Piriformospora indica cell wall modulates gene expression and metabolite profile in Linum album hairy roots

Modifications in gene expression and phenolic compounds content by methyl jasmonate and fungal elicitors in Ficus carica. Cv. Siah hairy root cultures

BACKGROUND

One of the most effective strategies to increase phytochemicals production in plant cultures is elicitation. In the present study, we studied the effect of abiotic and biotic elicitors on the growth, key biosynthetic genes expression, antioxidant capacity, and phenolic compounds content in Rhizobium (Agrobacterium) rhizogenes-induced hairy roots cultures of Ficus carica cv. Siah.

METHODS

The elicitors included methyl jasmonate (MeJA) as abiotic elicitor, culture filtrate and cell extract of fungus Piriformospora indica as biotic elicitors were prepared to use. The cultures of F. carica hairy roots were exposed to elicitores at different time points. After elicitation treatments, hairy roots were collected, and evaluated for growth index, total phenolic (TPC) and flavonoids (TFC) content, antioxidant activity (2,2-diphenyl-1-picrylhydrazyl, DPPH and ferric ion reducing antioxidant power, FRAP assays), expression level of key phenolic/flavonoid biosynthesis genes, and high-performance liquid chromatography (HPLC) analysis of some main phenolic compounds in comparison to control.

RESULTS

Elicitation positively or negatively affected the growth, content of phenolic/flavonoid compounds and DPPH and FRAP antioxidant activities of hairy roots cultures in depending of elicitor concentration and exposure time. The maximum expression level of chalcone synthase (CHS: 55.1), flavonoid 3'-hydroxylase (F3'H: 34.33) genes and transcription factors MYB3 (32.22), Basic helix-loop-helix (bHLH: 45.73) was induced by MeJA elicitation, whereas the maximum expression level of phenylalanine ammonia-lyase (PAL: 26.72) and UDP-glucose flavonoid 3-O-glucosyltransferase (UFGT: 27.57) genes was obtained after P. indica culture filtrate elicitation. The P. indica elicitation also caused greatest increase in the content of gallic acid (5848 µg/g), caffeic acid (508.2 µg/g), rutin (43.5 µg/g), quercetin (341 µg/g), and apigenin (1167 µg/g) phenolic compounds.

CONCLUSIONS

This study support that elicitation of F. carica cv. Siah hairy roots can be considered as an effective biotechnological method for improved phenolic/flavonoid compounds production, and of course this approach requires further research.

Methyl jasmonate redirects the dynamics of carbohydrates and amino acids toward the lignans accumulation in Linum album cells

Linum album accumulates lignans e.g., podophyllotoxin (PTOX) and 6-methoxy podophyllotoxin (6MPTOX). This study was aimed to figure out how different concentrations of MeJA (0, 50, 100, 150, and 200 μM) by affecting on free sugars and amino acids contents induce lignans accumulation in L. album cells. Results revealed that hydrogen peroxide (H₂O₂) content increased at 50μM, while it decreased at the high levels of MeJA (150 and 200 μM). Also, increasing trend of nitric oxide (NO) and lipid peroxidation levels peaked at 200 μM MeJA. An increased antioxidant enzymes activity was also observed in the treated cells. Moreover, an increase in rhamnose/xylose, glucose, and mannose was detected at 150 and 200 μM MeJA compared to the control. These compounds provide energy source and carbon skeleton for amino acids biosynthesis. Our results emphasized variations in amino acids levels in the presence of MeJA, where Phe level shifts along with synthesizing phenolics. Likewise, MeJA treatment switch on phenyl-ammonia lyase (PAL) and tyrosine-ammonia lyase (TAL) activities that regenerate phenolic compounds. Changes in phenolic acids (cinnamic, coumaric, caffeic, ferulic, and salicylic acid) and flavonoids (catechin, vitexin, myricetin, and kaempferol) were observed under MeJA treatment. Eventually, MeJA induced lignans production except for lariciresinol (LARI), so that the highest amounts of PTOX and 6MPTOX were analyzed at 50 μM, which were 4 and 5 time of control, respectively. Conclusively, it can be suggested that MeJA-induced oxidative status change redirects free sugars and amino acids toward the production of phenolic compounds especially lignans in L. album cells.

