Molecular cloning and characterization of norcoclaurine synthase, an enzyme catalyzing the first committed step in benzylisoquinoline alkaloid biosynthesis

Developing benzylisoquinoline alkaloid-enriched opium poppy via CRISPR-directed genome editing: A review

Among plant-derived secondary metabolites are benzylisoquinoline alkaloids (BIAs) that play a vital role in medicine. The most conspicuous BIAs frequently found in opium poppy are morphine, codeine, thebaine, papaverine, sanguinarine, and noscapine. BIAs have provided abundant clinically useful drugs used in the treatment of various diseases and ailments With an increasing demand for these herbal remedies, genetic improvement of poppy plants appears to be essential to live up to the expectations of the pharmaceutical industry. With the advent of clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated9 (Cas9), the field of metabolic engineering has undergone a paradigm shift in its approach due to its appealing attributes, such as the transgene-free editing capability, precision, selectivity, robustness, and versatility. The potentiality of the CRISPR system for manipulating metabolic pathways in opium poppy was demonstrated, but further investigations regarding the use of CRISPR in BIA pathway engineering should be undertaken to develop opium poppy into a bioreactor synthesizing BIAs at the industrial-scale levels. In this regard, the recruitment of RNA-guided genome editing for knocking out miRNAs, flower responsible genes, genes involved in competitive pathways, and base editing are described. The approaches presented here have never been suggested or applied in opium poppy so far.

Unveiling Amaryllidaceae alkaloids: from biosynthesis to antiviral potential - a review

Covering: 2017 to 2023 (now)Amaryllidaceae alkaloids (AAs) are a unique class of specialized metabolites containing heterocyclic nitrogen bridging that play a distinct role in higher plants. Irrespective of their diverse structures, most AAs are biosynthesized via intramolecular oxidative coupling. The complex organization of biosynthetic pathways is constantly enlightened by new insights owing to the advancement of natural product chemistry, synthetic organic chemistry, biochemistry, systems and synthetic biology tools and applications. These promote novel compound identification, trace-level metabolite quantification, synthesis, and characterization of enzymes engaged in AA catalysis, enabling the recognition of biosynthetic pathways. A complete understanding of the pathway benefits biotechnological applications in the long run. This review emphasizes the structural diversity of the AA specialized metabolites involved in biogenesis although the process is not entirely defined yet. Moreover, this work underscores the pivotal role of synthetic and enantioselective studies in justifying biosynthetic conclusions. Their prospective candidacy as lead constituents for antiviral drug discovery has also been established. However, a complete understanding of the pathway requires further interdisciplinary efforts in which antiviral studies address the structure-activity relationship. This review presents current knowledge on the topic.

Promising approaches for simultaneous enhancement of medicinally significant benzylisoquinoline alkaloids in opium poppy

Benzylisoquinoline alkaloids (BIAs) produced in opium poppy have been evidenced to heal patients suffering from various diseases. They, therefore, hold an integral position in the herbal drug industry. Despite the adoption of several approaches for the large-scale production of BIAs, opium poppy remains the only platform in this purpose. The only disadvantage associated with producing BIAs in the plant is their small quantity. Thus, recruiting strategies that boost their levels is deemed necessary. All the methods which have been employed so far are just able to enhance a maximum of two BIAs. Thus, if these methods are utilized, a sizable amount of time and budget must be spent on the synthesis of all BIAs. Hence, the exploitation of strategies which increase the content of all BIAs at the same time is more commercially effective and time-saving, avoiding the laborious step of resolving the biosynthetic pathway of each compound. Exposure to biotic and abiotic elicitors, development of a synthetic auto-tetraploid, overexpression of a WRKY transcription factor, formation of an artificial metabolon, and suppression of a gene in the shikimate pathway and miRNA are strategies that turn opium poppy into a versatile bioreactor for the concurrent and massive production of BIAs. The last three strategies have never been applied for BIA biosynthetic pathways.

Cepharanthine analogs mining and genomes of Stephania accelerate anti-coronavirus drug discovery

Cepharanthine is a secondary metabolite isolated from Stephania. It has been reported that it has anti-conronaviruses activities including severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Here, we assemble three Stephania genomes (S. japonica, S. yunnanensis, and S. cepharantha), propose the cepharanthine biosynthetic pathway, and assess the antiviral potential of compounds involved in the pathway. Among the three genomes, S. japonica has a near telomere-to-telomere assembly with one remaining gap, and S. cepharantha and S. yunnanensis have chromosome-level assemblies. Following by biosynthetic gene mining and metabolomics analysis, we identify seven cepharanthine analogs that have broad-spectrum anti-coronavirus activities, including SARS-CoV-2, Guangxi pangolin-CoV (GX_P2V), swine acute diarrhoea syndrome coronavirus (SADS-CoV), and porcine epidemic diarrhea virus (PEDV). We also show that two other genera, Nelumbo and Thalictrum, can produce cepharanthine analogs, and thus have the potential for antiviral compound discovery. Results generated from this study could accelerate broad-spectrum anti-coronavirus drug discovery.

