Improved cardenolide production in Calotropis gigantea hairy roots using mechanical wounding and elicitation

Deciphering the Phytochemical Potential of Hemp Hairy Roots: A Promising Source of Cannabisins and Triterpenes as Bioactive Compounds

Cannabis sativa L., specifically hemp, is a traditional herbaceous plant with industrial and medicinal uses. While much research has focused on cannabinoids and terpenes, the potential of hemp roots is less explored due to bioproduction challenges. Still, this material is rich in bioactive compounds and demonstrates promising anti-inflammatory, antimicrobial, and antioxidant properties. Biotechnological methods, such as hairy root cultures, enable the efficient production of specialized metabolites while avoiding the issues of outdoors cultures. Despite these benefits, the chemical diversity understanding of hemp hairy roots remains limited. In this study, we conducted an extensive NMR and LC/MS chemical profiling of hemp hairy roots to determine their chemical composition, revealing the presence of cannabisins for the first time. We then investigated the accumulation of cannabisins and triterpenes in both hemp hairy roots and hemp aeroponic roots. Our findings reveal that hairy roots produce 12 times more cannabisins and 6 times more triterpenes than aeroponic roots, respectively, in addition to yielding 3 times more biomass in bioreactors. Preliminary bioassays also suggest antioxidant and antifungal properties. This research underscores the potential of hemp hairy roots as a valuable source of specialized metabolites and calls for further exploration into their bioactive compounds and applications.

Elicitation enhances the production of friedelin and epifriedelanol in hairy root cultures of Cannabis sativa L

Cannabis sativa L. (hemp) has a global distribution and social impact, and it is widely used as a medicinal plant, food ingredient, and textile fiber. Its roots have received less attention than other parts, especially the inflorescence, leaves, and shoots. Triterpenoids, including friedelin and epifriedelanol, have been found in hemp roots, and their anti-inflammatory effects have been reported. In this study, the potential enhancement of triterpenoid accumulation in the roots of C. sativa by elicitation was examined. Hairy roots were successfully established, and they contained 2.02-fold higher triterpenoid levels than natural roots. Furthermore, hairy roots treated with 75 μM salicylic acid had 1.95-fold higher friedelin levels (0.963 mg/g DW) and 1.4-fold higher epifriedelanol levels (0.685 mg/g DW) than untreated hairy roots. These results suggested that the elucidation of hairy root cultures using an optimized elicitor could represent an alternative strategy to produce the valuable triterpenoids friedelin and epifriedelanol.

Biotic Elicitors in Adventitious and Hairy Root Cultures: A Review from 2010 to 2022

One of the aims of plant in vitro culture is to produce secondary plant metabolites using plant cells and organ cultures, such as cell suspensions, adventitious, and hairy roots (among others). In cases where the biosynthesis of a compound in the plant is restricted to a specific organ, unorganized systems, such as plant cell cultures, are sometimes unsuitable for biosynthesis. Then, its production is based on the establishment of organ cultures such as roots or aerial shoots. To increase the production in these biotechnological systems, elicitors have been used for years as a useful tool since they activate secondary biosynthetic pathways that control the flow of carbon to obtain different plant compounds. One important biotechnological system for the production of plant secondary metabolites or phytochemicals is root culture. Plant roots have a very active metabolism and can biosynthesize a large number of secondary compounds in an exclusive way. Some of these compounds, such as tropane alkaloids, ajmalicine, ginsenosides, etc., can also be biosynthesized in undifferentiated systems, such as cell cultures. In some cases, cell differentiation and organ formation is necessary to produce the bioactive compounds. This review analyses the biotic elicitors most frequently used in adventitious and hairy root cultures from 2010 to 2022, focusing on the plant species, the target secondary metabolite, the elicitor and its concentration, and the yield/productivity of the target compounds obtained. With this overview, it may be easier to work with elicitors in in vitro root cultures and help understand why some are more effective than others.

