RNAi-mediated replacement of morphine with the nonnarcotic alkaloid reticuline in opium poppy

Novel endophytic fungal species Pithoascus kurdistanensis producing morphine compounds

Papaver genus, commonly known as popies, is a valuable source of alkaloids used in medicine, including papaverine, morphine, codeine, and thebaine. We isolated six endophytic fungal isolates producing morphinan alkaloids from four Papaver species growing in Kurdistan Province, Iran. To do this, a 1:1 mixture of methanol and chloroform was used to extract fungal cultures. The contents of morphinan alkaloids in the extracts were subsequently determined using phase high-performance liquid chromatography. Among the morphinan alkaloid-producing fungal isolates, IRAN 4653C had the highest yield giving 23.06 (mg/g) morphine and 2.03 (mg/g) codeine when grown in potato dextrose liquid medium. The identity of this isolate was examined and recognized as a new fungal species named as Pithoascus kurdistanesis sp. nov. based on multi-gene phylogenetic analyses of ITS, TEF-1α, and TUB2 sequences data and morphological features. The morphinan-producing endophytic fungus and the isolated Pithoascus species from Papaver are being reported for the first time. Accordingly, this fungus shows promise as a new source of valuable compounds which is illustrated and introduced here as a new Microascaceae member belonging to Pithoascus from Kurdistan Province, Iran. Moreover, the morphinan productivity of P. kurdistanesis was further validated by gas chromatography-mass spectrometry (GC-MS).

Herbgenomics meets Papaveraceae: a promising -omics perspective on medicinal plant research

Herbal medicines were widely used in ancient and modern societies as remedies for human ailments. Notably, the Papaveraceae family includes well-known species, such as Papaver somniferum and Chelidonium majus, which possess medicinal properties due to their latex content. Latex-bearing plants are a rich source of diverse bioactive compounds, with applications ranging from narcotics to analgesics and relaxants. With the advent of high-throughput technologies and advancements in sequencing tools, an opportunity exists to bridge the knowledge gap between the genetic information of herbs and the regulatory networks underlying their medicinal activities. This emerging discipline, known as herbgenomics, combines genomic information with other -omics studies to unravel the genetic foundations, including essential gene functions and secondary metabolite biosynthesis pathways. Furthermore, exploring the genomes of various medicinal plants enables the utilization of modern genetic manipulation techniques, such as Clustered Regularly-Interspaced Short Palindromic Repeats (CRISPR/Cas9) or RNA interference. This technological revolution has facilitated systematic studies of model herbs, targeted breeding of medicinal plants, the establishment of gene banks and the adoption of synthetic biology approaches. In this article, we provide a comprehensive overview of the recent advances in genomic, transcriptomic, proteomic and metabolomic research on species within the Papaveraceae family. Additionally, it briefly explores the potential applications and key opportunities offered by the -omics perspective in the pharmaceutical industry and the agrobiotechnology field.

Fine-tuning plant valuable secondary metabolite biosynthesis via small RNA manipulation: strategies and potential

Plants produce secondary metabolites that serve various functions, including defense against biotic and abiotic stimuli. Many of these secondary metabolites possess valuable applications in diverse fields, including medicine, cosmetic, agriculture, and food and beverage industries, exhibiting their importance in both plant biology and various human needs. Small RNAs (sRNA), such as microRNA (miRNA) and small interfering RNA (siRNA), have been shown to play significant roles in regulating the metabolic pathways post-transcriptionally by targeting specific key genes and transcription factors, thus offering a promising tool for enhancing plant secondary metabolite biosynthesis. In this review, we summarize current approaches for manipulating sRNAs to regulate secondary metabolite biosynthesis in plants. We provide an overview of the latest research strategies for sRNA manipulation across diverse plant species, including the identification of potential sRNAs involved in secondary metabolite biosynthesis in non-model plants. We also highlight the potential future research directions, focusing on the manipulation of sRNAs to produce high-value compounds with applications in pharmaceuticals, nutraceuticals, agriculture, cosmetics, and other industries. By exploring these advanced techniques, we aim to unlock new potentials for biotechnological applications, contributing to the production of high-value plant-derived products.

An update on biotechnological intervention mediated by plant tissue culture to boost secondary metabolite production in medicinal and aromatic plants

Since prehistoric times, medicinal and aromatic plants (MAPs) have been employed for various therapeutic purposes due to their varied array of pharmaceutically relevant bioactive compounds, i.e. secondary metabolites. However, when secondary metabolites are isolated directly from MAPs, there is occasionally very poor yield and limited synthesis of secondary metabolites from particular tissues and certain developmental stages. Moreover, many MAPs species are in danger of extinction, especially those used in pharmaceuticals, as their natural populations are under pressure from overharvesting due to the excess demand for plant-based herbal remedies. The extensive use of these metabolites in a number of industrial and pharmaceutical industries has prompted a call for more research into increasing the output via optimization of large-scale production using plant tissue culture techniques. The potential of plant cells as sources of secondary metabolites can be exploited through a combination of product recovery technology research, targeted metabolite production, and in vitro culture establishment. The plant tissue culture approach provides low-cost, sustainable, continuous, and viable secondary metabolite production that is not affected by geographic or climatic factors. This study covers recent advancements in the induction of medicinally relevant metabolites, as well as the conservation and propagation of plants by advanced tissue culture technologies.

Strategies, Achievements, and Potential Challenges of Plant and Microbial Chassis in the Biosynthesis of Plant Secondary Metabolites

Diverse secondary metabolites in plants, with their rich biological activities, have long been important sources for human medicine, food additives, pesticides, etc. However, the large-scale cultivation of host plants consumes land resources and is susceptible to pest and disease problems. Additionally, the multi-step and demanding nature of chemical synthesis adds to production costs, limiting their widespread application. In vitro cultivation and the metabolic engineering of plants have significantly enhanced the synthesis of secondary metabolites with successful industrial production cases. As synthetic biology advances, more research is focusing on heterologous synthesis using microorganisms. This review provides a comprehensive comparison between these two chassis, evaluating their performance in the synthesis of various types of secondary metabolites from the perspectives of yield and strategies. It also discusses the challenges they face and offers insights into future efforts and directions.