Genome-wide identification of rubber tree pathogenesis-related 10 (PR-10) proteins with biological relevance to plant defense

Pathogenesis-related 10 (PR-10) is a group of small intracellular proteins that is one of 17 subclasses of pathogenesis-related proteins in plants. The PR-10 proteins have been studied extensively and are well-recognized for their contribution to host defense against phytopathogens in several plant species. Interestingly, the accumulation of PR-10 proteins in the rubber tree, one of the most economically important crops worldwide, after being infected by pathogenic organisms has only recently been reported. In this study, the homologous proteins of the PR-10 family were systemically identified from the recently available rubber tree genomes in the NCBI database. The sequence compositions, structural characteristics, protein physical properties, and phylogenetic relationships of identified PR-10 proteins in rubber trees support their classification into subgroups, which mainly consist of Pru ar 1-like major allergens and major latex-like (MLP) proteins. The rubber tree PR10-encoding genes were majorly clustered on chromosome 15. The potential roles of rubber tree PR-10 proteins are discussed based on previous reports. The homologous proteins in the PR-10 family were identified in the recent genomes of rubber trees and were shown to be crucial in host responses to biotic challenges. The genome-wide identification conducted here will accelerate the future study of rubber tree PR-10 proteins. A better understanding of these defense-related proteins may contribute to alternative ways of developing rubber tree clones with desirable traits in the future.

Subcellular compartmentalization in the biosynthesis and engineering of plant natural products

Plant natural products (PNPs) are specialized metabolites with diverse bioactivities. They are extensively used in the pharmaceutical, cosmeceutical and food industries. PNPs are synthesized in plant cells by enzymes that are distributed in different subcellular compartments with unique microenvironments, such as ions, co-factors and substrates. Plant metabolic engineering is an emerging and promising approach for the sustainable production of PNPs, for which the knowledge of the subcellular compartmentalization of their biosynthesis is instrumental. In this review we describe the state of the art on the role of subcellular compartments in the biosynthesis of major types of PNPs, including terpenoids, phenylpropanoids, alkaloids and glucosinolates, and highlight the efforts to target biosynthetic pathways to subcellular compartments in plants. In addition, we will discuss the challenges and strategies in the field of plant synthetic biology and subcellular engineering. We expect that newly developed methods and tools, together with the knowledge gained from the microbial chassis, will greatly advance plant metabolic engineering.

Constructing an artificial short route for cell-free biosynthesis of the phenethylisoquinoline scaffold

Plant-originated natural products are important drug sources. However, total biosynthesis of these compounds is often not achievable due to their uncharacterized, lengthy biosynthetic pathways. In nature, phenethylisoquinoline alkaloids (PIAs) such as colchicine are biosynthesized via a common precursor 6,7-dihydroxy-1-(4-hydroxyphenylethyl)-1,2,3,4-tetrahydroisoquinoline (i.e., phenethylisoquinoline scaffold, PIAS). PIAS is naturally synthesized in plants by using two upstream substrates (l-phenylalanine and l-tyrosine) catalyzed by eight enzymes. To shorten this native pathway, here we designed an artificial route to synthesize PIAS with two enzymatic steps from two alternative substrates of 3-(4-hydroxyphenyl) propanol (4-HPP) and dopamine. In the two-step bioconversion, an alcohol dehydrogenase selected from yeast (i.e., ADH7) was able to oxidize its non-native alcohol substrate 4-HPP to form the corresponding aldehyde product, which was then condensed with dopamine by the (S)-norcoclaurine synthase (NCS) to synthesize PIAS. After optimization, the final enzymatic reaction system was successfully scaled up by 200 times from 50 μL to 10 mL, generating 5.4 mM of PIAS. We envision that this study will provide an easy and sustainable approach to produce PIAS and thus lay the foundation for large-scale production of PIAS-derived natural products.

