Enhancement of tanshinone production in Salvia miltiorrhiza hairy root cultures by metabolic engineering

A high-efficient protoplast transient system for screening gene editing elements in Salvia miltiorrhiza

KEY MESSAGE

A high-efficiency protoplast transient system was devised to screen genome editing elements in Salvia miltiorrhiza. Medicinal plants with high-value pharmaceutical ingredients have attracted research attention due to their beneficial effects on human health. Cell wall-free protoplasts of plants can be used to evaluate the efficiency of genome editing mutagenesis. The capabilities of gene editing in medicinal plants remain to be fully explored owing to their complex genetic background and shortfall of suitable transformation. Here, we took the Salvia miltiorrhiza as a representative example for developing a method to screen favorable gene editing elements with high editing efficiency in medical plants by a PEG-mediated protoplast transformation. Results indicated that using the endogenous SmU6.1 of S. miltiorrhiza to drive sgRNA and the plant codon-optimized Cas9 driven by the promoter SlEF1α can enhance the efficiency of editing. In summary, we uncover an efficacious transient method for screening editing elements and shed new light on increasing gene editing efficiency in medicinal plants.

Global proteome and lysine succinylation analyses provide insights into the secondary metabolism in Salvia miltiorrhiza

Danshen, belongs to the Lamiaceae family, and its scientific name is Salvia miltiorrhiza Bunge. It is a valuable medicinal plant to prevent and treat cardiovascular and cerebrovascular diseases. Lysine succinylation, a widespread modification found in various organisms, plays a critical role in regulating secondary metabolism in plants. The hairy roots of Salvia miltiorrhiza were subject to proteomic analysis to identify lysine succinylation sites using affinity purification and HPLC-MS/MS in this investigation. Our findings reveal 566 lysine succinylation sites in 348 protein sequences. We observed 110 succinylated proteins related to secondary metabolism, totaling 210 modification sites. Our analysis identified 53 types of enzymes among the succinylated proteins, including phenylalanine ammonia-lyase (PAL) and aldehyde dehydrogenase (ALDH). PAL, a crucial enzyme involved in the biosynthesis of rosmarinic acid and flavonoids, displayed succinylation at two sites. ALDH, which participates in the phenylpropane metabolic pathway, was succinylated at 8 eight sites. These observations suggest that lysine succinylation may play a vital role in regulating the production of secondary metabolites in Salvia miltiorrhiza. Our study may provide valuable insights for further investigation on plant succinylation, specifically as a reference point. SIGNIFICANCE: Salvia miltiorrhiza Bunge is a valuable medicinal plant that prevents and treats cardiovascular and cerebrovascular diseases. Lysine succinylation plays a critical role in regulating secondary metabolism in plants. The hairy roots of Salvia miltiorrhiza were subject to proteomic analysis to identify lysine succinylation sites using affinity purification and HPLC-MS/MS in this investigation. These observations suggest that lysine succinylation may act as a vital role in regulating the production of secondary metabolites in Salvia miltiorrhiza. Our study may provide valuable insights for further investigation on succinylation in plants, specifically as a reference point.

Chromosome-level genome assembly of Salvia miltiorrhiza with orange roots uncovers the role of Sm2OGD3 in catalyzing 15,16-dehydrogenation of tanshinones