Advances in RNA Interference for Plant Functional Genomics: Unveiling Traits, Mechanisms, and Future Directions

RNA interference (RNAi) is a conserved molecular mechanism that plays a critical role in post-transcriptional gene silencing across diverse organisms. This review delves into the role of RNAi in plant functional genomics and its applications in crop improvement, highlighting its mechanistic insights and practical implications. The review begins with the foundational discovery of RNAi's mechanism, tracing its origins from petunias to its widespread presence in various organisms. Various classes of regulatory non-coding small RNAs, including siRNAs, miRNAs, and phasiRNAs, have been uncovered, expanding the scope of RNAi-mediated gene regulation beyond conventional understanding. These RNA classes participate in intricate post-transcriptional and epigenetic processes that influence gene expression. In the context of crop enhancement, RNAi has emerged as a powerful tool for understanding gene functions. It has proven effective in deciphering gene roles related to stress resistance, metabolic pathways, and more. Additionally, RNAi-based approaches hold promise for integrated pest management and sustainable agriculture, contributing to global efforts in food security. This review discusses RNAi's diverse applications, such as modifying plant architecture, extending shelf life, and enhancing nutritional content in crops. The challenges and future prospects of RNAi technology, including delivery methods and biosafety concerns, are also explored. The global landscape of RNAi research is highlighted, with significant contributions from regions such as China, Europe, and North America. In conclusion, RNAi remains a versatile and pivotal tool in modern plant research, offering novel avenues for understanding gene functions and improving crop traits. Its integration with other biotechnological approaches such as gene editing holds the potential to shape the future of agriculture and sustainable food production.

Strategies on biosynthesis and production of bioactive compounds in medicinal plants

Medicinal plants are a valuable source of essential medicines and herbal products for healthcare and disease therapy. Compared with chemical synthesis and extraction, the biosynthesis of natural products is a very promising alternative for the successful conservation of medicinal plants, and its rapid development will greatly facilitate the conservation and sustainable utilization of medicinal plants. Here, we summarize the advances in strategies and methods concerning the biosynthesis and production of natural products of medicinal plants. The strategies and methods mainly include genetic engineering, plant cell culture engineering, metabolic engineering, and synthetic biology based on multiple "OMICS" technologies, with paradigms for the biosynthesis of terpenoids and alkaloids. We also highlight the biosynthetic approaches and discuss progress in the production of some valuable natural products, exemplifying compounds such as vindoline (alkaloid), artemisinin and paclitaxel (terpenoids), to illustrate the power of biotechnology in medicinal plants.

Structural Characterization and Molecular Dynamics Study of the REPI Fusion Protein from Papaver somniferum L

REPI is a pivotal point enzyme in plant benzylisoquinoline alkaloid metabolism as it promotes the evolution of the biosynthetic branch of morphinan alkaloids. Experimental studies of its activity led to the identification of two modules (DRS and DRR) that catalyze two sequential steps of the epimerization of (S)- to (R)-reticuline. Recently, special attention has been paid to its genetic characterization and evolutionary history, but no structural analyses of the REPI protein have been conducted to date. We present here a computational structural characterization of REPI with heme and NADP cofactors in the apo state and in three complexes with substrate (S)-reticuline in DRS and intermediate 1,2-dehydroreticuline in DRS and in DRR. Since no experimental structure exists for REPI, we used its AlphaFold model as a scaffold to build up these four systems, which were submitted to all-atom molecular dynamics (MD) simulations. A comparison of MD results for the four systems revealed key dynamic changes associated with cofactor and ligand binding and provided a dynamic picture of the evolution of their structures and interactions. We also explored the possible dynamic occurrence of tunnels and electrostatic highways potentially involved in alternative mechanisms for channeling the intermediate from DRS to DRR.

Transcriptome and Metabolome Analysis of Isoquinoline Alkaloid Biosynthesis of Coptis chinensis in Different Years

Coptis chinensis is a perennial herb of the Ranunculaceae family. The isoquinoline alkaloid is the main active component of C. chinensis, mainly exists in its rhizomes and has high clinical application potential. The in vitro synthesis of isoquinoline alkaloids is difficult because their structures are complex; hence, plants are still the main source of them. In this study, two-year and four-year rhizomes of C. chinensis were selected to investigate the effect of growth years on the accumulation of isoquinoline alkaloids. Two-year and four-year C. chinensis were selected for metabolomics detection and transcriptomic analysis. A total of 413 alkaloids were detected by metabolomics analysis, of which 92 were isoquinoline alkaloids. (S)-reticuline was a significantly different accumulated metabolite of the isoquinoline alkaloids biosynthetic pathway in C. chinensis between the two groups. The results of transcriptome analysis showed that a total of 464 differential genes were identified, 36 of which were associated with the isoquinoline alkaloid biosynthesis pathway of C. chinensis. Among them, 18 genes were correlated with the content of important isoquinoline alkaloids. Overall, this study provided a comprehensive metabolomic and transcriptomic analysis of the rapid growth stage of C. chinensis rhizome from the perspective of growth years. It brought new insights into the biosynthetic pathway of isoquinoline alkaloids and provided information for utilizing biotechnology to improve their contents in C. chinensis.

A Brief Review of Plant Cell Transfection, Gene Transcript Expression, and Genotypic Integration for Enhancing Compound Production

Plants possess a plethora of important secondary metabolites, which are unique sources of natural pigments, pharmaceutical compounds, food additives, natural pesticides, and other industrial components. The commercial significance of such metabolites/compounds has directed the research toward their production and exploration of methods for enhancement of production. Biotechnological tools are critical in selecting, integrating, multiplying, improving, and analyzing medicinal plants for secondary metabolite production. Out of many techniques that are being explored to enhance secondary metabolite production, "plant cell transfection" is the latest tool to achieve maximum output from the plant source. It is based upon the introduction of foreign DNA into the plant cell relying on physical treatment such as electroporation, cell squeezing, sonoporation, optical transfection nanoparticles, magnetofection, and chemical treatment or biological treatment that depends upon carrier. One of the promising tools that have been exploited is CRISPR-Cas9. Overall, the abovementioned tools focus on the stable transfection of desired gene transcripts. Since the integration and continuous expression of transfected gene of particular trait represents stable transfection of host cell genome, resulting from transfer of required trait to daughter cells ultimately leading to enhanced production of secondary metabolites of interest. This chapter will review a set of biotechnological tools that are candidates for achieving the enhanced bioactive compound production indicated here to be used for drug discovery.