Characterization of norbelladine synthase and noroxomaritidine/norcraugsodine reductase reveals a novel catalytic route for the biosynthesis of Amaryllidaceae alkaloids including the Alzheimer's drug galanthamine

Amaryllidaceae alkaloids (AAs) are a large group of plant specialized metabolites with diverse pharmacological properties. Norbelladine is the entry compound in AAs biosynthesis and is produced from the condensation of tyramine and 3,4-dihydroxybenzaldehyde (3,4-DHBA). There are two reported enzymes capable of catalyzing this reaction in-vitro, both with low yield. The first one, norbelladine synthase (NBS), was shown to condense tyramine and 3,4-DHBA, while noroxomaritidine/norcraugsodine reductase (NR), catalyzes a reduction reaction to produce norbelladine. To clarify the mechanisms involved in this controversial step, both NBS and NR homologs were identified from the transcriptome of Narcissus papyraceus and Leucojum aestivum, cloned and expressed in Escherichia coli. Enzymatic assays performed with tyramine and 3,4-DHBA with each enzyme separately or combined, suggested that NBS and NR function together for the condensation of tyramine and 3,4-DHBA into norcraugsodine and further reduction into norbelladine. Using molecular homology modeling and docking studies, we predicted models for the binding of tyramine and 3,4-DHBA to NBS, and of the intermediate norcraugsodine to NR. Moreover, we show that NBS and NR physically interact in yeast and in-planta, that both localize to the cytoplasm and nucleus and are expressed at high levels in bulbs, confirming their colocalization and co-expression thus their ability to work together in the same catalytic route. Finally, their co-expression in yeast led to the production of norbelladine. In all, our study establishes that both NBS and NR participate in the biosynthesis of norbelladine by catalyzing the first key steps associated in the biosynthesis of the Alzheimer's drug galanthamine.

Rational Engineering of (S)-Norcoclaurine Synthase for Efficient Benzylisoquinoline Alkaloids Biosynthesis

(S)-Norcoclaurine is synthesized in vivo through a metabolic pathway that ends with (S)-norcoclaurine synthase (NCS). The former constitutes the scaffold for the biosynthesis of all benzylisoquinoline alkaloids (BIAs), including many drugs such as the opiates morphine and codeine and the semi-synthetic opioids oxycodone, hydrocodone, and hydromorphone. Unfortunately, the only source of complex BIAs is the opium poppy, leaving the drug supply dependent on poppy crops. Therefore, the bioproduction of (S)-norcoclaurine in heterologous hosts, such as bacteria or yeast, is an intense area of research nowadays. The efficiency of (S)-norcoclaurine biosynthesis is strongly dependent on the catalytic efficiency of NCS. Therefore, we identified vital NCS rate-enhancing mutations through the rational transition-state macrodipole stabilization method at the Quantum Mechanics/Molecular Mechanics (QM/MM) level. The results are a step forward for obtaining NCS variants able to biosynthesize (S)-norcoclaurine on a large scale.

A novel rubber tree PR-10 protein involved in host-defense response against the white root rot fungus Rigidoporus microporus

BACKGROUND

White root rot disease in rubber trees, caused by the pathogenic fungi Rigidoporus microporus, is currently considered a major problem in rubber tree plantations worldwide. Only a few reports have mentioned the response of rubber trees occurring at the non-infection sites, which is crucial for the disease understanding and protecting the yield losses.

RESULTS

Through a comparative proteomic study using the two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) technique, the present study reveals some distal-responsive proteins in rubber tree leaves during the plant-fungal pathogen interaction. From a total of 12 selected differentially expressed protein spots, several defense-related proteins such as molecular chaperones and ROS-detoxifying enzymes were identified. The expression of 6 candidate proteins was investigated at the transcript level by Reverse Transcription Quantitative PCR (RT-qPCR). In silico, a highly-expressed uncharacterized protein LOC110648447 found in rubber trees was predicted to be a protein in the pathogenesis-related protein 10 (PR-10) class. In silico promoter analysis and structural-related characterization of this novel PR-10 protein suggest that it plays a potential role in defending rubber trees against R. microporus infection. The promoter contains WRKY-, MYB-, and other defense-related cis-acting elements. The structural model of the novel PR-10 protein predicted by I-TASSER showed a topology of the Bet v 1 protein family, including a conserved active site and a ligand-binding hydrophobic cavity.

CONCLUSIONS

A novel protein in the PR-10 group increased sharply in rubber tree leaves during interaction with the white root rot pathogen, potentially contributing to host defense. The results of this study provide information useful for white root rot disease management of rubber trees in the future.

Systematic analysis and expression of Gossypium 2ODD superfamily highlight the roles of GhLDOXs responding to alkali and other abiotic stress in cotton

BACKGROUND

2-oxoglutarate-dependent dioxygenase (2ODD) is the second largest family of oxidases involved in various oxygenation/hydroxylation reactions in plants. Many members in the family regulate gene transcription, nucleic acid modification/repair and secondary metabolic synthesis. The 2ODD family genes also function in the formation of abundant flavonoids during anthocyanin synthesis, thereby modulating plant development and response to diverse stresses.

