Co-expression of AaPMT and AaTRI effectively enhances the yields of tropane alkaloids in Anisodus acutangulus hairy roots

Exogenous regulation of macronutrients promotes the accumulation of alkaloid yield in anisodus tanguticus (Maxim.) pascher

BACKGROUND

Anisodus tanguticus (Maxim.) Pascher (A. tanguticus) is a valuable botanical for extracting tropane alkaloids, which are widely used in the pharmaceutical industry. Implementing appropriate cultivation methods can improve both the quality and yield of A. tanguticus. A two-year field experiment was conducted from 2021 to 2023 using a single-factor randomized complete block design replicated three times. The study examined the effects of different nutrient levels (nitrogen: 0, 75, 150, 225, 300, 375 kg/ha; phosphorus: 0, 600, 750, 900, 1050, 1200 kg/ha; potassium: 0, 75, 112.5, 150, 187.5, 225 kg/ha) on the growth, primary alkaloid contents, and alkaloid yield of A. tanguticus at different growth stages (S-Greening, S-Growing, S-Wilting; T-Greening, T-Growing, and T-Wilting) in both the roots and aboveground portions.

RESULTS

Our results demonstrate that nutrient levels significantly affect the growth and alkaloid accumulation in A. tanguticus. High nitrogen levels (375 kg/ha) notably increased both root and aboveground biomass, while phosphorus had a minimal effect, especially on aboveground biomass. For alkaloid content (scopolamine, anisodamine, anisodine, atropine), a moderate nitrogen level (225 kg/ha) was most effective, followed by low potassium (75 kg/ha), with phosphorus showing a limited impact. Increased phosphorus levels led to a decrease in scopolamine content. During the T-Growing period, moderate nitrogen addition (225 kg/ha) yielded the highest alkaloid levels per unit area (205.79 kg/ha). In the T-Wilting period, low potassium (75 kg/ha) and low phosphorus (750 kg/ha) resulted in alkaloid levels of 146.91 kg/ha and 142.18 kg/ha, respectively. This indicates nitrogen has the most substantial effect on alkaloid accumulation, followed by potassium and phosphorus. The Douglas production function analysis suggests focusing on root biomass and the accumulation of scopolamine and atropine in roots to maximize alkaloid yield in A. tanguticus cultivation.

CONCLUSIONS

Our findings show that the optimum harvesting period for A. tanguticus is the T-Wilting period, and that the optimal nitrogen addition is 225 kg/ha, the optimal potassium addition is 75 kg/ha, and the optimal phosphorus addition is 600 kg/ha or less.

Molecular regulation of the key specialized metabolism pathways in medicinal plants

The basis of modern pharmacology is the human ability to exploit the production of specialized metabolites from medical plants, for example, terpenoids, alkaloids, and phenolic acids. However, in most cases, the availability of these valuable compounds is limited by cellular or organelle barriers or spatio-temporal accumulation patterns within different plant tissues. Transcription factors (TFs) regulate biosynthesis of these specialized metabolites by tightly controlling the expression of biosynthetic genes. Cutting-edge technologies and/or combining multiple strategies and approaches have been applied to elucidate the role of TFs. In this review, we focus on recent progress in the transcription regulation mechanism of representative high-value products and describe the transcriptional regulatory network, and future perspectives are discussed, which will help develop high-yield plant resources.

Tropinone reductase: A comprehensive review on its role as the key enzyme in tropane alkaloids biosynthesis

TAs, including hyoscyamine and scopolamine, were used to treat neuromuscular disorders ranging from nerve agent poisoning to Parkinson's disease. Tropinone reductase I (TR-I; EC 1.1.1.206) catalyzed the conversion of tropinone into tropine in the biosynthesis of TAs, directing the metabolic flow towards hyoscyamine and scopolamine. Tropinone reductase II (TR-II; EC 1.1.1.236) was responsible for the conversion of tropinone into pseudotropine, diverting the metabolic flux towards calystegine A3. The regulation of metabolite flow through both branches of the TAs pathway seemed to be influenced by the enzymatic activity of both enzymes and their accessibility to the precursor tropinone. The significant interest in the utilization of metabolic engineering for the efficient production of TAs has highlighted the importance of TRs as crucial enzymes that govern both the direction of metabolic flow and the yield of products. This review discussed recent advances for the TRs sources, properties, protein structure and biocatalytic mechanisms, and a detailed overview of its crucial role in the metabolism and synthesis of TAs was summarized. Furthermore, we conducted a detailed investigation into the evolutionary origins of these two TRs. A prospective analysis of potential challenges and applications of TRs was presented.