RNA Interference and CRISPR/Cas Gene Editing for Crop Improvement: Paradigm Shift towards Sustainable Agriculture

With the rapid population growth, there is an urgent need for innovative crop improvement approaches to meet the increasing demand for food. Classical crop improvement approaches involve, however, a backbreaking process that cannot equipoise with increasing crop demand. RNA-based approaches i.e., RNAi-mediated gene regulation and the site-specific nuclease-based CRISPR/Cas9 system for gene editing has made advances in the efficient targeted modification in many crops for the higher yield and resistance to diseases and different stresses. In functional genomics, RNA interference (RNAi) is a propitious gene regulatory approach that plays a significant role in crop improvement by permitting the downregulation of gene expression by small molecules of interfering RNA without affecting the expression of other genes. Gene editing technologies viz. the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein (CRISPR/Cas) have appeared prominently as a powerful tool for precise targeted modification of nearly all crops' genome sequences to generate variation and accelerate breeding efforts. In this regard, the review highlights the diverse roles and applications of RNAi and CRISPR/Cas9 system as powerful technologies to improve agronomically important plants to enhance crop yields and increase tolerance to environmental stress (biotic or abiotic). Ultimately, these technologies can prove to be important in view of global food security and sustainable agriculture.

Silencing of Oleuropein β-Glucosidase Abolishes the Biosynthetic Capacity of Secoiridoids in Olives

Specialized metabolism is an evolutionary answer that fortifies plants against a wide spectrum of (a) biotic challenges. A plethora of diversified compounds can be found in the plant kingdom and often constitute the basis of human pharmacopeia. Olive trees (Olea europaea) produce an unusual type of secoiridoids known as oleosides with promising pharmaceutical activities. Here, we transiently silenced oleuropein β-glucosidase (OeGLU), an enzyme engaged in the biosynthetic pathway of secoiridoids in the olive trees. Reduction of OeGLU transcripts resulted in the absence of both upstream and downstream secoiridoids in planta, revealing a regulatory loop mechanism that bypasses the flux of precursor compounds toward the branch of secoiridoid biosynthesis. Our findings highlight that OeGLU could serve as a molecular target to regulate the bioactive secoiridoids in olive oils.

Harnessing the natural pool of polyketide and non-ribosomal peptide family: A route map towards novel drug development

Emergence of communicable and non-communicable diseases possess health challenge to millions of people worldwide and is a major threat to the economic and social development in the coming century. The occurrence of recent pandemic, SARS-CoV-2 caused by lethal severe acute respiratory syndrome coronavirus 2 is one such example. Rapid research and development of drugs for the treatment and management of these diseases has been an incredibly challenging task for the pharmaceutical industry. Although, substantial focus has been made in the discovery of therapeutic compounds from natural sources having significant medicinal potential, their synthesis has shown a slow progress. Hence, the discovery of new targets by the application of the latest biotechnological and synthetic biology approaches is very much the need of the hour. Polyketides (PKs) and non-ribosomal peptides (NRPs) found in bacteria, fungi and plants are a large diverse family of natural products synthesized by two classes of enzymes: polyketide synthases (PKS) and non-ribosomal peptide synthetases (NRPS). These enzymes possess immense biomedical potential due to their simple architecture, catalytic capacity, as well as diversity. With the advent of latest in-silico and in-vitro strategies, these enzymes and their related metabolic pathways, if targeted, can contribute highly towards the biosynthesis of an array of potentially natural drug leads that have antagonist effects on biopolymers associated with various human diseases. In the face of the rising threat from the multidrug-resistant pathogens, this will further open new avenues for the discovery of novel and improved drugs by combining the natural and the synthetic approaches. This review discusses the relevance of polyketides and non-ribosomal peptides and the improvement strategies for the development of their derivatives and scaffolds, and how they will be beneficial to the future bioprospecting and drug discovery.

Mechanism of Mesoporous Silica Nanoparticle Interaction with Hairy Root Cultures during Nanoharvesting of Biomolecules

Cellular uptake and expulsion mechanisms of engineered mesoporous silica nanoparticles (MSNPs) are important in their design for novel biomolecule isolation and delivery applications such as nanoharvesting, defined as using nanocarriers to transport and isolate valuable therapeutics (secondary metabolites) out of living plant organ cultures (e.g., hairy roots). Here, temperature-dependent MSNP uptake and recovery processes in hairy roots are examined as a function of surface chemistry. MSNP uptake into hairy roots and time-dependent expulsion are quantified using Ti content (present for biomolecule binding) and fluorescence spectroscopy of fluorescently tagged MSNPs, respectively. The results suggest that functionalization and surface charge (regulated by amine group attachment) play the biggest role in the effectiveness of uptake and recovery. Comparison of MSNP interactions with hairy roots at 4 and 23 °C shows that weakly charged MSNPs functionalized only with Ti are taken up and expelled by thermally activated mechanisms, while amine-modified positively charged particles are taken up and expelled mainly by direct penetration of cell walls. Amine-functionalized MSNPs move spontaneously in and out of plant cells by dynamic exchange with a residence time of 20 ± 5 min, suggesting promise as a biomolecule nanoharvesting platform for plant organ cultures.

Cannabis sativa: Interdisciplinary Strategies and Avenues for Medical and Commercial Progression Outside of CBD and THC

Cannabis sativa (Cannabis) is one of the world’s most well-known, yet maligned plant species. However, significant recent research is starting to unveil the potential of Cannabis to produce secondary compounds that may offer a suite of medical benefits, elevating this unique plant species from its illicit narcotic status into a genuine biopharmaceutical. This review summarises the lengthy history of Cannabis and details the molecular pathways that underpin the production of key secondary metabolites that may confer medical efficacy. We also provide an up-to-date summary of the molecular targets and potential of the relatively unknown minor compounds offered by the Cannabis plant. Furthermore, we detail the recent advances in plant science, as well as synthetic biology, and the pharmacology surrounding Cannabis. Given the relative infancy of Cannabis research, we go on to highlight the parallels to previous research conducted in another medically relevant and versatile plant, Papaver somniferum (opium poppy), as an indicator of the possible future direction of Cannabis plant biology. Overall, this review highlights the future directions of cannabis research outside of the medical biology aspects of its well-characterised constituents and explores additional avenues for the potential improvement of the medical potential of the Cannabis plant.

Gene clustering and copy number variation in alkaloid metabolic pathways of opium poppy

Genes in plant secondary metabolic pathways enable biosynthesis of a range of medically and industrially important compounds, and are often clustered on chromosomes. Here, we study genomic clustering in the benzylisoquinoline alkaloid (BIA) pathway in opium poppy (Papaver somniferum), exploring relationships between gene expression, copy number variation, and metabolite production. We use Hi-C to improve the existing draft genome assembly, yielding chromosome-scale scaffolds that include 35 previously unanchored BIA genes. We find that co-expression of BIA genes increases within clusters and identify candidates with unknown function based on clustering and covariation in expression and alkaloid production. Copy number variation in critical BIA genes correlates with stark differences in alkaloid production, linking noscapine production with an 11-gene deletion, and increased thebaine/decreased morphine production with deletion of a T6ODM cluster. Our results show that the opium poppy genome is still dynamically evolving in ways that contribute to medically and industrially important phenotypes.