RESULTS

Totally, 379, 336, 205, and 204 2ODD genes were identified in G. barbadense (Gb), G. hirsutum (Gh), G. arboreum (Ga), and G. raimondii (Gb), respectively. The 336 2ODDs in G. hirsutum were divided into 15 subfamilies according to their putative functions. The structural features and functions of the 2ODD members in the same subfamily were similar and evolutionarily conserved. Tandem duplications and segmental duplications served essential roles in the large-scale expansion of the cotton 2ODD family. Ka/Ks values for most of the gene pairs were less than 1, indicating that 2ODD genes undergo strong purifying selection during evolution. Gh2ODDs might act in cotton responses to different abiotic stresses. GhLDOX3 and GhLDOX7, two members of the GhLDOX subfamily from Gh2ODDs, were significantly down-regulated in transcription under alkaline stress. Moreover, the expression of GhLDOX3 in leaves was significantly higher than that in other tissues. These results will provide valuable information for further understanding the evolution mechanisms and functions of the cotton 2ODD genes in the future.

CONCLUSIONS

Genome-wide identification, structure, and evolution and expression analysis of 2ODD genes in Gossypium were carried out. The 2ODDs were highly conserved during evolutionary. Most Gh2ODDs were involved in the regulation of cotton responses to multiple abiotic stresses including salt, drought, hot, cold and alkali.

Engineering a norcoclaurine synthase for one-step synthesis of (S)-1-aryl-tetrahydroisoquinolines

Tetrahydroisoquinoline alkaloids (THIQAs) are ubiquitous compounds with important pharmaceutical and biological activity. Their key N-heterocyclic structural motifs are synthesised via Pictet-Spengler (P-S) reaction by norcoclaurine synthases (NCS) in plants. The synthesis of 1-aryl-tetrahydroisoquinoline alkaloids has attracted increasing attention due to their antitumor and antivirus activities. Herein, the L68T/M97V mutant of NCS from Thalictrum flavum with improved activity was developed by semi-rational design. This mutant not only showed higher catalytic performance (> 96% conversion) toward benzaldehyde and dopamine over the wild-type enzyme, but also catalysed the P-S reaction of the bulky substrate 4-biphenylaldehyde and dopamine with high conversion (> 99%) for the effective synthesis of 1-aryl-THIQA. In terms of stereoselectivity, all products synthesised by the L68T/M97V mutant showed high optical purity (92-99% enantiomeric excess).

Allergenicity and IgE Recognition of New Dau c 1 Allergens from Carrot

SCOPE

Carrot (Daucus carota) allergy is caused by the major carrot allergen Dau c 1, which is a mixture of several isoallergens and variants with sequence identities of >67% or >90%, respectively. However, little is known about the qualitative and quantitative composition of natural Dau c 1.

METHODS AND RESULTS

Mass spectrometry of isolated natural Dau c 1 reveals the existence of several yet unknown Dau c 1-like proteins. The study expresses four Dau c 1-like proteins in Escherichia coli. Two of the purified proteins, designated Dau c 1.0501 and 1.0601, exhibit sequence identities to Dau c 1.0101 and 1.0401 between 54% and 87%. They possess allergenic potential and are accepted as new isoallergens. One protein, designated as Dau c 1-like is >50% identical with the new isoallergens but exhibits no allergenicity. Sequence and structural comparisons of this protein with the known Dau c 1 isoallergens offer relevant clues about putative structural IgE epitopes.

CONCLUSION

Identification of new isoallergens and the identification of IgE epitopes may contribute to a more refined component resolved diagnosis and may lay ground for further epitope mapping and personalized targeted treatment approaches of carrot allergy in preclinical and clinical studies.

Characterization of benzylisoquinoline alkaloid methyltransferases in Liriodendron chinense provides insights into the phylogenic basis of angiosperm alkaloid diversity

Benzylisoquinoline alkaloids (BIAs) are a class of plant secondary metabolites with great pharmacological value. Their biosynthetic pathways have been extensively elucidated in the species from the Ranunculales order, such as poppy and Coptis japonica, in which methylation events play central roles and are directly responsible for BIA chemodiversity. Here, we combined BIA quantitative profiling and transcriptomic analyses to identify novel BIA methyltransferases (MTs) from Liriodendron chinense, a basal angiosperm plant. We identified an N-methyltransferase (LcNMT1) and two O-methyltransferases (LcOMT1 and LcOMT3), and characterized their biochemical functions in vitro. LcNMT1 methylates (S)-coclaurine to produce mono- and dimethylated products. Mutagenesis experiments revealed that a single-residue alteration is sufficient to change its substrate selectivity. LcOMT1 methylates (S)-norcoclaurine at the C6 site and LcOMT3 methylates (S)-coclaurine at the C7 site, respectively. Two key residues of LcOMT3, A115 and T301, are identified as important contributors to its catalytic activity. Compared with Ranunculales-derived NMTs, Magnoliales-derived NMTs were less abundant and had narrower substrate specificity, indicating that NMT expansion has contributed substantially to BIA chemodiversity in angiosperms, particularly in Ranunculales species. In summary, we not only characterized three novel enzymes that could be useful in the biosynthetic production of valuable BIAs but also shed light on the molecular origin of BIAs during angiosperm evolution.