Hairy root culture: a potent method for improved secondary metabolite production of Solanaceous plants

Secondary metabolites synthesized by the Solanaceous plants are of major therapeutic and pharmaceutical importance, many of which are commonly obtained from the roots of these plants. 'Hairy roots', mirroring the same phytochemical pattern of the corresponding root of the parent plant with higher growth rate and productivity, are therefore extensively studied as an effective alternative for the in vitro production of these metabolites. Hairy roots are the transformed roots, generated from the infection site of the wounded plants with Agrobacterium rhizogenes. With their fast growth, being free from pathogen and herbicide contamination, genetic stability, and autotrophic nature for plant hormones, hairy roots are considered as useful bioproduction systems for specialized metabolites. Lately, several elicitation methods have been employed to enhance the accumulation of these compounds in the hairy root cultures for both small and large-scale production. Nevertheless, in the latter case, the cultivation of hairy roots in bioreactors should still be optimized. Hairy roots can also be utilized for metabolic engineering of the regulatory genes in the metabolic pathways leading to enhanced production of metabolites. The present study summarizes the updated and modern biotechnological aspects for enhanced production of secondary metabolites in the hairy root cultures of the plants of Solanaceae and their respective importance.

Metabolic engineering in hairy roots: An outlook on production of plant secondary metabolites

Plants are one of the vital sources of secondary metabolites. These secondary metabolites have diverse roles in human welfare, including therapeutic implication. Nevertheless, secondary metabolite yields obtained through the exploitation of natural plant populations is insufficient to meet the commercial demand due to their accumulation in low volumes. Besides, in-planta synthesis of these important metabolites is directly linked with the age and growing conditions of the plant. Such limitations have paved the way for the exploration of alternative production methodologies. Hairy root cultures, induced after the interaction of plants with Rhizobium rhizogenes (Agrobacterium rhizogenes), are a practical solution for producing valuable secondary metabolite at low cost and without the influence of seasonal, geographic or climatic variations. Hairy root cultures also offer the opportunity to get combined with other yield enhancements strategies (precursor feeding, elicitation and metabolic engineering) to further stimulate and/or enhance their production potential. Applications of metabolic engineering in exploiting hairy root cultures attracted the interest of several research groups as a means of yield enhancement. Currently, several engineering approaches like overexpression and silencing of pathway genes, and transcription factor overexpression are used to boost metabolite production, along with the contextual success of genome editing. This review attempts to cover metabolic engineering in hairy roots for the production of secondary metabolites, with a primary emphasis on alkaloids, and discusses prospects for taking this research forward to meet desired production demands.

Biotechnological Approaches on Engineering Medicinal Tropane Alkaloid Production in Plants

Hyoscyamine and scopolamine, belonging to medicinal tropane alkaloids (MTAs), are potent anticholinergic drugs. Their industrial production relies on medicinal plants, but the levels of the two alkaloids are very low in planta. Engineering the MTA's production is an everlasting hot topic for pharmaceutical industry. With understanding the MTA's biosynthesis, biotechnological approaches are established to produce hyoscyamine and scopolamine in an efficient manner. Great advances have been obtained in engineering MTA's production in planta. In this review, we summarize the advances on the biosynthesis of MTAs and engineering the MTA's production in hairy root cultures, as well in plants. The problems and perspectives on engineering the MTA's production are also discussed.

Application of metabolic engineering to enhance the content of alkaloids in medicinal plants

Plants are a rich source of bioactive compounds, many of which have been exploited for cosmetic, nutritional, and medicinal purposes. Through the characterization of metabolic pathways, as well as the mechanisms responsible for the accumulation of secondary metabolites, researchers have been able to increase the production of bioactive compounds in different plant species for research and commercial applications. The intent of the current review is to describe the metabolic engineering methods that have been used to transform in vitro or field-grown medicinal plants over the last decade and to identify the most effective approaches to increase the production of alkaloids. The articles summarized were categorized into six groups: endogenous enzyme overexpression, foreign enzyme overexpression, transcription factor overexpression, gene silencing, genome editing, and co-overexpression. We conclude that, because of the complex and multi-step nature of biosynthetic pathways, the approach that has been most commonly used to increase the biosynthesis of alkaloids, and the most effective in terms of fold increase, is the co-overexpression of two or more rate-limiting enzymes followed by the manipulation of regulatory genes.