Codeinone reductase isoforms with differential stability, efficiency and product selectivity in opium poppy

Codeinone reductase (COR) catalyzes the reversible NADPH-dependent reduction of codeinone to codeine as the penultimate step of morphine biosynthesis in opium poppy (Papaver somniferum). It also irreversibly reduces neopinone, which forms by spontaneous isomerization in aqueous solution from codeinone, to neopine. In a parallel pathway involving 3-O-demethylated analogs, COR converts morphinone to morphine, and neomorphinone to neomorphine. Similar to neopine, the formation of neomorphine by COR is irreversible. Neopine is a minor substrate for codeine O-demethylase (CODM), yielding morphine. In the plant, neopine levels are low and neomorphine has not been detected. Silencing of CODM leads to accumulation of upstream metabolites, such as codeine and thebaine, but does not result in a shift towards higher relative concentrations of neopine, suggesting a mechanism in the plant for limiting neopine production. In yeast (Saccharomyces cerevisiae) engineered to produce opiate alkaloids, the catalytic properties of COR lead to accumulation of neopine and neomorphine as major products. An isoform (COR-B) was isolated from opium poppy chemotype Bea's Choice that showed higher catalytic activity than previously characterized CORs, and it yielded mostly neopine in vitro and in engineered yeast. Five catalytically distinct COR isoforms (COR1.1-1.4 and COR-B) were used to determine sequence-function relationships that influence product selectivity. Biochemical characterization and site-directed mutagenesis of native COR isoforms identified four residues (V25, K41, F129 and W279) that affected protein stability, reaction velocity, and product selectivity and output. Improvement of COR performance coupled with an ability to guide pathway flux is necessary to facilitate commercial production of opiate alkaloids in engineered microorganisms.

Herbal genomics as tools for dissecting new metabolic pathways of unexplored medicinal plants and drug discovery

Herbal drugs, on which 80% of the world's population rely, are relatively safe over conventional drugs. Conventional drugs are costly, have serious side effects and hence over the past few decades researchers have focused on drug discovery from herbal medicines or botanical sources. The majority of new herbal drugs have been generated from secondary metabolites (alkaloids, terpenoids and phenolic compounds) of plant metabolism. Till date, only a small fraction of the vast diversity of plant metabolism has been explored for the production of new medicines and other products. The emergence of new herbal genomics research, medicinal plant genomics consortium, together with advances in other omics information may help for the speedy discovery of previously unknown metabolic pathways and enzymes. This review highlights the importance of genomics research in the discovery of some previously unknown enzymes/pathways which may make significant contributions in plant metabolic biology and may be used for the future discovery of many new pharmaceutical agents.

•

New herbal drugs generated from secondary metabolites of plant metabolism.

•

Genome research can find gene clusters and gene duplication events responsible for specialized metabolism in plants.

•

Genome and other omic research helps to find genes to metabolite link.

•

This tool could be used for discovery of new pharmaceutical agents.

Green Routes for the Production of Enantiopure Benzylisoquinoline Alkaloids

Benzylisoquinoline alkaloids (BIAs) are among the most important plant secondary metabolites, in that they include a number of biologically active substances widely employed as pharmaceuticals. Isolation of BIAs from their natural sources is an expensive and time-consuming procedure as they accumulate in very low levels in plant. Moreover, total synthesis is challenging due to the presence of stereogenic centers. In view of these considerations, green and scalable methods for BIA synthesis using fully enzymatic approaches are getting more and more attention. The aim of this paper is to review fully enzymatic strategies for producing the benzylisoquinoline central precursor, (S)-norcoclaurine and its derivatives. Specifically, we will detail the current status of synthesis of BIAs in microbial hosts as well as using isolated and recombinant enzymes.

Application of 2D-HPLC coupled with principal component analysis to study an industrial opiate processing stream

Principal component analysis (PCA) loading plots were used to elucidate key differences between two-dimensional high performance liquid chromatography (2D-HPLC) fingerprint data from samples collected from stages along the Papaver somniferum industrial process chemistry workflow. Data reduction was completed using a 2D-HPLC peak picking approach as a precursor to chemometric analysis. Using comparisons of the final stages of product extraction as an example, PCA analysis of characteristic 2D-HPLC fingerprints accounted for 84.9% of variation between the two sample sets measured in triplicate, with 64.7% explained by PC1. Loadings plots of PC1 on each sample set identified where the significant changes were occurring and normalised bubble plots provided an indication of the relative importance of each of these changes. These findings highlight 2D-HPLC with appropriate chemometric analysis as a useful tool for the exploration of bioactive molecules within biomass.

Supercritical fluid extraction of papaverine and noscapine from poppy capsules followed by preconcentration with magnetic nano Fe3O4@Cu@diphenylthiocarbazone particles

A novel magnetite adsorbent modified with copper and diphenylthiocarbazone was synthesized and used as a sorbent for magnetic solid phase extraction (MSPE) of two opium alkaloids: papaverine and noscapine.

RNA Silencing in Plants: Mechanisms, Technologies and Applications in Horticultural Crops

Understanding the fundamental nature of a molecular process or a biological pathway is often a catalyst for the development of new technologies in biology. Indeed, studies from late 1990s to early 2000s have uncovered multiple overlapping but functionally distinct RNA silencing pathways in plants, including the posttranscriptional microRNA and small interfering RNA pathways and the transcriptional RNA-directed DNA methylation pathway. These findings have in turn been exploited for developing artificial RNA silencing technologies such as hairpin RNA, artificial microRNA, intrinsic direct repeat, 3' UTR inverted repeat, artificial trans-acting siRNA, and virus-induced gene silencing technologies. Some of these RNA silencing technologies, such as the hairpin RNA technology, have already been widely used for genetic improvement of crop plants in agriculture. For horticultural plants, RNA silencing technologies have been used to increase disease and pest resistance, alter plant architecture and flowering time, improve commercial traits of fruits and flowers, enhance nutritional values, remove toxic compounds and allergens, and develop high-value industrial products. In this article we aim to provide an overview of the RNA silencing pathways in plants, summarize the existing RNA silencing technologies, and review the current progress in applying these technologies for the improvement of agricultural crops particularly horticultural crops.