Medicinal Plants: Guests and Hosts in the Heterologous Expression of High-Value Products

Medicinal plants play an important dual role in the context of the heterologous expression of high-value pharmaceutical products. On the one hand, the classical biochemical and modern omics approaches allowed for the discovery of various genes encoding biosynthetic pathways in medicinal plants. Recombinant DNA technology enabled introducing these genes and regulatory elements into host organisms and enhancing the heterologous production of the corresponding secondary metabolites. On the other hand, the transient expression of foreign DNA in plants facilitated the production of numerous proteins of pharmaceutical importance. This review summarizes several success stories of the engineering of plant metabolic pathways in heterologous hosts. Likewise, a few examples of recombinant protein expression in plants for therapeutic purposes are also highlighted. Therefore, the importance of medicinal plants has grown immensely as sources for valuable products of low and high molecular weight. The next step ahead for bioengineering is to achieve more success stories of industrial-scale production of secondary plant metabolites in microbial systems and to fully exploit plant cell factories' commercial potential for recombinant proteins.

Genome-Wide Transcriptomic Analysis of the Effects of Infection with the Hemibiotrophic Fungus Colletotrichum lindemuthianum on Common Bean

Bean anthracnose caused by the hemibiotrophic fungus Colletotrichum lindemuthianum is one of the most important diseases of common bean (Phaseolus vulgaris) in the world. In the present study, the whole transcriptome of common bean infected with C. lindemuthianum during compatible and incompatible interactions was characterized at 48 and 72 hpi, corresponding to the biotrophy phase of the infection cycle. Our results highlight the prominent role of pathogenesis-related (PR) genes from the PR10/Bet vI family as well as a complex interplay of different plant hormone pathways including Ethylene, Salicylic acid (SA) and Jasmonic acid pathways. Gene Ontology enrichment analysis reveals that infected common bean seedlings responded by down-regulation of photosynthesis, ubiquitination-mediated proteolysis and cell wall modifications. In infected common bean, SA biosynthesis seems to be based on the PAL pathway instead of the ICS pathway, contrarily to what is described in Arabidopsis. Interestingly, ~30 NLR were up-regulated in both contexts. Overall, our results suggest that the difference between the compatible and incompatible reaction is more a question of timing and strength, than a massive difference in differentially expressed genes between these two contexts. Finally, we used RT-qPCR to validate the expression patterns of several genes, and the results showed an excellent agreement with deep sequencing.

Phloem-specific localization of benzylisoquinoline alkaloid metabolism in opium poppy

Opium poppy is the only commercial source of the narcotic analgesics morphine and codeine, and semi-synthetic derivatives of the natural opiate precursor thebaine, including oxycodone and the opioid antagonist naloxone. The plant also accumulates the vasodilator and antitussive agents papaverine and noscapine, respectively, which together with morphine, codeine and thebaine comprise the major benzylisoquinoline alkaloids (BIAs) in opium poppy. A majority of enzymes involved in the highly branched BIA metabolism in opium poppy have now been discovered, with many specifically localized to sieve elements of the phloem based on immunofluorescence labeling techniques. Transcripts corresponding to sieve element-localized biosynthetic enzymes were detected in companion cells, as expected. The more recent application of shotgun proteomics has shown that several enzymes operating late in the morphine and noscapine biosynthetic pathways occur primarily in laticifers that are adjacent or proximal to sieve elements. BIA biosynthesis and accumulation in opium poppy involves three phloem cell types and implicates the translocation of key pathway intermediates between sieve elements and laticifers. The recent isolation of uptake transporters associated with laticifers supports an apoplastic rather than a symplastic route for translocation. In spite of the extensive elucidation of BIA biosynthetic enzymes in opium poppy, additional transporters and other auxiliary proteins are clearly necessary to support the complex spatial organization and dynamics involved in product formation and sequestration. In this review, we provide an update of BIA metabolism in opium poppy with a focus on the role of phloem in the biosynthesis of the major alkaloids.