Salvia miltiorrhiza is well known for its clinical practice in treating heart and cardiovascular diseases. Its roots, used for traditional Chinese medicine materials, are usually brick-red due to accumulation of red pigments, such as tanshinone IIA and tanshinone I. Here we report a S. miltiorrhiza line (shh) with orange roots. Compared with the red roots of normal S. miltiorrhiza plants, the contents of tanshinones with a single bond at C-15,16 were increased, whereas those with a double bond at C-15,16 were significantly decreased in shh. We assembled a high-quality chromosome-level genome of shh. Phylogenomic analysis showed that the relationship between two S. miltiorrhiza lines with red roots was closer than the relationship with shh. It indicates that shh could not be the mutant of an extant S. miltiorrhiza line with red roots. Comparative genomic and transcriptomic analyses showed that a 1.0 kb DNA fragment was deleted in shh Sm2OGD3m. Complementation assay showed that overexpression of intact Sm2OGD3 in shh hairy roots recovered furan D-ring tanshinone accumulation. Consistently, in vitro protein assay showed that Sm2OGD3 catalyzed the conversion of cyptotanshinone, 15,16-dihydrotanshinone I and 1,2,15,16-tetrahydrotanshinone I into tanshinone IIA, tanshinone I and 1,2-dihydrotanshinone I, respectively. Thus, Sm2OGD3 functions as tanshinone 15,16-dehydrogenase and is a key enzyme in tanshinone biosynthesis. The results provide novel insights into the metabolic network of medicinally important tanshinone compounds.

Highly efficient Agrobacterium rhizogenes-mediated hairy root transformation for gene editing analysis in cotton

CRIPSR/Cas9 gene editing system is an effective tool for genome modification in plants. Multiple target sites are usually designed and the effective target sites are selected for editing. Upland cotton (Gossypium hirsutum L., hereafter cotton) is allotetraploid and is commonly considered as difficult and inefficient to transform, it is important to select the effective target sites that could result in the ideal transgenic plants with the CRISPR-induced mutations. In this study, Agrobacterium rhizogenes-mediated hairy root method was optimized to detect the feasibility of the target sites designed in cotton phytoene desaturase (GhPDS) gene. A. rhizogenes showed the highest hairy root induction (30%) when the bacteria were cultured until OD₆₀₀ reached to 0.8. This procedure was successfully applied to induce hairy roots in the other three cultivars (TM-1, Lumian-21, Zhongmian-49) and the mutations were detected in GhPDS induced by CRISPR/Cas9 system. Different degrees of base deletions at two sgRNAs (sgRNA5 and sgRNA10) designed in GhPDS were detected in R15 hairy roots. Furthermore, we obtained an albino transgenic cotton seeding containing CRISPR/Cas9-induced gene editing mutations in sgRNA10. The hairy root transformation system established in this study is sufficient for selecting sgRNAs in cotton, providing a technical basis for functional genomics research of cotton.

Transcriptome sequencing and signal transduction for the enhanced tanshinone production in Salvia miltiorrhiza hairy roots induced by Trichoderma atroviride D16 polysaccharide fraction

Salvia miltiorrhiza Bunge. is commonly used to treat vascular diseases because of its activity ingredients, phenolic acids, and tanshinones. Polysaccharide fraction (PSF) extracted from Trichoderma atroviride D16 could promote tanshinone accumulation in S. miltiorrhiza hairy roots. Transcriptome sequencing was conducted to describe the global gene expression of PSF-treatment hairy roots, and data analyses showed enzymes of tanshinone biosynthetic pathways were up-regulated, and genes associated to signal molecules and transcription factors were responsive. Endogenous H2O2, abscisic acid, and nitric oxide contents were measured after PSF treatment, while tanshinone accumulations were measured with treatment of exogenous H2O2 or H2O2 inhibitor on PSF-treatment S. miltiorrhiza hairy roots. The results showed H2O2 was important in tanshinone biosynthesis caused by PSF and nitric oxide might be the downstream molecules of H2O2. Taken together, the study indicates that D16 PSF enhances the accumulation of tanshinones through enzymes of tanshinone biosynthetic pathways, signal molecules, and transcription factors.

One-Step Regeneration of Hairy Roots to Induce High Tanshinone Plants in Salvia miltiorrhiza