Identification of Novel Plasmodium falciparum Hexokinase Inhibitors with Antiparasitic Activity

Plasmodium falciparum, the deadliest species of malaria parasites, is dependent on glycolysis for the generation of ATP during the pathogenic red blood cell stage. Hexokinase (HK) catalyzes the first step in glycolysis, transferring the γ-phosphoryl group of ATP to glucose to yield glucose-6-phosphate. Here, we describe the validation of a high-throughput assay for screening small-molecule collections to identify inhibitors of the P. falciparum HK (PfHK). The assay, which employed an ADP-Glo reporter system in a 1,536-well-plate format, was robust with a signal-to-background ratio of 3.4 ± 1.2, a coefficient of variation of 6.8% ± 2.9%, and a Z'-factor of 0.75 ± 0.08. Using this assay, we screened 57,654 molecules from multiple small-molecule collections. Confirmed hits were resolved into four clusters on the basis of structural relatedness. Multiple singleton hits were also identified. The most potent inhibitors had 50% inhibitory concentrations as low as ∼1 μM, and several were found to have low-micromolar 50% effective concentrations against asexual intraerythrocytic-stage P. falciparum parasites. These molecules additionally demonstrated limited toxicity against a panel of mammalian cells. The identification of PfHK inhibitors with antiparasitic activity using this validated screening assay is encouraging, as it justifies additional HTS campaigns with more structurally amenable libraries for the identification of potential leads for future therapeutic development.

Metabolic engineering for the production of plant isoquinoline alkaloids

Several plant isoquinoline alkaloids (PIAs) possess powerful pharmaceutical and biotechnological properties. Thus, PIA metabolism and its fascinating molecules, including morphine, colchicine and galanthamine, have attracted the attention of both the industry and researchers involved in plant science, biochemistry, chemical bioengineering and medicine. Currently, access and availability of high-value PIAs [commercialized (e.g. galanthamine) or not (e.g. narciclasine)] is limited by low concentration in nature, lack of cultivation or geographic access, seasonal production and risk of overharvesting wild plant species. Nevertheless, most commercial PIAs are still extracted from plant sources. Efforts to improve the production of PIA have largely been impaired by the lack of knowledge on PIA metabolism. With the development and integration of next-generation sequencing technologies, high-throughput proteomics and metabolomics analyses and bioinformatics, systems biology was used to unravel metabolic pathways allowing the use of metabolic engineering and synthetic biology approaches to increase production of valuable PIAs. Metabolic engineering provides opportunity to overcome issues related to restricted availability, diversification and productivity of plant alkaloids. Engineered plant, plant cells and microbial cell cultures can act as biofactories by offering their metabolic machinery for the purpose of optimizing the conditions and increasing the productivity of a specific alkaloid. In this article, is presented an update on the production of PIA in engineered plant, plant cell cultures and heterologous micro-organisms.

Comparative analysis of transcription factor gene families from Papaver somniferum: identification of regulatory factors involved in benzylisoquinoline alkaloid biosynthesis

Opium poppy (Papaver somniferum L.), known for biosynthesis of several therapeutically important benzylisoquinoline alkaloids (BIAs), has emerged as the premier organism to study plant alkaloid metabolism. The most prominent molecules produced in opium poppy include narcotic analgesic morphine, the cough suppressant codeine, the muscle relaxant papaverine and the anti-microbial agent sanguinarine and berberine. Despite several health benefits, biosynthesis of some of these molecules is very low due to tight temporal and spatial regulation of the genes committed to their biosynthesis. Transcription factors, one of the prime regulators of secondary plant product biosynthesis, might be involved in controlled biosynthesis of BIAs in P. somniferum. In this study, identification of members of different transcription factor gene families using transcriptome datasets of 10 cultivars of P. somniferum with distinct chemoprofile has been carried out. Analysis suggests that most represented transcription factor gene family in all the poppy cultivars is WRKY. Comparative transcriptome analysis revealed differential expression pattern of the members of a set of transcription factor gene families among 10 cultivars. Through analysis, two members of WRKY and one member of C3H gene family were identified as potential candidates which might regulate thebaine and papaverine biosynthesis, respectively, in poppy.

Functional Characterization of 4'OMT and 7OMT Genes in BIA Biosynthesis

Alkaloids are diverse group of secondary metabolites generally found in plants. Opium poppy (Papaver somniferum L.), the only commercial source of morphinan alkaloids, has been used as a medicinal plant since ancient times. It produces benzylisoquinoline alkaloids (BIA) including the narcotic analgesic morphine, the muscle relaxant papaverine, and the anti-cancer agent noscapine. Though BIAs play crucial roles in many biological mechanisms their steps in biosynthesis and the responsible genes remain to be revealed. In this study, expressions of 3-hydroxy-N-methylcoclaurine 4'-methyltransferase (4'OMT) and reticuline 7-O-methyltransferase (7OMT) genes were subjected to manipulation to functionally characterize their roles in BIA biosynthesis. Measurements of alkaloid accumulation were performed in leaf, stem, and capsule tissues accordingly. Suppression of 4'OMT expression caused reduction in the total alkaloid content in stem tissue whereas total alkaloid content was significantly induced in the capsule. Silencing of the 7OMT gene also caused repression in total alkaloid content in the stem. On the other hand, over-expression of 4'OMT and 7OMT resulted in higher morphine accumulation in the stem but suppressed amount in the capsule. Moreover, differential expression in several BIA synthesis genes (CNMT, TYDC, 6OMT, SAT, COR, 4'OMT, and 7OMT) were observed upon manipulation of 4'OMT and 7OMT expression. Upon silencing and overexpression applications, tissue specific effects of these genes were identified. Manipulation of 4'OMT and 7OMT genes caused differentiated accumulation of BIAs including morphine and noscapine in capsule and stem tissues.

Total biosynthesis of opiates by stepwise fermentation using engineered Escherichia coli

Opiates such as morphine and codeine are mainly obtained by extraction from opium poppies. Fermentative opiate production in microbes has also been investigated, and complete biosynthesis of opiates from a simple carbon source has recently been accomplished in yeast. Here we demonstrate that Escherichia coli serves as an efficient, robust and flexible platform for total opiate synthesis. Thebaine, the most important raw material in opioid preparations, is produced by stepwise culture of four engineered strains at yields of 2.1 mg l(-1) from glycerol, corresponding to a 300-fold increase from recently developed yeast systems. This improvement is presumably due to strong activity of enzymes related to thebaine synthesis from (R)-reticuline in E. coli. Furthermore, by adding two genes to the thebaine production system, we demonstrate the biosynthesis of hydrocodone, a clinically important opioid. Improvements in opiate production in this E. coli system represent a major step towards the development of alternative opiate production systems.