A Bitter-Sweet Story: Unraveling the Genes Involved in Quinolizidine Alkaloid Synthesis in Lupinus albus

Alkaloids are part of a structurally diverse group of over 21,000 cyclic nitrogen-containing secondary metabolites that are found in over 20% of plant species. Lupinus albus are naturally containing quinolizidine alkaloid (QA) legumes, with wild accessions containing up to 11% of QA in seeds. Notwithstanding their clear advantages as a natural protecting system, lupin-breeding programs have selected against QA content without proper understanding of quinolizidine alkaloid biosynthetic pathway. This review summarizes the current status in this field, with focus on the utilization of natural mutations such as the one contained in pauper locus, and more recently the development of molecular markers, which along with the advent of sequencing technology, have facilitated the identification of candidate genes located in the pauper region. New insights for future research are provided, including the utilization of differentially expressed genes located on the pauper locus, as candidates for genome editing. Identification of the main genes involved in the biosynthesis of QA will enable precision breeding of low-alkaloid, high nutrition white lupin. This is important as plant based high quality protein for food and feed is an essential for sustainable agricultural productivity.

Transcriptome analysis of Leucojum aestivum and identification of genes involved in norbelladine biosynthesis

Transcriptome analysis of Leucojum aestivum led to the identification of 50 key genes associated with Amaryllidaceae alkaloid biosynthesis including norbelladine synthase which localized in the cytosol and catalyzed norbelladine formation. The Amaryllidaceae alkaloids (AAs) are a large group of plant specialized metabolites, which are known for their biological activities. Although the general chemical reactions in the AA biosynthetic pathway have been proposed, the genes and enzymes of the pathway remain largely unstudied. All AAs are synthesized from a common precursor, norbelladine, by the condensation of tyramine and 3,4-dihydroxybenzaldehyde. The enzyme norbelladine synthase (NBS) which catalyzes the condensation reaction has only been characterized at a molecular level from one species, and the subcellular localizations have not been explored. Hence, the intracellular compartments wherein the AAs are biosynthesized remain unknown. In this study, a first comprehensive transcriptomic analysis of summer snowflake (Leucojum aestivum) was done to identify key genes associated with AA biosynthesis. Fifty orthologous genes were identified and deposited into GenBank. In addition, we identified and further characterized NBS from the transcriptome of L. aestivum and previously reported Narcissus papyraceus. Phylogenetic analysis showed that LaNBS, NpNBS1 and NpNBS2 shared high amino acid identity. The heterologous expression of LaNBS produced a recombinant protein with NBS activity. Bioinformatic prediction and C-terminal GFP tagging in transiently transformed Nicotiana benthamiana showed that LaNBS, NpNBS1 and NpNBS2 were likely localized to the cytosol which suggests that the AA biosynthesis starts in the cytosol. This study provides an Amaryllidaceae transcriptome that will be very helpful to identify genes for characterization studies in AA metabolism in planta or using heterologous systems. In addition, our study will facilitate the bioengineering of AA biosynthetic pathway in plants or in microorganisms.

Jasmonate-Responsive Transcription Factors NnWRKY70a and NnWRKY70b Positively Regulate Benzylisoquinoline Alkaloid Biosynthesis in Lotus (Nelumbo nucifera)

Lotus (Nelumbo nucifera) is a large aquatic plant that accumulates pharmacologically significant benzylisoquinoline alkaloids (BIAs). However, little is known about their biosynthesis and regulation. Here, we show that the two group III WRKY transcription factors (TFs), NnWRKY70a and NnWRKY70b, positively regulate the BIA biosynthesis in lotus. Both NnWRKY70s are jasmonic acid (JA) responsive, with their expression profiles highly correlated to the BIA concentration and BIA pathway gene expression. A dual-luciferase assay showed that NnWRKY70a could transactivate the NnTYDC promoter, whereas NnWRKY70b could activate promoters of the three BIA structural genes, including NnTYDC, NnCYP80G, and Nn7OMT. In addition, the transient overexpression of NnWRKY70a and NnWRKY70b in lotus petals significantly elevated the BIA alkaloid concentrations. Notably, NnWRKY70b seems to be a stronger BIA biosynthesis regulator, because it dramatically induced more BIA structural gene expressions and BIA accumulation than NnWRKY70a. A yeast two-hybrid assay further revealed that NnWRKY70b physically interacted with NnJAZ1 and two other group III WRKY TFs (NnWRKY53b and NnWRKY70a), suggesting that it may cooperate with the other group III WRKYs to adjust the lotus BIA biosynthesis via the JA-signaling pathway. To illustrate the mechanism underlying NnWRKY70b-mediated BIA regulation in the lotus, a simplified model is proposed. Our study provides useful insights into the regulatory roles of WRKY TFs in the biosynthesis of secondary metabolites.