Biotechnological Exploration of Transformed Root Culture for Value-Added Products

Medicinal plants produce valuable secondary metabolites with anticancer, analgesic, anticholinergic or other activities, but low metabolite levels and limited available tissue restrict metabolite yields. Transformed root cultures, also called hairy roots, provide a feasible approach for producing valuable secondary metabolites. Various strategies have been used to enhance secondary metabolite production in hairy roots, including increasing substrate availability, regulating key biosynthetic genes, multigene engineering, combining genetic engineering and elicitation, using transcription factors (TFs), and introducing new genes. In this review, we focus on recent developments in hairy roots from medicinal plants, techniques to boost production of desired secondary metabolites, and the development of new technologies to study these metabolites. We also discuss recent trends, emerging applications, and future perspectives.

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.

Enhancing Tropane Alkaloid Production Based on the Functional Identification of Tropine-Forming Reductase in Scopolia lurida, a Tibetan Medicinal Plant

Scopolia lurida, a native herbal plant species in Tibet, is one of the most effective producers of tropane alkaloids. However, the tropane alkaloid biosynthesis in this plant species of interest has yet to be studied at the molecular, biochemical, and biotechnological level. Here, we report on the isolation and characterization of a putative short chain dehydrogenase (SDR) gene. Sequence analysis showed that SlTRI belonged to the SDR family. Phylogenetic analysis revealed that SlTRI was clustered with the tropine-forming reductases. SlTRI and the other TA-biosynthesis genes, including putrescine N-methyltransferase (SlPMT) and hyoscyamine 6β-hydroxylase (SlH6H), were preferably or exclusively expressed in the S. lurida roots. The tissue profile of SlTRI suggested that this gene might be involved in tropane alkaloid biosynthesis. By using GC-MS, SlTRI was shown to catalyze the tropinone reduction to yield tropine, the key intermediate of tropane alkaloids. With the purified recombinant SlTRI from Escherichiacoli, an enzymatic assay was carried out; its result indicated that SlTRI was a tropine-forming reductase. Finally, the role of SlTRI in promoting the tropane alkaloid biosynthesis was confirmed through metabolic engineering in S. lurida. Specifically, hairy root cultures of S. lurida were established to investigate the effects of SlTRI overexpression on tropane alkaloid accumulation. In the SlTRI-overexpressing root cultures, the hyoscyamine contents were 1.7- to 2.9-fold higher than those in control while their corresponding scopolamine contents were likewise elevated. In summary, this functional identification of SlTRI has provided for a better understanding of tropane alkaloid biosynthesis. It also provides a candidate gene for enhancing tropane alkaloid biosynthesis in S. lurida via metabolic engineering.

Tropane and Granatane Alkaloid Biosynthesis: A Systematic Analysis

The tropane and granatane alkaloids belong to the larger pyrroline and piperidine classes of plant alkaloids, respectively. Their core structures share common moieties and their scattered distribution among angiosperms suggest that their biosynthesis may share common ancestry in some orders, while they may be independently derived in others. Tropane and granatane alkaloid diversity arises from the myriad modifications occurring to their core ring structures. Throughout much of human history, humans have cultivated tropane- and granatane-producing plants for their medicinal properties. This manuscript will discuss the diversity of their biological and ecological roles as well as what is known about the structural genes and enzymes responsible for their biosynthesis. In addition, modern approaches to producing some pharmaceutically important tropanes via metabolic engineering endeavors are discussed.

Enhanced Diterpene Tanshinone Accumulation and Bioactivity of Transgenic Salvia miltiorrhiza Hairy Roots by Pathway Engineering

Tanshinones are health-promoting diterpenoids found in Salvia miltiorrhiza and have wide applications. Here, SmGGPPS (geranylgeranyl diphosphate synthase) and SmDXSII (1-deoxy-D-xylulose-5-phosphate synthase) were introduced into hairy roots of S. miltiorrhiza. Overexpression of SmGGPPS and SmDXSII in hairy roots produces higher levels of tanshinone than control and single-gene transformed lines; tanshinone production in the double-gene transformed line GDII10 reached 12.93 mg/g dry weight, which is the highest tanshinone content that has been achieved through genetic engineering. Furthermore, transgenic hairy root lines showed higher antioxidant and antitumor activities than control lines. In addition, contents of chlorophylls, carotenoids, indoleacetic acid, and gibberellins were significantly elevated in transgenic Arabidopsis thaliana plants. These results demonstrate a promising method to improve the production of diterpenoids including tanshinone as well as other natural plastid-derived isoprenoids in plants by genetic manipulation of the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway.