Pterin-Dependent Mono-oxidation for the Microbial Synthesis of a Modified Monoterpene Indole Alkaloid

Monoterpene indole alkaloids (MIAs) have important therapeutic value, including as anticancer and antimalarial agents. Because of their chemical complexity, therapeutic MIAs, or advanced intermediates thereof, are often isolated from the native plants. The microbial synthesis of MIAs would allow for the rapid and scalable production of complex MIAs and MIA analogues for therapeutic use. Here, we produce the modified MIA hydroxystrictosidine from glucose and the monoterpene secologanin via a pterin-dependent mono-oxidation strategy. Specifically, we engineered the yeast Saccharomyces cerevisiae for the high-level synthesis of tetrahydrobiopterin to mono-oxidize tryptophan to 5-hydroxytryptophan, which, after decarboxylation to serotonin, is coupled to exogenously fed secologanin to produce 10-hydroxystrictosidine in an eight-enzyme pathway. We selected hydroxystrictosidine as our synthetic target because hydroxylation at the 10' position of the alkaloid core strictosidine provides a chemical handle for the future chemical semisynthesis of therapeutics. We show the generality of the pterin-dependent mono-oxidation strategy for alkaloid synthesis by hydroxylating tyrosine to L-DOPA-a key intermediate in benzylisoquinoline alkaloid (BIA) biosynthesis-and, thereafter, further converting it to dopamine. Together, these results present the first microbial synthesis of a modified alkaloid, the first production of tetrahydrobiopterin in yeast, and the first use of a pterin-dependent mono-oxidation strategy for the synthesis of L-DOPA. This work opens the door to the scalable production of MIAs as well as the production of modified MIAs to serve as late intermediates in the semisynthesis of known and novel therapeutics. Further, the microbial strains in this work can be used as plant pathway discovery tools to elucidate known MIA biosynthetic pathways or to identify pathways leading to novel MIAs.

Generation of Triple-Transgenic Forsythia Cell Cultures as a Platform for the Efficient, Stable, and Sustainable Production of Lignans

Sesamin is a furofuran lignan biosynthesized from the precursor lignan pinoresinol specifically in sesame seeds. This lignan is shown to exhibit anti-hypertensive activity, protect the liver from damages by ethanol and lipid oxidation, and reduce lung tumor growth. Despite rapidly elevating demand, plant sources of lignans are frequently limited because of the high cost of locating and collecting plants. Indeed, the acquisition of sesamin exclusively depends on the conventional extraction of particular Sesamum seeds. In this study, we have created the efficient, stable and sustainable sesamin production system using triple-transgenic Forsythia koreana cell suspension cultures, U18i-CPi-Fk. These transgenic cell cultures were generated by stably introducing an RNAi sequence against the pinoresinol-glucosylating enzyme, UGT71A18, into existing CPi-Fk cells, which had been created by introducing Sesamum indicum sesamin synthase (CYP81Q1) and an RNA interference (RNAi) sequence against pinoresinol/lariciresinol reductase (PLR) into F. koreanna cells. Compared to its transgenic prototype, U18i-CPi-Fk displayed 5-fold higher production of pinoresinol aglycone and 1.4-fold higher production of sesamin, respectively, while the wildtype cannot produce sesamin due to a lack of any intrinsic sesamin synthase. Moreover, red LED irradiation of U18i-CPi-Fk specifically resulted in 3.0-fold greater production in both pinoresinol aglycone and sesamin than production of these lignans under the dark condition, whereas pinoresinol production was decreased in the wildtype under red LED. Moreover, we developed a procedure for sodium alginate-based long-term storage of U18i-CPi-Fk in liquid nitrogen. Production of sesamin in U18i-CPi-Fk re-thawed after six-month cryopreservation was equivalent to that of non-cryopreserved U18i-CPi-Fk. These data warrant on-demand production of sesamin anytime and anywhere. Collectively, the present study provides evidence that U18i-CP-Fk is an unprecedented platform for efficient, stable, and sustainable production of sesamin, and shows that a transgenic and specific light-regulated Forsythia cell-based metabolic engineering is a promising strategy for the acquisition of rare and beneficial lignans.

Complete biosynthesis of opioids in yeast

Opioids are the primary drugs used in Western medicine for pain management and palliative care. Farming of opium poppies remains the sole source of these essential medicines, despite diverse market demands and uncertainty in crop yields due to weather, climate change, and pests. We engineered yeast to produce the selected opioid compounds thebaine and hydrocodone starting from sugar. All work was conducted in a laboratory that is permitted and secured for work with controlled substances. We combined enzyme discovery, enzyme engineering, and pathway and strain optimization to realize full opiate biosynthesis in yeast. The resulting opioid biosynthesis strains required the expression of 21 (thebaine) and 23 (hydrocodone) enzyme activities from plants, mammals, bacteria, and yeast itself. This is a proof of principle, and major hurdles remain before optimization and scale-up could be achieved. Open discussions of options for governing this technology are also needed in order to responsibly realize alternative supplies for these medically relevant compounds.

Tilting Plant Metabolism for Improved Metabolite Biosynthesis and Enhanced Human Benefit

The immense chemical diversity of plant-derived secondary metabolites coupled with their vast array of biological functions has seen this group of compounds attract considerable research interest across a range of research disciplines. Medicinal and aromatic plants, in particular, have been exploited for this biogenic pool of phytochemicals for products such as pharmaceuticals, fragrances, dyes, and insecticides, among others. With consumers showing increasing interests in these products, innovative biotechnological techniques are being developed and employed to alter plant secondary metabolism in efforts to improve on the quality and quantity of specific metabolites of interest. This review provides an overview of the biosynthesis for phytochemical compounds with medicinal and other related properties and their associated biological activities. It also provides an insight into how their biosynthesis/biosynthetic pathways have been modified/altered to enhance production.