The Antioxidant, Cytotoxic and Antimicrobial Potential of Phenolic Acids-Enriched Extract of Elicited Hairy Roots of Salvia bulleyana

Hairy root cultures are valuable sources of a range of phytochemicals. Among them, Salvia bulleyana root culture is a promising source of polyphenols, especially rosmarinic acid (RA), a phenolic acid depside with pleiotropic activity and a wide application in medicine and cosmetology. The aim of the study was to enhance the culture productivity by finding suitable elicitation protocol and to determine its biological potential in terms of antioxidant, anticancer and antimicrobial properties. The total content of phenols and the levels of particular constituents in root extracts were analyzed using HPLC-PDA. Among four elicitors tested (yeast extract; methyl jasmonate, MJA; trans-anethol; and cadmium chloride), MJA was found to be the most effective. The greatest boost in phenolic production (up to 124.4 mg/g dry weight) was observed after three-day treatment with MJA at 100 µM, with an almost 100% improvement compared to the controls (non-treated root culture). The hydromethanolic extract from the elicited culture exhibited strong antioxidant activity with IC50 values of 11.1 µg/mL, 6.5 µg/mL and 69.5 µg/mL for DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid)) and superoxide anion radical, respectively. Moreover, in concentrations of 0.5-5 mg/mL the extract inhibited the growth of LoVo, AGS and HeLa cell lines, but was safe for the L929 cells up to the concentration of 5 mg/mL. The extract also exhibited moderate antimicrobial activity. Thus, the results confirmed that elicitation can be a beneficial strategy for increase the phenolic acid biosynthesis in hairy roots of S. bulleyana, and that such a highly productive culture can show significant biological potential.

Liquiritin elicitation can increase the content of medicinally important glucosinolates and phenolic compounds in Chinese kale plants

BACKGROUND

Brassica oleracea var. alboglabra (Chinese kale) is an important vegetable grown in southern China. This study was aimed at searching for environmentally friendly and affordable approaches to increase the production of medicinally relevant glucosinolates and phenolic compounds in Chinese kale plants. For this purpose, the foliar application of liquiritin at 0 (control), 250, 500 and 750 ppm was tested starting from the four-leaf stage and repeated every two weeks until plants were two months old.

RESULTS

Foliar application of liquiritin in Chinese kale plants significantly increased glucosinolates and total phenolic content, in a dose-dependent manner. Compared with control plants, 2.3- and 1.9-fold increases in yields of glucosinolates and total phenolic content, respectively, were corroborated in Chinese kale plants treated with 750 ppm of liquiritin. Along with rises in the content of eight different glucosinolates, liquiritin elicitation effectively increased the concentration of glycosilated and acylated flavonoids and hydroxycinnamic acids. The expression of genes involved in glucosinolate and phenolic biosynthesis was significantly higher in liquiritin-treated plants as compared to controls.

CONCLUSIONS

Liquiritin elicitation is a feasible and environmentally friendly practice for increasing the production of medicinally important glucosinolates and phenolic compounds in Chinese kale, which may improve this plant's value as a nutraceutical food. This study also contributes to understanding the molecular mechanisms underlying liquiritin elicitation. This is the first report documenting the use of liquiritin for an elicitation purpose in plants. © 2019 Society of Chemical Industry.

Elicitation: A biotechnological tool for enhanced production of secondary metabolites in hairy root cultures

