Proteome alterations monitored by DIGE analysis in Silybum marianum cell cultures elicited with methyl jasmonate and methyl B cyclodextrin

Influence of Abiotic and Biotic Elicitors on Organogenesis, Biomass Accumulation, and Production of Key Secondary Metabolites in Asteraceae Plants

The medicinal plants of the Asteraceae family are a valuable source of bioactive secondary metabolites, including polyphenols, phenolic acids, flavonoids, acetylenes, sesquiterpene lactones, triterpenes, etc. Under stressful conditions, the plants develop these secondary substances to carry out physiological tasks in plant cells. Secondary Asteraceae metabolites that are of the greatest interest to consumers are artemisinin (an anti-malarial drug from Artemisia annua L.-sweet wormwood), steviol glycosides (an intense sweetener from Stevia rebaudiana Bert.-stevia), caffeic acid derivatives (with a broad spectrum of biological activities synthesized from Echinacea purpurea (L.) Moench-echinacea and Cichorium intybus L.-chicory), helenalin and dihydrohelenalin (anti-inflammatory drug from Arnica montana L.-mountain arnica), parthenolide ("medieval aspirin" from Tanacetum parthenium (L.) Sch.Bip.-feverfew), and silymarin (liver-protective medicine from Silybum marianum (L.) Gaertn.-milk thistle). The necessity to enhance secondary metabolite synthesis has arisen due to the widespread use of these metabolites in numerous industrial sectors. Elicitation is an effective strategy to enhance the production of secondary metabolites in in vitro cultures. Suitable technological platforms for the production of phytochemicals are cell suspension, shoots, and hairy root cultures. Numerous reports describe an enhanced accumulation of desired metabolites after the application of various abiotic and biotic elicitors. Elicitors induce transcriptional changes in biosynthetic genes, leading to the metabolic reprogramming of secondary metabolism and clarifying the mechanism of the synthesis of bioactive compounds. This review summarizes biotechnological investigations concerning the biosynthesis of medicinally essential metabolites in plants of the Asteraceae family after various elicitor treatments.

Methyl jasmonate and salicylic acid as powerful elicitors for enhancing the production of secondary metabolites in medicinal plants: an updated review

Plant secondary metabolites are bioactive scaffolds that are crucial for plant survival in the environment and to maintain a defense mechanism from predators. These compounds are generally present in plants at a minimal level and interestingly, they are found to have a wide variety of therapeutic values for humans. Several medicinal plants are used for pharmaceutical purposes due to their affordability, fewer adverse effects, and vital role in traditional remedies. Owing to this reason, these plants are exploited at a high range worldwide and therefore many medicinal plants are on the threatened list. There is a need of the hour to tackle this major problem, one effective approach called elicitation can be used to enhance the level of existing and novel plant bioactive compounds using different types of elicitors namely biotic and abiotic. This process can be generally achieved by in vitro and in vivo experiments. The current comprehensive review provides an overview of biotic and abiotic elicitation strategies used in medicinal plants, as well as their effects on secondary metabolites enhancement. Further, this review mainly deals with the enhancement of biomass and biosynthesis of different bioactive compounds by methyl jasmonate (MeJA) and salicylic acid (SA) as elicitors of wide medicinal plants in in vitro by using different cultures. The present review was suggested as a significant groundwork for peers working with medicinal plants by applying elicitation strategies along with advanced biotechnological approaches.

The Current Developments in Medicinal Plant Genomics Enabled the Diversification of Secondary Metabolites' Biosynthesis

Medicinal plants produce important substrates for their adaptation and defenses against environmental factors and, at the same time, are used for traditional medicine and industrial additives. Plants have relatively little in the way of secondary metabolites via biosynthesis. Recently, the whole-genome sequencing of medicinal plants and the identification of secondary metabolite production were revolutionized by the rapid development and cheap cost of sequencing technology. Advances in functional genomics, such as transcriptomics, proteomics, and metabolomics, pave the way for discoveries in secondary metabolites and related key genes. The multi-omics approaches can offer tremendous insight into the variety, distribution, and development of biosynthetic gene clusters (BGCs). Although many reviews have reported on the plant and medicinal plant genome, chemistry, and pharmacology, there is no review giving a comprehensive report about the medicinal plant genome and multi-omics approaches to study the biosynthesis pathway of secondary metabolites. Here, we introduce the medicinal plant genome and the application of multi-omics tools for identifying genes related to the biosynthesis pathway of secondary metabolites. Moreover, we explore comparative genomics and polyploidy for gene family analysis in medicinal plants. This study promotes medicinal plant genomics, which contributes to the biosynthesis and screening of plant substrates and plant-based drugs and prompts the research efficiency of traditional medicine.