Methyl jasmonate induction of tanshinone biosynthesis in Salvia miltiorrhiza hairy roots is mediated by JASMONATE ZIM-DOMAIN repressor proteins

Jasmonic acid (JA) is an important plant hormone involved in regulation of many aspects of plant growth and development including secondary metabolism and JASMONATE ZIM-DOMAIN (JAZ) proteins are key components in JA signal processes. In this study, two new JAZ genes named SmJAZ3 and SmJAZ9 were cloned from S. miltiorrhiza hairy roots and characterized. Expression profiles under methyl jasmonate (MJ) treatment revealed that SmJAZ3 and SmJAZ9 were both MJ-responsive. Subcellular localization assay showed that SmJAZ3 was located in nucleus while SmJAZ9 was preferentially in nucleus. Expression of SmJAZ3 and SmJAZ9 in S. miltiorrhiza hairy roots differently affected the production of tanshinone. Over-expression of SmJAZ3 or SmJAZ9 in hairy roots produced lower level of tanshinone compared with the control, tanshinone production was as low as 0.077 mg/g DW in line SmJAZ3-3 and 0.266 mg/g DW in line SmJAZ9-22. Whereas, down-regulation of SmJAZs enhanced tanshione production, the content of tanshinone increased to 2.48 fold in anti-SmJAZ3-3 line, and 1.35-fold in anti-SmJAZ9-23 line. Our work indicated that SmJAZ3 and SmJAZ9 are involved in regulation of tanshinone biosynthesis and act as repressive transcriptional regulators in the JA signaling pathway, which paves the way to further dissect molecular mechanism in details in the future.

Molecular cloning and transgenic characterization of the genes encoding chalcone synthase and chalcone isomerase from the Tibetan herbal plant Mirabilis himalaica

Mirabilis himalaica is an endangered medicinal plant species in the Tibetan Plateau. The two genes respectively encoding chalcone synthase (MhCHS) and chalcone isomerase (MhCHI) were isolated and characterized from M. himalaica. The sequence analysis revealed that the two genes were similar with their corresponding homologous genes in other plants. The tissue profiles showed that both MhCHS and MhCHI had higher expression levels in roots than in stems and leaves. Transgenic hairy root cultures respectively with overexpressing MhCHS and MhCHI were established. The genomic PCR detection confirmed the authority of transgenic hairy root lines, in which either MhCHS or MhCHI expression levels were much higher than that in non-transgenic hairy root line. Finally, the HPLC detection results demonstrated that the rotenoid contents in MhCHS/MhCHI-transformed hairy root lines were enhanced. This study provided two candidate genes that could be used to genetic engineering rotenoid biosynthesis in M. himalaica and an alternative method to produce rotenoid using transgenic hairy root cultures.

Unravelling the architecture and dynamics of tropane alkaloid biosynthesis pathways using metabolite correlation networks

The tropane alkaloid spectrum in Solanaceae is highly variable within and between species. Little is known about the topology and the coordination of the biosynthetic pathways leading to the variety of tropine and pseudotropine derived esters in the alkaloid spectrum, or about the metabolic dynamics induced by tropane alkaloid biosynthesis stimulating conditions. A good understanding of the metabolism, including all ramifications, is however necessary for the development of strategies to increase the abundance of pharmacologically interesting compounds such as hyoscyamine and scopolamine. The present study explores the tropane alkaloid metabolic pathways in an untargeted approach involving a correlation-based network analysis. Using GC-MS metabolite profiling, the variation and co-variation among tropane alkaloids and primary metabolites was monitored in 60 Datura innoxia Mill. individuals, of which half were exposed to tropane alkaloid biosynthesis stimulating conditions by co-culture with Agrobacterium rhizogenes. Considerable variation was evident in the relative proportions of the tropane alkaloids. Remodeling of the tropane alkaloid spectrum under co-culture with A. rhizogenes involved a specific and strong increase of hyoscyamine production and revealed that the accumulation of hyoscyamine, 3-tigloyloxy-6,7-epoxytropane, and 3-methylbutyryloxytropane was controlled independently of the majority of tropane alkaloids. Based on correlations between metabolites, we propose a biosynthetic origin of hygrine, the order of esterification of certain di-oxygenated tropanes, and that the rate of acetoxylation contributes to control of hyoscyamine production. Overall, this study shows that the biosynthesis of tropane alkaloids may be far more complex and finely controlled than previously expected.