Salvia miltiorrhiza is a traditional Chinese medicinal plant of Labiatae, which has been widely utilized to treat a variety of cardiovascular and cerebrovascular diseases. However, due to the long growth cycle, low content of active ingredients, and serious quality deterioration of S. miltiorrhiza, the use of biotechnology to improve S. miltiorrhiza to meet the growing demand for clinical applications has become a research hotspot. In this study, a novel one-step hairy root regeneration method was developed, which could rapidly obtain hairy roots and regenerated plants with high tanshinone content. By optimizing the parameters of Agrobacterium rhizogenes transformation in S. miltiorrhiza, it was finally established that the explants were infected in Ar.qual (OD₆₀₀ = 0.6) for 10 min, co-cultured for 3 days, and then screened on the screening medium containing 7.5 mg/l hygromycin, the maximum transformation frequency can reach 73.85%. GFP and PCR detection yielded a total of 9 positive transgenic hairy root lines and 11 positive transgenic regenerated plants. SmGGPPS1 was successfully overexpressed in positive transgenic regenerated plants, according to the results of qRT-PCR. The content of tanshinone IIA and cryptotanshinone were dramatically enhanced in transgenic regenerated plants and hairy roots by Ultra Performance Liquid Chromatography analysis. Based on the Agrobacterium-mediated transformation of S. miltiorrhiza, this study developed a new method for regenerating plants with transgenic hairy roots. This method provides a foundation for the breeding of S. miltiorrhiza and the sustainable development of medicinal plant resources, as well as provides a useful reference for the application of other species.

Methyl Jasmonate Activates the 2C Methyl-D-erithrytol 2,4-cyclodiphosphate Synthase Gene and Stimulates Tanshinone Accumulation in Salvia miltiorrhiza Solid Callus Cultures

The present study characterizes the 5′ regulatory region of the SmMEC gene. The isolated fragment is 1559 bp long and consists of a promoter, 5′UTR and 31 nucleotide 5′ fragments of the CDS region. In silico bioinformatic analysis found that the promoter region contains repetitions of many potential cis-active elements. Cis-active elements associated with the response to methyl jasmonate (MeJa) were identified in the SmMEC gene promoter. Co-expression studies combined with earlier transcriptomic research suggest the significant role of MeJa in SmMEC gene regulation. These findings were in line with the results of the RT-PCR test showing SmMEC gene expression induction after 72 h of MeJa treatment. Biphasic total tanshinone accumulation was observed following treatment of S. miltiorrhiza solid callus cultures with 50–500 μM methyl jasmonate, with peaks observed after 10–20 and 50–60 days. An early peak of total tanshinone concentration (0.08%) occurred after 20 days of 100 μM MeJa induction, and a second, much lower one, was observed after 50 days of 50 μM MeJa stimulation (0.04%). The dominant tanshinones were cryptotanshinone (CT) and dihydrotanshinone (DHT). To better understand the inducing effect of MeJa treatment on tanshinone biosynthesis, a search was performed for methyl jasmonate-responsive cis-active motifs in the available sequences of gene proximal promoters associated with terpenoid precursor biosynthesis. The results indicate that MeJa has the potential to induce a significant proportion of the presented genes, which is in line with available transcriptomic and RT-PCR data.

Abietane Diterpenoids from the Hairy Roots of Salvia corrugata

Salvia corrugata Vahl. is an interesting source of abietane and abeo-abietane compounds that showed antibacterial, antitumor, and cytotoxic activities. The aim of the study was to obtain transformed roots of S. corrugata and to evaluate the production of terpenoids in comparison with in vivo root production. Hairy roots were initiated from leaf explants by infection with ATCC 15834 Agrobacterium rhizogenes onto hormone-free Murashige and Skoog (MS) solid medium. Transformation was confirmed by polymerase chain reaction analysis of rolC and virC1 genes. The biomass production was obtained in hormone-free liquid MS medium using Temporary Immersion System bioreactor RITA®. The chromatographic separation of the methanolic extract of the untransformed roots afforded horminone, ferruginol, 7-O-acetylhorminone and 7-O-methylhorminone. Agastol and ferruginol were isolated and quantified from the hairy roots. The amount of these metabolites indicated that the hairy roots of S. corrugata can be considered a source of these compounds.