Iridoid glycosides from Picrorhiza genus endemic to the Himalayan region: phytochemistry, biosynthesis, pharmacological potential and biotechnological intercessions to boost production

Iridoid glycosides are monoterpenoids synthesized in several plant species known to exhibit a diverse range of pharmacological activities. They are used as important bioactive ingredients in many commercially available drug formulations and as lead compounds in pharmaceutical research. The genus Picrorhiza comprises two medicinally important herbs endemic to the Himalayan region viz. Picrorhiza kurrooa Royle and Picrorhiza scrophulariiflora Hong. The medicinal properties of these two species are mainly due to iridoid glycosides present in their root, rhizome, and leaves. Unregulated harvesting from the wild, habitat specificity, narrow distribution range, small population size and lack of organized cultivation led to the enrolling of these species in the endangered category by the International Union for Conservation of Nature and Natural Resources (IUCN). Therefore, there is a need for immediate biotechnological and molecular interventions. Such intercessions will open up new vistas for large-scale propagation, development of genomic/transcriptomic resources for understanding the biosynthetic pathway, the possibility of genetic/metabolic manipulations, and possible commercialization of iridoid glycosides. The current review article elucidates the phytochemistry and pharmacological importance of iridoid glycosides from the genus Picrorhiza. In addition, the role of biotechnological approaches and opportunities offered by next-generation sequencing technologies in overcoming challenges associated with the genetic engineering of these species are also discussed.

Effect of gamma rays and colchicine on silymarin production in cell suspension cultures of Silybum marianum: A transcriptomic study of key genes involved in the biosynthetic pathway

The aim of this study was to investigate secondary metabolite production in Silybum marianum L. cell suspension cultures obtained from seeds treated with gamma rays (200 and 600 Gy) and 0.05% colchicine. The effects of these treatments on callus induction, growth, viability, and silymarin production were studied, along with the changes in the transcriptome and DNA sequence of chalcone synthase (CHS) genes. The effect of gamma radiation (200 and 600 Gy) on silymarin production in S. marianum dry seeds was also studied using HPLC-UV. All three treatments induced high callus biomass production from leaf segments. The viability of the cell suspension cultures was over 90%. The flavonolignan content measured in the extracellular culture medium of the S. marianum cell suspension was highest after treatment with 600 Gy, followed by 0.05% colchicine, and finally, 200 Gy, after a growth period of 12 days. In general, an increased expression of CHS1, CHS2, and CHS3 genes, accompanied by an increase of silymarin content, was observed in response to all the studied treatments, although the effect was greatest on CHS2 expression. Bioinformatics analysis confirmed that the three CHS2 clones exhibited the highest genetic variation, both in relation to each other and to the CHS1 and CHS3 clones. Based on the results, S. marianum plants obtained from seeds previously exposed to 600 and 200 Gy as well as colchicine constitute a renewable resource with the potential to obtain large amounts of silymarin.

Transporter and its engineering for secondary metabolites

Secondary metabolites possess a lot of biological activities, and to achieve their functions, transmembrane transportation is crucial. Elucidation of their transport mechanisms in the cell is critical for discovering ways to improve the production. Here, we have summarized the recent progresses for representative secondary metabolite transporters and also the strategies for uncovering the transporter systems in plants and microbes. We have also discussed the transporter engineering strategies being utilized for improving the heterologous natural product production, which exhibits promising future under the guide of synthetic biology.