Chemoenzymatic One-Pot Process for the Synthesis of Tetrahydroisoquinolines

1,2,3,4-Tetrahydroisoquinolines form a valuable scaffold for a variety of bioactive secondary metabolites and commercial pharmaceuticals. Due to the harsh or complex conditions of the conventional chemical synthesis of this molecular motif, alternative mild reaction pathways are in demand. Here we present an easy-to-operate chemoenzymatic one-pot process for the synthesis of tetrahydroisoquinolines starting from benzylic alcohols and an amino alcohol. We initially demonstrate the oxidation of 12 benzylic alcohols by a laccase/TEMPO system to the corresponding aldehydes, which are subsequently integrated in a phosphate salt mediated Pictet–Spengler reaction with m-tyramine. The reaction conditions of both individual reactions were analyzed separately, adapted to each other, and a straightforward one-pot process was developed. This enables the production of 12 1,2,3,4-tetrahydroisoquinolines with yields of up to 87% with constant reaction conditions in phosphate buffer and common laboratory glass bottles without the supplementation of any additives.

New Trends and Future Opportunities in the Enzymatic Formation of C-C, C-N, and C-O bonds

Organic chemistry provides society with fundamental products we use daily. Concerns about the impact that the chemical industry has over the environment is propelling major changes in the way we manufacture chemicals. Biocatalysis offers an alternative to other synthetic approaches as it employs enzymes, Nature's catalysts, to carry out chemical transformations. Enzymes are biodegradable, come from renewable sources, operate under mild reaction conditions, and display high selectivities in the processes they catalyse. As a highly multidisciplinary field, biocatalysis benefits from advances in different areas, and developments in the fields of molecular biology, bioinformatics, and chemical engineering have accelerated the extension of the range of available transformations (E. L. Bell et al., Nat. Rev. Meth. Prim. 2021, 1, 1-21). Recently, we surveyed advances in the expansion of the scope of biocatalysis via enzyme discovery and protein engineering (J. R. Marshall et al., Tetrahedron 2021, 82, 131926). Herein, we focus on novel enzymes currently available to the broad synthetic community for the construction of new C-C, C-N and C-O bonds, with the purpose of providing the non-specialist with new and alternative tools for chiral and sustainable chemical synthesis.

Functional characterization of (S)-N-methylcoclaurine 3'-hydroxylase (NMCH) involved in the biosynthesis of benzylisoquinoline alkaloids in Corydalis yanhusuo

Benzylisoquinoline alkaloids (BIAs) are compounds naturally found in plants and can have significant value in clinical settings. Metabolic engineering and synthetic biology are both promising approaches for the heterologous acquisition of benzylisoquinoline alkaloids. (S)-N-methylcoclaurine 3'-hydroxylase (NMCH), a member of the CYP80 family of CYP450, is the penultimate catalytic enzyme that forms the central branch-point intermediate (S)-reticuline and plays a key role in the biosynthesis of BIAs. In this study, an NMCH gene was cloned from Corydalis yanhusuo, while in vitro reactions demonstrated that CyNMCH can catalyze (S)-N-methylcoclaurine to produce (S)-3'-hydroxy-N-methylcoclaurine. The Km and Kcat of CyNMCH were estimated and compared with those identified in Eschscholzia californica and Coptis japonica. This newly discovered CyNMCH will provide alternative genetic resources for the synthetic biological production of benzylisoquinoline alkaloids and provides a foundation to help analyze the biosynthetic pathway of BIAs biosynthesis in C. yanhusuo.

The molecular mechanism underlying pathogenicity inhibition by sanguinarine in Magnaporthe oryzae

BACKGROUND

Sanguinarine (SAN) is a benzophenanthridine alkaloid that broadly targets a range of pathways in mammalian and fungal cells. In this study we set out to explore the molecular mechanism of sanguinarine inhibition of the fungal development and pathogenicity of Magnaporthe oryzae with the hope that sanguinarine will bolster the development of antiblast agents.

RESULTS

We found that the fungus exhibited a significant reduction in vegetative growth and hyphal melanization while the spores produced long germ tubes on the artificial hydrophobic surface characteristic of a defect in thigmotropic sensing when exposed to 4, 8 and 0.5 μm sanguinarine, respectively. Consistent with these findings, we observed that the genes involved in melanin biosynthesis and the fungal hydrophobin MoMPG1 were remarkably suppressed in mycelia treated with 8 μm sanguinarine. Additionally, sanguinarine inhibited appressorium formation at a dose of 1.0 μm and this defect was restored by supplementing 5 mM of exogenous cAMP. By qRT-PCR assay we found cAMP pathway signalling genes such as MoCAP1 and MoCpkA were significantly repressed whereas MoCDTF1 and MoSOM1 were upregulated in sanguinarine-treated strains. Furthermore, we showed that sanguinarine does not selectively inhibit vegetative growth and appressorium formation of Guy11 but also other strains of M. oryzae. Finally, treatment of sanguinarine impaired the appressorium-mediated penetration and pathogenicity of M. oryzae in a dose-dependent manner.