Elicitation is a possible aid to overcome various difficulties associated with the large-scale production of most commercially important bioactive secondary metabolites from wild and cultivated plants, undifferentiated or differentiated cultures. Secondary metabolite accumulation in vitro or their efflux in culture medium has been elicited in the undifferentiated or differentiated tissue cultures of several plant species by the application of a low concentration of biotic and abiotic elicitors in the last three decades. Hairy root cultures are preferred for the application of elicitation due to their genetic and biosynthetic stability, high growth rate in growth regulator-free media, and production consistence in response to elicitor treatment. Elicitors act as signal, recognized by elicitor-specific receptors on the plant cell membrane and stimulate defense responses during elicitation resulting in increased synthesis and accumulation of secondary metabolites. Optimization of various parameters, such as elicitor type, concentration, duration of exposure, and treatment schedule is essential for the effectiveness of the elicitation strategies. Combined application of different elicitors, integration of precursor feeding, or replenishment of medium or in situ product recovery from the roots/liquid medium with the elicitor treatment have showed improved accumulation of secondary metabolites due to their synergistic effect. This is a comprehensive review about the progress in the elicitation approach to hairy root cultures from 2010 to 2019 and the information provided is valuable and will be of interest for scientists working in this area of plant biotechnology.

Control of β-sitosterol biosynthesis under light and watering in desert plant Calotropis procera

Most scientific studies on Calotropis procera refer to the plant as an important source of pharmaceutical compounds and its valuable benefits in medicine. One of the most important substances in this plant is the potential immunostimulant β-sitosterol (BS) that acts in improving human health. This study focused on the effects of lighting before and after irrigation on the BS accumulation pathway namely steroid biosynthesis. Studying the enzymes in BS biosynthetic pathway indicated the upregulation at dawn and predusk of the SMT2 and SMO2 genes encoding sterol methyltransferase 2 and methylsterol monooxygenase, two key enzymes in BS accumulation in C. procera. The results almost indicated no regulation at the different time points of the CYP710A gene encoding sterol 22-desaturase, an enzyme that acts in depleting β-sitosterol towards the biosynthesis of stigmasterol. RNA-Seq data was validated via quantitative RT-PCR and results were positive. The data of ultra-performance liquid chromatography-tandem mass spectrometry analysis with regard to BS accumulation also aligned with those of RNA-Seq analysis. We focused on the effects of light before and after watering on BS accumulation in C. procera. Our results show that BS accumulation is high at dawn in both dehydrated and well-watered condition. While, the BS was dramatically decrease at midday in well-watered plants. This increase/decrease in BS content is correlated with rates of expression of SMT 2 gene. This gene is a key convertor between the different branches in the cardiac glycoside biosynthesis. Accordingly, it could be suggested that BS (or one of the descendent product) may play an important role in C. procera tolerance to drought/light intensity conditions.

Transcriptome and Metabolite analysis reveal candidate genes of the cardiac glycoside biosynthetic pathway from Calotropis procera

Calotropis procera is a medicinal plant of immense importance due to its pharmaceutical active components, especially cardiac glycosides (CG). As genomic resources for this plant are limited, the genes involved in CG biosynthetic pathway remain largely unknown till date. Our study on stage and tissue specific metabolite accumulation showed that CG's were maximally accumulated in stems of 3 month old seedlings. De novo transcriptome sequencing of same was done using high throughput Illumina HiSeq platform generating 44074 unigenes with average mean length of 1785 base pair. Around 66.6% of unigenes were annotated by using various public databases and 5324 unigenes showed significant match in the KEGG database involved in 133 different pathways of plant metabolism. Further KEGG analysis resulted in identification of 336 unigenes involved in cardenolide biosynthesis. Tissue specific expression analysis of 30 putative transcripts involved in terpenoid, steroid and cardenolide pathways showed a positive correlation between metabolite and transcript accumulation. Wound stress elevated CG levels as well the levels of the putative transcripts involved in its biosynthetic pathways. This result further validated the involvement of identified transcripts in CGs biosynthesis. The identified transcripts will lay a substantial foundation for further research on metabolic engineering and regulation of cardiac glycosides biosynthesis pathway genes.