Gene expression and flavonolignan production in fruits and cell cultures of Silybum marianum

The hepatoprotectant flavonolignan silymarin (Sm) is synthesized through 4-coumaroyl-CoA, which enters both the flavonoid and the monolignol pathway giving the two immediate precursors taxifolin (Tx) and coniferyl alcohol (CA), respectively. Sm formation occurs via oxidative radicalization of Tx and CA and is accumulated at high levels at final stages of maturation of Silybum marianum fruits. By contrast, Sm production is severely reduced in cell cultures of this species, although suspensions are able to excrete Sm compounds into the medium upon elicitation with methyl jasmonate (MeJA) or cyclodextrins (CD). Knowledge of gene expression is important to understand Sm dynamics and to develop strategies aimed at increasing production by means of cell cultures but, to date, only one gene of the pathway (chalcone synthase, SmCHS) has been cloned. Therefore, to elucidate the relationship between expression of Sm pathway genes and production of these metabolites, four cDNA fragments of genes putatively involved in flavonolignan biosynthesis, chalcone isomerase, flavanone 3-hydroxylase, flavonol 3'-hydroxylase and cinnamyl alcohol dehydrogenase, were isolated from Sm producing S. marianum fruits and their expression, together with that of the SmCHS, were studied both in fruits at different maturation stages and in elicited cell suspensions. Combined results at both transcript expression and metabolite levels at three different stages of fruit maturation revealed that the formation of the flavonoid moiety precedes flavonolignan biosynthesis, being Sm accumulation associated to expression of the monolignol pathway. There was not detectable accumulation of transcripts in cell suspensions, however, elicitation with MeJA or CD notably induced expression of the studied fragments. These results indicate that the five genes expressed during maturation of S. marianum fruits may contribute to observed increases in flavonolignan accumulation upon treatment of cell cultures with elicitors.

The role of proteomics in progressing insights into plant secondary metabolism

The development of omics has enabled the genome-wide exploration of all kinds of biological processes at the molecular level. Almost every field of plant biology has been analyzed at the genomic, transcriptomic and proteomic level. Here we focus on the particular contribution that proteomic technologies have made in progressing knowledge and characterising plant secondary metabolism (SM) pathways since early expectations were created 15 years ago. We analyzed how three major issues in the proteomic analysis of plant SM have been implemented in various research studies. These issues are: (i) the selection of a suitable plant material rich in secondary metabolites of interest, such as specialized tissues and organs, and in vitro cell cultures; (ii) the proteomic strategy to access target proteins, either a comprehensive or a differential analysis; (iii) the proteomic approach, represented by the hypothesis-free discovery proteomics and the hypothesis-driven targeted proteomics. We also examine to what extent the most-advanced technologies have been incorporated into proteomic research in plant SM and highlight some cutting edge techniques that would strongly benefit the progress made in this field.

Transport of flavonolignans to the culture medium of elicited cell suspensions of Silybum marianum

Cell suspension cultures of Silybum marianum are able to excrete silymarin compounds into the medium upon elicitation with methyl jasmonate or cyclodextrins. Knowledge of transport mechanism is important to understand Sm metabolism and to develop strategies aimed at increasing production by means of cell cultures. For these reasons, a pharmacological approach was undertaken in this work in order to elucidate the possible mechanism involved in the release of this class of secondary metabolites into the extracellular medium of suspensions. Treatment with an ionophore or NH4Cl displayed little effect in elicited cultures, thus indicating that secondary transport, which uses electrochemical gradients, is not involved in the release. Several inhibitors of ABC transporters showed differential effects. Sodium ortho-vanadate, a typical suppressor of ATPase activity, was highly toxic to cultures even at very low concentrations. The common Ca-channel blocker verapamil did not influence extracellular secondary metabolite accumulation. Glybenclamide and probenecid, both effective inhibitors of ABCC-type ABC transporters, strongly reduced silymarin secretion. A partial cDNA, SmABC1, which showed similarity to ABCC-type ABC transporters, was isolated by RT-PCR from silymarin-producing cultures. SmABC1 expression was enhanced by methyljasmonate and cyclodextrins. Brefeldin A, a fungal metabolite which affects vesicular trafficking by preventing GTP/GDP exchange, inhibited release in a dose dependent manner. These results suggest that excretion of silymarin and their precursors is a transporter-dependent active transport and that yet another mechanism involving a vesicle trafficking system seems to participate in driving this class of secondary metabolites to the extracellular compartment.