Xanthones Production in Gentiana dinarica Beck Hairy Root Cultures Grown in Simple Bioreactors

The hairy root clones of Gentiana dinarica cl-B, cl-D, cl-3, and cl-14 were cultivated in parallel in diverse simple bioreactors, including temporary immersion systems RITA^® (TIS RITA^®), bubble column bioreactors (BCB), and Erlenmeyer flasks (EF), and evaluated for biomass production and xanthone content. The obtained results showed that TIS RITA^® and BCB containing ½ MS medium with 4% sucrose provided equally good growth conditions in which the majority of the clones displayed the higher percentage of dry matter (DM%), and xanthones norswertianin-1-O-primeveroside (nor-1-O-prim) and norswertianin production than those cultivated in EF. Thin and well branched hairy root clone cl-B grown in BCB for 7 weeks was superior regarding all growth parameters tested, including growth index (19.97), dry weight (2.88 g), and DM% (25.70%) compared to all other clones. Cl-B cultured in TIS RITA^® contained the highest amount of nor-1-O-prim (56.82 mg per vessel). In BCB with constant aeration, cl-B accumulated the highest norswertianin content reaching 18.08 mg/vessel. The optimized conditions for cultivation of selected G. dinarica hairy root clones in highly aerated TIS RITA^® and BCB systems contribute to the development of bioreactor technology designed for the large scale commercial production of xanthones nor-1-O-prim and norswertianin.

Selected Aspects Related to Medicinal and Aromatic Plants as Alternative Sources of Bioactive Compounds

Natural compounds obtained from different medicinal and aromatic plants have gained respect as alternative treatments to synthetic drugs, as well as raw materials for different applications (cosmetic, food and feed industries, environment protection, and many others). Based on a literature survey on dedicated databases, the aim of the present work is to be a critical discussion of aspects regarding classical extraction versus modern extraction techniques; possibilities to scale up (advantages and disadvantages of different extraction methods usually applied and the influence of extraction parameters); and different medicinal and aromatic plants' different applications (medical and industrial applications, as well as the potential use in nanotechnology). As nowadays, research studies are directed toward the development of modern, innovative applications of the medicinal and aromatic plants, aspects regarding future perspectives are also discussed.

Biotransformation of xenobiotics by hairy roots

The exponential industrial growth we see today rides on the back of large scale production of chemicals, explosives and pharmaceutical products. However, the effluents getting released from their manufacturing units are greatly compromising the sustainability of our environment. With greater awareness of the imperative for environmental clean-up, a promising approach that is attracting increasing research interests is biodegradation of xenobiotics. In this approach, biotransformation has proven to be one of the most effective tools. While many different model frameworks have been used to study different aspects of biotransformation, hairy roots (HRs) have been found to be exceptionally valuable. HR cultures are preferred over other in-vitro model systems due to their biochemical stability and hormone-autotrophy. In addition, the multi-enzyme biosynthetic potential of HRs which is similar to the parent plant and their relatively low-cost cultural requirements further characterize their suitability for biotransformation. The recent progress observed in scale-up of HR cultures and understanding of functional genomics has opened up new dimensions providing valuable insights for industrial application. This review article summarizes the potential of HR cultures in the biotransformation of xenobiotics, their limitations in the application on a large scale and current strategies to alleviate them. Advancement in bioreactors engineering enabling large scale cultivation and modern gene technologies improving biotransformation efficiency promises to extend laboratory results to industrial applications.

SmbHLH53 is relevant to jasmonate signaling and plays dual roles in regulating the genes for enzymes in the pathway for salvianolic acid B biosynthesis in Salvia miltiorrhiza