Separation and identification of candidate protein elicitors from the cultivation medium of Leptosphaeria maculans inducing resistance in Brassica napus

The Dothideomycete Leptosphaeria maculans, a worldwide fungal pathogen of oilseed rape (Brassica napus), secretes a broad spectrum of molecules into the cultivation medium during growth in vitro. Here, candidate elicitor molecules, which induce resistance in B. napus to L. maculans, were identified in the cultivation medium. The elicitation activity was indicated by increased transcription of pathogenesis-related gene 1 (PR1) and enhanced resistance of B. napus plants to the invasion of L. maculans. The elicitation activity was significantly lowered when the cultivation medium was heated to 80°C. Active components were further characterized by specific cleavage with the proteolytic enzymes trypsin and proteinase K and with glycosidases α-amylase and β-glucanase. The elicitor activity was eliminated by proteolytic digestion while glycosidases had no effect. The filtered medium was fractionated by either ion-exchange chromatography or isoelectric focusing. Mass spectrometry analysis of the most active fractions obtained by both separation procedures revealed predominantly enzymes that can be involved in the degradation of plant cell wall polysaccharides. This is the first study searching for L. maculans-specific secreted elicitors with a potential to be used as defense-activating agents in the protection of B. napus against L. maculans in agriculture. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:918-928, 2016.

Acetic acid acts as an elicitor exerting a chitosan-like effect on xanthone biosynthesis in Hypericum perforatum L. root cultures

Acetic acid acts as a signal molecule, strongly enhancing xanthone biosynthesis in Hypericum perforatum root cultures. This activity is specific, as demonstrated by the comparison with other short-chain monocarboxylic acids. We have recently demonstrated that Hypericum perforatum root cultures constitutively produce xanthones at higher levels than the root of the plant and that they respond to chitosan (CHIT) elicitation with a noteworthy increase in xanthone production. In the present study, CHIT was administered to H. perforatum root cultures using three different elicitation protocols, and the increase in xanthone production was evaluated. The best results (550 % xanthone increase) were obtained by subjecting the roots to a single elicitation with 200 mg l(-1) CHIT and maintaining the elicitor in the culture medium for 7 days. To discriminate the effect of CHIT from that of the solvent, control experiments were performed by administering AcOH alone at the same concentration used for CHIT solubilization. Unexpectedly, AcOH caused an increase in xanthone production comparable to that observed in response to CHIT. Feeding experiments with (13)C-labeled AcOH demonstrated that this compound was not incorporated into the xanthone skeleton. Other short-chain monocarboxylic acids (i.e., propionic and butyric acid) have little or no effect on the production of xanthones. These results indicate that AcOH acts as a specific signal molecule, able to greatly enhance xanthone biosynthesis in H. perforatum root cultures.

Proteins derived from in vitro culture of the callus and roots of Calotropis procera ameliorate acute inflammation in the rat paw

The callus and roots developed from the hypocotyl and cotyledon explants of the germinating seeds of Calotropis procera were grown in culture, and the proteins isolated from them (CP and RP) were evaluated for their efficacy in inhibiting edema formation induced by sub-plantar injection of carrageenan in the hind paw of rat. Intravenous administration of both CP and RP 30 min before inducing inflammation produced a dose-dependent inhibition of edema formation at 1 and 5 mg/kg doses. The extents of inhibition with these proteins ranged between 40 and 70 % at the doses included while the anti-inflammatory drug diclofenac produced 50 to 60 % inhibition at 5 mg/kg dose. The inhibitory effect with these proteins was accompanied by a dose-dependent reduction in the tissue levels of inflammatory mediators, tumor necrosis factor alpha (TNF-α) and prostaglandin E2 (PGE2), and oxidative stress markers namely glutathione and thiobarbituric acid-reactive substances and maintenance of tissue architecture. The present study shows that the proteins isolated from the differentiated and undifferentiated tissues derived from the germinating seeds have therapeutic application in the treatment of inflammatory conditions, and these tissues could be used as an alternative source to minimize variability of plant-derived formulations.

