites under controlled conditions. This research evaluated the effect of methyl jasmonate-MeJA and salicylic acid-SA as elicitors on the production of metabolites in cell suspensions of P. cumanense. The type of elicitor (MeJA or SA), the concentration of elicitor (10 μM and 100 μM), and time of exposition (3, 12, 24 h) on cell suspension were evaluated. Metabolic profiles of intracellular and extracellular extracts were analyzed by UHPLC-DAD and GC–MS. Differential production of metabolites was dependent on the type of elicitor, its concentration, and the time of exposition. Treatments with 100 μM SA were conducted to high production of 5-hydroxymethylfurfural (6.3 %), phenol (6.5 %), and (Z)-9-octadecenamide (8.8 %). This is the first report of elicitation on cell suspensions in the Piper genus and contributes to understanding the effect of MeJA and SA on metabolite production in plant cell culture.

Fast and cost-effective preparation of plant cells for scanning electron microscopy (SEM) analysis

The analysis of plant cell structure provides valuable information about its morphological, physiological, and biochemical characteristics. Nowadays, scanning electron microscope (SEM) is widely used to provide high-resolution images at the surface of biological samples. However, biological specimens require preparation, including dehydration and coating with conductive materials for imaging by SEM. There are several techniques for providing images with maximum maintenance of cell structure and minimum cellular damage, but each requires the use of expensive and hazardous materials, which can be damaging to the cell in many cases. Therefore, the provision of new and effective preparation methods based on maintaining cell structure for imaging can be very practical. In the present study, a fast and cost-effective protocol was first performed for chemical fixation and preparation of the plant cells for imaging by SEM. Taxus baccata and Zhumeria majdae cells were chemically fixed using glutaraldehyde and then successfully dried with different percentages of ethanol including 70, 80, 90, and 100%. In addition, SEM was performed for imaging the cell surface in different micro-scales. This protocol can be used by plant cell biologists and biotechnologists who are interested in studying structural and biochemical responses of treated or stressed plant cells by SEM.

Simultaneous determination of taxoids and flavonoids in twigs and leaves of three Taxus species by UHPLC-MS/MS

Taxus species are highly concerned due to the presence of anticancer taxoids (especially paclitaxel) and health beneficial flavonoids. For the first time, an UHPLC-MS/MS method was developed for the simultaneous determination of seven taxoids and seven flavonoids in twigs and leaves of three Taxus species. The satisfactory separation of fourteen target compounds was achieved within 5 min of running time on an Agilent ZORBAX Eclipse Plus C18 column (50 mm × 2.1 mm I.D., 1.8 μm) using an acetonitrile-water gradient elution program. Mass transitions of all analytes in selected reaction monitoring acquisition mode were systematically optimized for obtaining the highest signal intensities. Regression equations of all analytes exhibited excellent linearities with coefficients higher than 0.9990, and the lowest limits of quantification of all analytes ranged from 0.01 to 1.66 ng/mL. The intra- and inter-day precisions (relative standard deviations) of all analytes were less than 4.17% for retention time and less than 7.42% for peak area, and the spiking standard recoveries of all analytes ranged from 96.85%-104.77%. By the aid of the proposed method, the distribution of fourteen target compounds in twigs and leaves of Taxus chinensis, Taxus cuspidata, and Taxus media was clearly figured out. Overall, the present work provided a rapid and valid UHPLC-MS/MS approach, which could not only be useful for quality control and applicability assessment of twigs and leaves of the three Taxus species in pharmaceutical and nutraceutical industries, but also offer a good reference for the systematic analysis of taxoids and flavonoids in other Taxus species.

A common wild rice-derived BOC1 allele reduces callus browning in indica rice transformation

Callus browning, a common trait derived from the indica rice cultivar (Oryza sativa L.), is a challenge to transformation regeneration. Here, we report the map-based cloning of BROWNING OF CALLUS1 (BOC1) using a population derived from crossing Teqing, an elite indica subspecies exhibiting callus browning, and Yuanjiang, a common wild rice accession (Oryza rufipogon Griff.) that is less susceptible to callus browning. We show that BOC1 encodes a SIMILAR TO RADICAL-INDUCED CELL DEATH ONE (SRO) protein. Callus browning can be reduced by appropriate upregulation of BOC1, which consequently improves the genetic transformation efficiency. The presence of a Tourist-like miniature inverted-repeat transposable element (Tourist MITE) specific to wild rice in the promoter of BOC1 increases the expression of BOC1 in callus. BOC1 may decrease cell senescence and death caused by oxidative stress. Our study provides a gene target for improving tissue culturability and genetic transformation.

Callus browning heavily affects indica rice transformation regeneration. Here, the authors show transposon insertion in the promoter of BOC1 gene, encoding a SIMILAR TO RADICAL-INDUCED CELL DEATH ONE protein, can upregulate its expression and decrease callus browning in cultivated rice by releasing oxidative stress.

Salicylic acid as an effective elicitor for improved taxol production in endophytic fungus Pestalotiopsis microspora

Salicylic acid (SA) is an effective elicitor to increase taxol production in Pestalotiopsis microspora. Addition of SA at the concentration of 300 μM yielded taxol 625.47 μg L-1, 45- fold higher than that of the control. Elicitation of the role of SA in the fungal taxol biosynthetic pathway revealed that SA enhanced reactive oxygen species and lipid peroxidation of unsaturated fatty acids of P. microspora mycelia. This oxidative process stimulates isoprene biosynthetic pathway by triggering expression of the geranylgeranyl pyrophosphate synthase gene leading to improved biosynthesis of taxol in P. microspora.