Basic helix-loop-helix (bHLH) transcription factors play essential roles in myriad regulatory processes, including secondary metabolism. In this study with Salvia miltiorrhiza, we isolated and characterized SmbHLH53, which encodes a bHLH family member. Expression of this gene was significantly induced by wounding and multiple hormones, including methyl jasmonic acid; transcript levels were highest in the leaves and roots. Phylogenetic analysis indicated that SmbHLH53 clusters withAtbHLH17 and AtbHLH13, two negative regulators of jasmonate (JA) responses, and is localized in the nucleus and cell membrane. Yeast two-hybrid and bimolecular fluorescent complementation assays indicated that SmbHLH53 forms a homodimer as well as a heterodimer with SmbHLH37. It also interacts with both SmJAZs1/3/8 and SmMYC2, the core members of the JA signal pathway. Unexpectedly, we noted that overexpression of SmbHLH53 did not significantly influence the concentrations of rosmarinic acid and salvianolic acid B in transgenic plants. Results from yeast one-hybrid assays showed that SmbHLH53 binds to the promoters of SmTAT1, SmPAL1, and Sm4CL9, the key genes for enzymes in the pathway for phenolic acid synthesis. Assays of transient transcriptional activity demonstrated that SmbHLH53 represses the promoter of SmTAT1 while activating the promoter of Sm4CL9. Thus, the present work revealed that SmbHLH53 may play dual roles in regulating the genes for enzymes in the pathway for Sal B biosynthesis.

An Extract of Transgenic Senna obtusifolia L. Hairy Roots with Overexpression of PgSS1 Gene in Combination with Chemotherapeutic Agent Induces Apoptosis in the Leukemia Cell Line

Many biologically-active plant-derived compounds have therapeutic or chemopreventive effects. The use of plant in vitro cultures in conjunction with modern genetic engineering techniques allows greater amounts of valuable secondary metabolites to be obtained without interfering with the natural environment. This work presents the first findings concerning the acquisition of transgenic hairy roots of Senna obtusifolia overexpressing the gene encoding squalene synthase 1 from Panax ginseng (PgSS1) (SOPSS hairy loot lines) involved in terpenoid biosynthesis. Our results confirm that one of PgSS1-overexpressing hairy root line extracts (SOPSS2) possess a high cytotoxic effect against a human acute lymphoblastic leukemia (NALM6) cell line. Further analysis of the cell cycle, the expression of apoptosis-related genes (TP53, PUMA, NOXA, BAX) and the observed decrease in mitochondrial membrane potential also confirmed that the SOPSS2 hairy root extract displays the highest effects; similar results were also obtained for this extract combined with doxorubicin. The high cytotoxic activity, observed both alone or in combination with doxorubicin, may be due to the higher content of betulinic acid as determined by HPLC analysis. Our results suggest synergistic effects of tested extract (betulinic acid in greater amount) with doxorubicin which may be used in the future to develop new effective strategies of cancer chemosensitization.

Transgenesis as a Tool for the Efficient Production of Selected Secondary Metabolites from in Vitro Plant Cultures

The plant kingdom abounds in countless species with potential medical uses. Many of them contain valuable secondary metabolites belonging to different classes and demonstrating anticancer, anti-inflammatory, antioxidant, antimicrobial or antidiabetic properties. Many of these metabolites, e.g., paclitaxel, vinblastine, betulinic acid, chlorogenic acid or ferrulic acid, have potential applications in medicine. Additionally, these compounds have many therapeutic and health-promoting properties. The growing demand for these plant secondary metabolites forces the use of new green biotechnology tools to create new, more productive in vitro transgenic plant cultures. These procedures have yielded many promising results, and transgenic cultures have been found to be safe, efficient and cost-effective sources of valuable secondary metabolites for medicine and industry. This review focuses on the use of various in vitro plant culture systems for the production of secondary metabolites.

Boosting the Synthesis of Pharmaceutically Active Abietane Diterpenes in S. sclarea Hairy Roots by Engineering the GGPPS and CPPS Genes