Enhanced production of valerenic acid in hairy root culture of Valeriana officinalis by elicitation

Valerenic acid (VA) is a pharmacologically-active sesquiterpene found in valerian (Valeriana officinalis L., Valerianaceae) roots and rhizomes. The plant produces only small amounts of this metabolite naturally. So, induction of hairy roots as well as elicitation can be useful to increase its commercial production. In this study, Wild-type strain ‘A13’ of Agrobacterium rhizogenes was used to induce hairy roots in valerian. The influence of three different elicitors including Fusarium graminearum extract (FE), methyl jasmonate (MJ) and salicylic acid (SA) on VA production in the selected hairy root line ‘LeVa-C4’ was also investigated. The 23-day-old cultures were treated with different concentrations of the elicitors at exposure time of 3 and 7 days. FE (1%) and MJ (100 µM L−1) highly promoted VA production at 7 days after elicitation, to a level of 12.31- and 6-fold higher than that of non-elicited controls, respectively, and FE did not exert any negative effects on biomass yield of hairy root. SA did not significantly increase the production of VA. This is the first time study to assess the elicitation of hairy root cultures to promote VA biosynthesis in valerian and the resulting experiments demonstrated that F. graminearum extract and MJ were indeed a potent inducer of VA biosynthesis.

Effects of Streptomyces pactum Act12 on Salvia miltiorrhiza hairy root growth and tanshinone synthesis and its mechanisms

The fermentation broth and mycelium pellet of Streptomyces pactum Act12 (Act12) may promote the accumulation of soluble sugar when added to Salvia miltiorrhiza hairy roots, increasing the accumulation level by as much as 23.20 % compared with the control; it may also inhibit the accumulation of soluble protein in the hairy roots, decreasing it by as much as 17.96 % compared with the control. The ACT12 also has a certain promotional effect on the growth of hairy root at an appropriate concentration of elicitors and upregulates the expression of genes 3-hydroxy-3-methyglutary1-CoA reductase (HMGR), 1-deoxy-D-xylulose 5-phosphate synthase (DXS), 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR), and geranylgeranyl diphosphate synthase (GGPPS). Among these effects, that of the HMGR gene expression is as high as 33.66 times that of the control, indicating that the test Streptomyces pactum may efficiently adjust the secondary metabolism of S. miltiorrhiza at the level of gene transcription, thereby greatly increasing the accumulation level of tanshinone in the hairy roots; among which, the cryptotanshinone levels increased most significantly, as much as 33.63 times that of the control, and the total tanshinone levels were 12.61 times that of the control.

Biotic elicitor enhanced production of psoralen in suspension cultures of Psoralea corylifolia L

Cell cultures of Psoralea corylifolia L. were established from the leaf disk derived callus. The effect of different biotic elicitors prepared from the fungal extract (Aspergillus niger and Penicillium notatum), yeast extract and chitosan with different concentrations was studied. The increased synthesis of psoralen in 16-day old cell cultures under 16 h of light and 8 h of dark period was studied. Elicitation of psoralen in A. niger elicitor treated cells was found 9-fold higher over control cells. Treating the cells with P. notatum, yeast extract and chitosan elicitors lead to four to seven-fold higher psoralen accumulation over control cells. The extract of A. niger at 1.0% v/v increased the significant accumulation of psoralen (9850 μg/g DCW) in the cultured cells. Our study clearly shows that all the elicitors had the potential to increase the accumulation of psoralen but the A. niger elicitor at 1.0% v/v induced maximum accumulation.

Methyl jasmonate mediates upregulation of bacoside A production in shoot cultures of Bacopa monnieri

Methyl jasmonate (MJ) enhances the production of a range of secondary metabolites including triterpenoid saponins in a variety of plant species. Here, it enhanced production of bacoside A, a valuable triterpenoid saponin having nootropic therapeutic activity in in vitro shoot cultures of Bacopa monnieri, the only known source of bacoside A. The highest yield was with 50 μM MJ giving 4.4 mg bacoside A/g dry wt; an 1.8-fold increase (compared to control) after 1 week.