Stereochemical inversion of (S)-reticuline by a cytochrome P450 fusion in opium poppy

The gateway to morphine biosynthesis in opium poppy (Papaver somniferum) is the stereochemical inversion of (S)-reticuline since the enzyme yielding the first committed intermediate salutaridine is specific for (R)-reticuline. A fusion between a cytochrome P450 (CYP) and an aldo-keto reductase (AKR) catalyzes the S-to-R epimerization of reticuline via 1,2-dehydroreticuline. The reticuline epimerase (REPI) fusion was detected in opium poppy and in Papaver bracteatum, which accumulates thebaine. In contrast, orthologs encoding independent CYP and AKR enzymes catalyzing the respective synthesis and reduction of 1,2-dehydroreticuline were isolated from Papaver rhoeas, which does not accumulate morphinan alkaloids. An ancestral relationship between these enzymes is supported by a conservation of introns in the gene fusions and independent orthologs. Suppression of REPI transcripts using virus-induced gene silencing in opium poppy reduced levels of (R)-reticuline and morphinan alkaloids and increased the overall abundance of (S)-reticuline and its O-methylated derivatives. Discovery of REPI completes the isolation of genes responsible for known steps of morphine biosynthesis.

Plant science. Morphinan biosynthesis in opium poppy requires a P450-oxidoreductase fusion protein

Morphinan alkaloids from the opium poppy are used for pain relief. The direction of metabolites to morphinan biosynthesis requires isomerization of (S)- to (R)-reticuline. Characterization of high-reticuline poppy mutants revealed a genetic locus, designated STORR [(S)- to (R)-reticuline] that encodes both cytochrome P450 and oxidoreductase modules, the latter belonging to the aldo-keto reductase family. Metabolite analysis of mutant alleles and heterologous expression demonstrate that the P450 module is responsible for the conversion of (S)-reticuline to 1,2-dehydroreticuline, whereas the oxidoreductase module converts 1,2-dehydroreticuline to (R)-reticuline rather than functioning as a P450 redox partner. Proteomic analysis confirmed that these two modules are contained on a single polypeptide in vivo. This modular assembly implies a selection pressure favoring substrate channeling. The fusion protein STORR may enable microbial-based morphinan production.

Changing trends in biotechnology of secondary metabolism in medicinal and aromatic plants

Medicinal and aromatic plants are known to produce secondary metabolites that find uses as flavoring agents, fragrances, insecticides, dyes and drugs. Biotechnology offers several choices through which secondary metabolism in medicinal plants can be altered in innovative ways, to overproduce phytochemicals of interest, to reduce the content of toxic compounds or even to produce novel chemicals. Detailed investigation of chromatin organization and microRNAs affecting biosynthesis of secondary metabolites as well as exploring cryptic biosynthetic clusters and synthetic biology options, may provide additional ways to harness this resource. Plant secondary metabolites are a fascinating class of phytochemicals exhibiting immense chemical diversity. Considerable enigma regarding their natural biological functions and the vast array of pharmacological activities, amongst other uses, make secondary metabolites interesting and important candidates for research. Here, we present an update on changing trends in the biotechnological approaches that are used to understand and exploit the secondary metabolism in medicinal and aromatic plants. Bioprocessing in the form of suspension culture, organ culture or transformed hairy roots has been successful in scaling up secondary metabolite production in many cases. Pathway elucidation and metabolic engineering have been useful to get enhanced yield of the metabolite of interest; or, for producing novel metabolites. Heterologous expression of putative plant secondary metabolite biosynthesis genes in a microbe is useful to validate their functions, and in some cases, also, to produce plant metabolites in microbes. Endophytes, the microbes that normally colonize plant tissues, may also produce the phytochemicals produced by the host plant. The review also provides perspectives on future research in the field.

A microbial biomanufacturing platform for natural and semisynthetic opioids

Opiates and related molecules are medically essential, but their production via field cultivation of opium poppy Papaver somniferum leads to supply inefficiencies and insecurity. As an alternative production strategy, we developed baker's yeast Saccharomyces cerevisiae as a microbial host for the transformation of opiates. Yeast strains engineered to express heterologous genes from P. somniferum and bacterium Pseudomonas putida M10 convert thebaine to codeine, morphine, hydromorphone, hydrocodone and oxycodone. We discovered a new biosynthetic branch to neopine and neomorphine, which diverted pathway flux from morphine and other target products. We optimized strain titer and specificity by titrating gene copy number, enhancing cosubstrate supply, applying a spatial engineering strategy and performing high-density fermentation, which resulted in total opioid titers up to 131 mg/l. This work is an important step toward total biosynthesis of valuable benzylisoquinoline alkaloid drug molecules and demonstrates the potential for developing a sustainable and secure yeast biomanufacturing platform for opioids.

Benzylisoquinoline alkaloid biosynthesis in opium poppy

Opium poppy (Papaver somniferum) is one of the world's oldest medicinal plants and remains the only commercial source for the narcotic analgesics morphine, codeine and semi-synthetic derivatives such as oxycodone and naltrexone. The plant also produces several other benzylisoquinoline alkaloids with potent pharmacological properties including the vasodilator papaverine, the cough suppressant and potential anticancer drug noscapine and the antimicrobial agent sanguinarine. Opium poppy has served as a model system to investigate the biosynthesis of benzylisoquinoline alkaloids in plants. The application of biochemical and functional genomics has resulted in a recent surge in the discovery of biosynthetic genes involved in the formation of major benzylisoquinoline alkaloids in opium poppy. The availability of extensive biochemical genetic tools and information pertaining to benzylisoquinoline alkaloid metabolism is facilitating the study of a wide range of phenomena including the structural biology of novel catalysts, the genomic organization of biosynthetic genes, the cellular and sub-cellular localization of biosynthetic enzymes and a variety of biotechnological applications. In this review, we highlight recent developments and summarize the frontiers of knowledge regarding the biochemistry, cellular biology and biotechnology of benzylisoquinoline alkaloid biosynthesis in opium poppy.

RNA interference: concept to reality in crop improvement

The phenomenon of RNA interference (RNAi) is involved in sequence-specific gene regulation driven by the introduction of dsRNA resulting in inhibition of translation or transcriptional repression. Since the discovery of RNAi and its regulatory potentials, it has become evident that RNAi has immense potential in opening a new vista for crop improvement. RNAi technology is precise, efficient, stable and better than antisense technology. It has been employed successfully to alter the gene expression in plants for better quality traits. The impact of RNAi to improve the crop plants has proved to be a novel approach in combating the biotic and abiotic stresses and the nutritional improvement in terms of bio-fortification and bio-elimination. It has been employed successfully to bring about modifications of several desired traits in different plants. These modifications include nutritional improvements, reduced content of food allergens and toxic compounds, enhanced defence against biotic and abiotic stresses, alteration in morphology, crafting male sterility, enhanced secondary metabolite synthesis and seedless plant varieties. However, crop plants developed by RNAi strategy may create biosafety risks. So, there is a need for risk assessment of GM crops in order to make RNAi a better tool to develop crops with biosafety measures. This article is an attempt to review the RNAi, its biochemistry, and the achievements attributed to the application of RNAi in crop improvement.