Exogenous melatonin induces phenolic compounds production in Linum album cells by altering nitric oxide and salicylic acid

Melatonin is a pleiotropic molecule that can influence various aspects of plant performance. Recent studies have exhibited that it mediates plant defensive responses, probably through managing redox homeostasis. We tried to track the regulatory effects of melatonin on the antioxidant machinery of Linum album cell culture. To this, different concentrations of melatonin were applied, and the oxidative status of cells was investigated by measuring the levels of oxidative molecules and antioxidant agents. The results showed that H₂O₂ content did not change at the low melatonin levels, while it increased at the high concentrations. It can be correlated with the low melatonin dosages capacity to remove excessive amounts of H₂O₂, while the high melatonin dosages exhibit toxicity effects. In contrast, the NO enhancement occurred at 50 μM melatonin, proposing its role in triggering melatonin-induced defensive responses. The MDA results stated that NO led to oxidative stress in melatonin-treated cells at 50 μM melatonin. Antioxidant enzyme POD was activated by melatonin treatment, while SOD enzyme behaved reversely which can explain the changes in the H₂O₂ level. In addition, the analysis of the phenolics profile showed that the contents of phenolic acids, flavonoids, and lignans enhanced following an increase in PAL enzyme activity. The increased level of phenolic hormone SA can indicate that melatonin affects the defensive responses in L. album cells through a SA-dependent pathway. In general, it seems that melatonin, by modulating NO and SA levels, can induce the activity of antioxidant enzymes and the production of phenolics, especially lignans, in L. album cells.

Hairy Root Cultures as a Source of Polyphenolic Antioxidants: Flavonoids, Stilbenoids and Hydrolyzable Tannins

Due to their chemical properties and biological activity, antioxidants of plant origin have gained interest as valuable components of the human diet, potential food preservatives and additives, ingredients of cosmetics and factors implicated in tolerance mechanisms against environmental stress. Plant polyphenols are the most prominent and extensively studied, albeit not only group of, secondary plant (specialized) metabolites manifesting antioxidative activity. Because of their potential economic importance, the productive and renewable sources of the compounds are desirable. Over thirty years of research on hairy root cultures, as both producers of secondary plant metabolites and experimental systems to investigate plant biosynthetic pathways, brought about several spectacular achievements. The present review focuses on the Rhizobium rhizogenes-transformed roots that either may be efficient sources of plant-derived antioxidants or were used to elucidate some regulatory mechanisms responsible for the enhanced accumulation of antioxidants in plant tissues.

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.

Physiological, biochemical, and molecular responses of Linum album to digested cell wall of Piriformospora indica

Plants synthesize a variety of metabolites in response to biotic elicitors. To comprehend how the digested cell wall of Piriformospora indica affects the response of ROS burst, antioxidant enzymes, amino acids profiling, and phenylpropanoid compounds such as lignans, phenolic acids, and flavonoids in Linum album hairy roots; we accomplished a time-course analysis of metabolite production and enzyme activities in response to CDCW and evaluated the metabolic profiles. The results confirms that CDCW accelerates the H₂O₂ burst and increases SOD and GPX activity in hairy roots. The HPLC analysis of metabolic profiles shows that the H₂O₂ burst shifts the amino acids, especially Phe and Tyr, fluxes toward a pool of lignans, phenolic acids, and flavonoids through alterations in the behavior of the necessary enzymes of the phenylpropanoid pathway. CDCW changes PAL, CCR, CAD, and PLR gene expression and transiently induces PTOX and 6MPROX as the main-specific products of PAL and PLR genes expression. The production of phenolic acids (e.g., cinnamic, coumaric, caffeic, and salicylic acid) and flavonoids (e.g., catechin, diosmin, kaempferol, luteolin, naringenin, daidzein, and myricetin) show different behaviors in response to CDCW. In conclusion, our observations show that CDCW elicitation can generate H₂O₂ molecules in L. album hairy roots and consequently changes physiological, biochemical, and molecular responses such as antioxidant system and the specific active compounds such as lignans. Quantification of metabolic contents in response to CDCW suggests enzyme and non-enzyme defense mechanisms play a crucial role in L. album hairy root adaptation to CDCW. A summary revealed that the correlation between H₂O₂ generation and L. album hairy root defense system under CDCW. Increase of H₂O₂ generation led plant to response against oxidative conditions. SOD, and GPX modulated H₂O₂ content, Phe, and Tyr shifted to the phenylpropanoid compounds as a precursor of PAL and TAL enzyme, the predominant phenylpropanoid compounds controlled oxidative conditions, and the other amino acids responsible for amino acid synthesis and development stages.

Piriformospora indica based elicitation for overproduction of phenolic compounds by hairy root cultures of Ficus carica

Ficus carica L. is an important source of phenolic and flavonoid compounds with valuable pharmaceutical application across various diseases. The current study was carried out to investigate the influence of Piriformospora indica elicitation on growth, production of phenolic compounds, antioxidant capacity, and expression level of flavonoid biosynthetic pathway genes in hairy root (HR) cultures of F. carica. The maximum improvement in accumulation of phenolic compounds was observed when HR culture of Ficus carica L. was exposed to 2% culture filtrate of P. indica for 72 h: gallic acid (80.5- fold), caffeic acid (26.2-fold), coumaric acid (4.5-fold), and cinnamic acid (60.1-fold), apigenin (27.6-fold) and rutin (5.7-fold). While the highest levels of chlorogenic acid (4.9-fold) and quercetin flavonoid (8.8-fold) were obtained after 48 h elicitation with culture filtrate and cell extract of P. indica at 6% (v/v), respectively. The analysis of biosynthetic genes revealed that the exposure to fungal elicitors resulted in up-regulation of phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), UDP-glucose flavonoid 3-O-glucosyltransferase (UFGT) and MYB3 transcription factor. This study shows the potential of P. indica as an efficacious elicitor for enhancing the secondary metabolites production by F. carica HRs.