Abietane diterpenoids (ADs), synthesized in the roots of different Salvia species, such as aethiopinone, 1-oxoaethiopinone, salvipisone, and ferruginol, have a variety of known biological activities. We have shown that aethiopinone has promising cytotoxic activity against several human tumor cell lines, including the breast adenocarcinoma MCF7, HeLa, epithelial carcinoma, prostate adenocarcinoma PC3, and human melanoma A375. The low content of these compounds in natural sources, and the limited possibility to synthesize them chemically at low cost, prompted us to optimize the production of abietane diterpenoids by targeting genes of the methylerythritol phosphate (MEP) pathway, from which they are derived. Here, we report our current and ongoing efforts to boost the metabolic flux towards this interesting class of compounds in Salvia sclarea hairy roots (HRs). Silencing the gene encoding the ent-copalyl-diphosphate synthase gene (entCPPS), acting at the lateral geranylgeranyl pyrophosphate (GGPP) competitive gibberellin route, enhanced the content of aethiopinone and other ADs in S. sclarea HRs, indicating indirectly that the GGPP pool is a metabolic constraint to the accumulation of ADs. This was confirmed by overexpressing the GGPPS gene (geranyl-geranyl diphosphate synthase) which triggered also a significant 8-fold increase of abietane diterpene content above the basal constitutive level, with a major boosting effect on aethiopinone accumulation in S. sclarea HRs. A significant accumulation of aethiopinone and other AD compounds was also achieved by overexpressing the CPPS gene (copalyl diphosphate synthase) pointing to this biosynthetic step as another potential metabolic target for optimizing the biosynthesis of this class of compounds. However, by co-expressing of GGPPS and CPPS genes, albeit significant, the increase of abietane diterpenoids was less effective than that obtained by overexpressing the two genes individually. Taken together, the results presented here add novel and instrumental knowledge to a rational design of a hairy root-based platform to yield reliable amounts of aethiopinone and other ADs for a deeper understanding of their molecular pharmacological targets and potential future commercialization.

UHPLC-HRMSn Analysis Reveals the Dynamic Metabonomic Responses of Salvia miltiorrhiza Hairy Roots to Polysaccharide Fraction from Trichoderma atroviride

We have previously reported that Trichoderma atroviride, an endophytic fungus isolated from S. miltiorrhiza, promotes S. miltiorrhiza hairy root growth and significantly stimulates the biosynthesis of tanshinones specifically the polysaccharide fraction (PSF). However, this study only focused exclusively on six metabolites whilst ignoring changes to the whole metabolite composition of the S. miltiorrhiza hairy roots. In the present study, the dynamic metabonomic responses of S. miltiorrhiza hairy roots were investigated using ultra-high-performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMSⁿ). UHPLC-HRMS typical total ions chromatograms (TICs) of PSF-treated hairy root samples were different from the control. Moreover, the results of principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA) and hierarchical clustering analysis (HCA) indicated that PSF-treated samples were significantly different from the control. Through the analysis of PLS-DA, a total of 114 and 99 differential metabolites were found from the positive and negative models respectively and a total of 33 differential metabolites were identified. Thus, S. miltiorrhiza hairy roots had been induced to regulate the metabolic profiling in response to PSF and the changes of the metabolic profiling contributed to promoting the biosynthesis of tanshinones notably whilst the biosynthesis of phenolic acids were slightly inhibited.

Small-Scale Bioreactor for Sterile Hydroponics and Hairy Roots: Metabolic Diversity and Salicylic Acid Exudation by Hairy Roots of Hyoscyamus niger

The volume and complexity of commercial bioreactors for sterile hydroponics and hairy roots are too large for comparative analysis of many cultures. Here a small-scale bioreactor fabricated from standard glass materials and suitable for both airlift and bubble aeration mode is described. The performance of the bioreactor was tested by growing oilseed rape (Brassica napus L.) and rose plants (Rosa canina L.) in sterile hydroponics and by cultivating hairy roots of henbane (Hyoscyamus niger L.) and sesame (Hyoscyamus niger L.). Plants grown in hydroponics for up to six weeks did not show chloroses or necroses. Hairy roots grew faster or comparably fast in bioreactors as compared to shaking flasks. Root exudates of roses and exudates of hairy roots of henbane were subjected to targeted and nontargeted analysis by HPLC coupled with optical and mass spectrometric detectors. The diversity and concentration of hairy root exudates were higher in bioreactors than in shaking flasks. The composition of hairy root exudates of three accessions of H. niger did not match the genetic relatedness among the accessions. Hairy roots of Hyoscyamus niger exuded salicylic acid in amounts varying among plant accessions and between bioreactors and shaking flask cultures.