Non-coding RNAs in crop genetic modification: considerations and predictable environmental risk assessments (ERA)

Of late non-coding RNAs (ncRNAs)-mediated gene silencing is an influential tool deliberately deployed to negatively regulate the expression of targeted genes. In addition to the widely employed small interfering RNA (siRNA)-mediated gene silencing approach, other variants like artificial miRNA (amiRNA), miRNA mimics, and artificial transacting siRNAs (tasiRNAs) are being explored and successfully deployed in developing non-coding RNA-based genetically modified plants. The ncRNA-based gene manipulations are typified with mobile nature of silencing signals, interference from viral genome-derived suppressor proteins, and an obligation for meticulous computational analysis to prevaricate any inadvertent effects. In a broad sense, risk assessment inquiries for genetically modified plants based on the expression of ncRNAs are competently addressed by the environmental risk assessment (ERA) models, currently in vogue, designed for the first generation transgenic plants which are based on the expression of heterologous proteins. Nevertheless, transgenic plants functioning on the foundation of ncRNAs warrant due attention with respect to their unique attributes like off-target or non-target gene silencing effects, small RNAs (sRNAs) persistence, food and feed safety assessments, problems in detection and tracking of sRNAs in food, impact of ncRNAs in plant protection measures, effect of mutations etc. The role of recent developments in sequencing techniques like next generation sequencing (NGS) and the ERA paradigm of the different countries in vogue are also discussed in the context of ncRNA-based gene manipulations.

Transcriptome and metabolome analysis of plant sulfate starvation and resupply provides novel information on transcriptional regulation of metabolism associated with sulfur, nitrogen and phosphorus nutritional responses in Arabidopsis

Sulfur is an essential macronutrient for plant growth and development. Reaching a thorough understanding of the molecular basis for changes in plant metabolism depending on the sulfur-nutritional status at the systems level will advance our basic knowledge and help target future crop improvement. Although the transcriptional responses induced by sulfate starvation have been studied in the past, knowledge of the regulation of sulfur metabolism is still fragmentary. This work focuses on the discovery of candidates for regulatory genes such as transcription factors (TFs) using 'omics technologies. For this purpose a short term sulfate-starvation/re-supply approach was used. ATH1 microarray studies and metabolite determinations yielded 21 TFs which responded more than 2-fold at the transcriptional level to sulfate starvation. Categorization by response behaviors under sulfate-starvation/re-supply and other nutrient starvations such as nitrate and phosphate allowed determination of whether the TF genes are specific for or common between distinct mineral nutrient depletions. Extending this co-behavior analysis to the whole transcriptome data set enabled prediction of putative downstream genes. Additionally, combinations of transcriptome and metabolome data allowed identification of relationships between TFs and downstream responses, namely, expression changes in biosynthetic genes and subsequent metabolic responses. Effect chains on glucosinolate and polyamine biosynthesis are discussed in detail. The knowledge gained from this study provides a blueprint for an integrated analysis of transcriptomics and metabolomics and application for the identification of uncharacterized genes.

Natural products - modifying metabolite pathways in plants

The diversity of plant natural product (PNP) molecular structures is reflected in the variety of biochemical and genetic pathways that lead to their formation and accumulation. Plant secondary metabolites are important commodities, and include fragrances, colorants, and medicines. Increasing the extractable amount of PNP through plant breeding, or more recently by means of metabolic engineering, is a priority. The prerequisite for any attempt at metabolic engineering is a detailed knowledge of the underlying biosynthetic and regulatory pathways in plants. Over the past few decades, an enormous body of information about the biochemistry and genetics of biosynthetic pathways involved in PNPs production has been generated. In this review, we focus on the three large classes of plant secondary metabolites: terpenoids (or isoprenoids), phenylpropanoids, and alkaloids. All three provide excellent examples of the tremendous efforts undertaken to boost our understanding of biosynthetic pathways, resulting in the first successes in plant metabolic engineering. We further consider what essential information is still missing, and how future research directions could help achieve the rational design of plants as chemical factories for high-value products.

MicroRNA-mediated gene regulation: potential applications for plant genetic engineering

Food security is one of the most important issues challenging the world today. Any strategies to solve this problem must include increasing crop yields and quality. MicroRNA-based genetic modification technology (miRNA-based GM tech) can be one of the most promising solutions that contribute to agricultural productivity directly by developing superior crop cultivars with enhanced biotic and abiotic stress tolerance and increased biomass yields. Indirectly, the technology may increase usage of marginal soils and decrease pesticide use, among other benefits. This review highlights the most recent progress of transgenic studies utilizing various miRNAs and their targets for plant trait modifications, and analyzes the potential of miRNA-mediated gene regulation for use in crop improvement. Strategies for manipulating miRNAs and their targets in transgenic plants including constitutive, stress-induced, or tissue-specific expression of miRNAs or their targets, RNA interference, expressing miRNA-resistant target genes, artificial target mimic and artificial miRNAs were discussed. We also discussed potential risks of utilizing miRNA-based GM tech. In general, miRNAs and their targets not only provide an invaluable source of novel transgenes, but also inspire the development of several new GM strategies, allowing advances in breeding novel crop cultivars with agronomically useful characteristics.

Metabolic engineering and in vitro biosynthesis of phytochemicals and non-natural analogues

Over the years, natural products from plants and their non-natural derivatives have shown to be active against different types of chronic diseases. However, isolation of such natural products can be limited due to their low bioavailability, and environmental restrictions. To address these issues, in vivo and in vitro reconstruction of plant metabolic pathways and the metabolic engineering of microbes and plants have been used to generate libraries of compounds. Significant advances have been made through metabolic engineering of microbes and plant cells to generate a variety of compounds (e.g. isoprenoids, flavonoids, or stilbenes) using a diverse array of methods to optimize these processes (e.g. host selection, operational variables, precursor selection, gene modifications). These approaches have been used also to generate non-natural analogues with different bioactivities. In vitro biosynthesis allows the synthesis of intermediates as well as final products avoiding post-translational limitations. Moreover, this strategy allows the use of substrates and the production of metabolites that could be toxic for cells, or expand the biosynthesis into non-conventional media (e.g. organic solvents, supercritical fluids). A perspective is also provided on the challenges for generating novel chemical structures and the potential of combining metabolic engineering and in vitro biocatalysis to produce metabolites with more potent biological activities.