Fungal Cell Wall and Methyl-β-Cyclodextrin Synergistically Enhance Paclitaxel Biosynthesis and Secretion in Corylus avellana Cell Suspension Culture

Paclitaxel is the top-selling chemotherapeutic drug used for the treatment of lung, ovarian and breast cancer as well as Kaposi's sarcoma. Cell suspension culture (CSC) of Corylus avellana has been addressed as a promising alternative for producing paclitaxel. In this study, endophytic fungus strain YEF33 was isolated from Taxus baccata and identified as Coniothyrium palmarum. The effects of the elicitors derived from this fungus including cell extract, culture filtrate and cell wall (CW) and also chitin, alone or in combination with Methyl-β-Cyclodextrin (MBCD), on paclitaxel biosynthesis in C. avellana CSC were assayed for the first time. CW of C. palmarum was the most efficient fungal elicitor for paclitaxel biosynthesis in C. avellana CSC. The results revealed that MBCD affected paclitaxel biosynthesis differently depending on fungal elicitor type and vice versa. MBCD, either alone or in combination with fungal elicitors, induced a high secretion of paclitaxel, suggesting the decrement of toxicity and retro-inhibition processes of paclitaxel for cells. The joint effects of C. palmarum CW (2.5% (v/v) on 17th day) and 50 mM MBCD synergistically enhanced paclitaxel biosynthesis (402.4 µg l-1; 5.8-fold), 78.6% of which (316.5 µg l-1) were secreted into culture medium, a level 146% higher than that in control.

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.

Pinoresinol-lariciresinol reductases, key to the lignan synthesis in plants

This paper provides an overview on activity, stereospecificity, expression and regulation of pinoresinol-lariciresinol reductases in plants. These enzymes are shared by the pathways to all 8-8' lignans derived from pinoresinol. Pinoresinol-lariciresinol reductases (PLR) are enzymes involved in the lignan biosynthesis after the initial dimerization of two monolignols. They catalyze two successive reduction steps leading to the production of lariciresinol or secoisolariciresinol from pinoresinol. Two secoisolariciresinol enantiomers can be synthetized with different fates. Depending on the plant species, these enantiomers are either final products (e.g., in the flaxseed where it is stored after glycosylation) or are the starting point for the synthesis of a wide range of lignans, among which the aryltetralin type lignans are used to semisynthesize anticancer drugs such as Etoposide^®. Thus, the regulation of the gene expression of PLRs as well as the possible specificities of these reductases for one reduction step or one enantiomer are key factors to fine-tune the lignan synthesis. Results published in the last decade have shed light on the presence of more than one PLR in each plant and revealed various modes of action. Nevertheless, there are not many results published on the PLRs and most of them were obtained in a limited range of species. Indeed, a number of them deal with wild and cultivated flax belonging to the genus Linum. Despite the occurrence of lignans in bryophytes, pteridophytes and monocots, data on PLRs in these taxa are still missing and indeed the whole diversity of PLRs is still unknown. This review summarizes the data, published mainly in the last decade, on the PLR gene expression, enzymatic activity and biological function.

RNAi-mediated silencing of pinoresinol lariciresinol reductase in Linum album hairy roots alters the phenolic accumulation in response to fungal elicitor

Lignans are diphenolic compounds produced in plants via coupling of two coniferyl alcohol molecules with the aid of a dirigent protein to form pinoresinol (PINO). The latter is reduced via lariciresinol (LARI) to secoisolariciresinol by the bifunctional pinoresinol-lariciresinol reductase (PLR). In this study, we clarified the consequences of altered lignan biosynthesis on amino acids, phenolics compounds and lignin in the hairy roots of Linum album with an ihpRNAi construct to silence PLR gene expression. Down-regulation of PLR-La1 resulted in up to an 8.3 and 3.3-time increased PINO and LARI content respectively, and reduced levels of podophyllotoxin (PTOX) and 6-methoxy podophyllotoxin (6-MPTOX). By Suppression of PLR expression, the metabolites belonging to shikimate and phenylpropanoid pathways are conducted to phenolic compounds and lignin accumulations. Although PINO and LARI were induced in response to fungal elicitor, the accumulation of PTOX and 6-MPTOX did not occur in PLR down-regulated roots. Our result also demonstrated variation in amino acids, phenolic compounds and lignin levels in presence of the fungal elicitation in PLR down regulated-roots. This data assert the accumulation of aryltetralin lignans in interactions with plant pathogens by PLR activity and the importance this enzyme for defense against pathogens in L. album.