WITHDRAWN: Metabolic engineering and biotechnological approaches for production of bioactive diterpene tanshinones in Salvia miltiorrhiza

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Metabolic engineering of Arabidopsis for remediation of different polycyclic aromatic hydrocarbons using a hybrid bacterial dioxygenase complex

The widespread presence of polycyclic aromatic hydrocarbons (PAHs) and their potential harm to various organisms has generated interest in efficiently eliminating these compounds from the environment. Phytoremediation is an efficient technology for cleaning up pollutants. However, unlike microorganisms, plants lack the catabolic pathway for complete degradation of these dangerous groups of compounds. One way to enhance the potential of plants for remediation of these compounds is by transferring genes involved in xenobiotic degradation from microbes to plants. In this paper, four genes, namely nidA and nidB (encoding the large and small subunits of naphthalene dioxygenase of Mycobacterium vanbaalenii PYR-1) as well as NahAa and NahAb (encoding flavoprotein reductase and ferredoxin of the electron-transport chain of the Pseudomonas putida G7 naphthalene dioxygenase system), were transferred and ectopically expressed in Arabidopsis thaliana. Transgenic Arabidopsis plants overexpressing the heterozygous naphthalene dioxygenase system exhibited enhanced tolerance toward 2-4 rings PAHs. Transgenic plants assimilated PAHs from the culture media faster and accumulated less in vivo than wild-type plants. Furthermore, examination of metabolic intermediates by gas chromatography-mass spectrometry revealed that the naphthalene metabolic pathway in transgenic plants mainly involves the dioxygenase pathway. Taken together, our findings suggest that grafting the naphthalene dioxygenase complex into plants is a possible strategy to breed PAH-tolerant plants to efficiently degrade PAHs in the environment.

Increased accumulation of the cardio-cerebrovascular disease treatment drug tanshinone in Salvia miltiorrhiza hairy roots by the enzymes 3-hydroxy-3-methylglutaryl CoA reductase and 1-deoxy-D-xylulose 5-phosphate reductoisomerase

Tanshinone is widely used for treatment of cardio-cerebrovascular diseases with increasing demand. Herein, key enzyme genes SmHMGR (3-hydroxy-3-methylglutaryl CoA reductase) and SmDXR (1-deoxy-D-xylulose 5-phosphate reductoisomerase) involved in the tanshinone biosynthetic pathway were introduced into Salvia miltiorrhiza (Sm) hairy roots to enhance tanshinone production. Over-expression of SmHMGR or SmDXR in hairy root lines can significantly enhance the yield of tanshinone. Transgenic hairy root lines co-expressing HMGR and DXR (HD lines) produced evidently higher levels of total tanshinone (TT) compared with the control and single gene transformed lines. The highest tanshinone production was observed in HD42 with the concentration of 3.25 mg g(-1) DW. Furthermore, the transgenic hairy roots showed higher antioxidant activity than control. In addition, transgenic hairy root harboring HMGR and DXR (HD42) exhibited higher tanshinone content after elicitation by yeast extract and/or Ag(+) than before. Tanshinone can be significantly enhanced to 5.858, 6.716, and 4.426 mg g(-1) DW by YE, Ag(+), and YE-Ag(+) treatment compared with non-induced HD42, respectively. The content of cryptotanshinone and dihydrotanshinone was effectively elevated upon elicitor treatments, whereas there was no obvious promotion effect for the other two compounds tanshinone I and tanshinone IIA. Our results provide a useful strategy to improve tanshinone content as well as other natural active products by combination of genetic engineering with elicitors.

Enhancing the production of tropane alkaloids in transgenic Anisodus acutangulus hairy root cultures by over-expressing tropinone reductase I and hyoscyamine-6β-hydroxylase

Tropane alkaloids (TA) including hyoscyamine, anisodamine, scopolamine and anisodine, are used medicinally as anticholinergic agents with increasing market demand, so it is very important to improve TA production by metabolic engineering strategy. Here, we report the simultaneous introduction of genes encoding the branch-controlling enzyme tropinone reductase I (TRI, EU424321) and the downstream rate-limiting enzyme hyoscyamine-6β-hydroxylase (H6H, EF187826) involved in TA biosynthesis into Anisodus acutangulus hairy roots by Agrobacterium-mediated gene transfer technology. Transgenic hairy root lines expressing both TRI and H6H (TH lines) produced significantly higher (P < 0.05) levels of TA compared with the control and single gene transformed lines (T or H lines). The best double gene transformed line (TH53) produced 4.293 mg g(-1) TA, which was about 4.49-fold higher than that of the control lines (0.96 mg g(-1)). As far as it is known, this is the first report on simultaneous introduction of TRI and H6H genes into TA-producing plant by biotechnological approaches. Besides, the content of anisodine was also greatly improved in A. acutangulus by over-expression of AaTRI and AaH6H genes. The average content of anisodine in TH lines was 0.984 mg g(-1) dw, about 18.57-fold of BC lines (0.053 mg g(-1) dw). This is the first time that this phenomenon has been found in TA-producing plants.