CONCLUSION

Based on our results we concluded that sanguinarine is an attractive antimicrobial candidate for fungicide development in the control of rice blast disease. © 2021 Society of Chemical Industry.

A new minisatellite VNTR marker, Pscp1, discovered for the identification of opium poppy

Opium poppy, a member of the Papaveraceae family, is an ancient herbaceous plant and well-known medical resource in the pharmaceutical industry. However, opium poppies are grown worldwide for producing illicit drugs, significantly increasing the incidence of narcotic drug abuse. Since the narcotic poppy has not yet been genetically investigated, we characterized a novel variable number tandem repeat (VNTR) marker of forensically important poppy species based on the genetic analysis of 164 samples collected from two locations spanning the Jeolla province and Jeju island of South Korea. Comparing analysis of the chloroplast (cp) genome sequences for four representative species of Papaver (Papaver somniferum, Papaver somniferum subs. setigerum, Papaver orientale, and Papaver rhoeas) revealed a unique region with 1-3 repeats for 16 nucleotide motifs in the genome inverted repeat A (IRA, positions 128,651 to 128,698) region. For 16 nucleotide motifs, 3 repeats were found in P. somniferum, and 2 repeats were found in P. somniferum subs. setigerum. Therefore, 10 known and the 133 unknown, seized Papaver species were compared to determine whether the species could be identified via variations in the repeat units. The sizes of a novel VNTR ranged from 181 to 252 bp between the species. Phylogenetic analysis confirmed that a novel VNTR, which we named Pscp1, could clearly distinguish between the narcotic and non-narcotic types of Papaver species based on the patterns of sequence variation. Interestingly, we found that Pscp1 could also distinguish between P. somniferum and P. somniferum subs. setigerum. The regions of eight non-narcotic species displayed similar patterns and also differences were found due to the nucleotide substitution and deletion events. The structural differences of Pscp1 were observed within the two narcotic species or between the narcotic and non-narcotic species, suggesting that these variations may act as a genetic marker. We, therefore, developed a new Pscp1 PCR-capillary electrophoresis (CE) method that can reliably identify the narcotic type of Papaver species. Taken together, our findings suggest that the newly developed Pscp1 can be used as an identification marker of opium poppy, and establish that the Pscp1 genotyping method by PCR-CE is an effective primary screening tool that can also contribute to species discrimination in the field of forensic diagnosis and applications.

Development of Continuous Flow Systems to Access Secondary Amines Through Previously Incompatible Biocatalytic Cascades*

A key aim of biocatalysis is to mimic the ability of eukaryotic cells to carry out multistep cascades in a controlled and selective way. As biocatalytic cascades get more complex, reactions become unattainable under typical batch conditions. Here a number of continuous flow systems were used to overcome batch incompatibility, thus allowing for successful biocatalytic cascades. As proof-of-principle, reactive carbonyl intermediates were generated in situ using alcohol oxidases, then passed directly to a series of packed-bed modules containing different aminating biocatalysts which accordingly produced a range of structurally distinct amines. The method was expanded to employ a batch incompatible sequential amination cascade via an oxidase/transaminase/imine reductase sequence, introducing different amine reagents at each step without cross-reactivity. The combined approaches allowed for the biocatalytic synthesis of the natural product 4O-methylnorbelladine.

Development of Continuous Flow Systems to Access Secondary Amines Through Previously Incompatible Biocatalytic Cascades

A key aim of biocatalysis is to mimic the ability of eukaryotic cells to carry out multistep cascades in a controlled and selective way. As biocatalytic cascades get more complex, reactions become unattainable under typical batch conditions. Here a number of continuous flow systems were used to overcome batch incompatibility, thus allowing for successful biocatalytic cascades. As proof-of-principle, reactive carbonyl intermediates were generated in situ using alcohol oxidases, then passed directly to a series of packed-bed modules containing different aminating biocatalysts which accordingly produced a range of structurally distinct amines. The method was expanded to employ a batch incompatible sequential amination cascade via an oxidase/transaminase/imine reductase sequence, introducing different amine reagents at each step without cross-reactivity. The combined approaches allowed for the biocatalytic synthesis of the natural product 4O-methylnorbelladine.

Review: Biological functions of major latex-like proteins in plants

Major latex-like proteins (MLPs) have been identified in dicots and monocots. They are members of the birch pollen allergen Bet v 1 family as well as pathogenesis-related proteins class 10. MLPs have two main features. One is binding affinity toward various hydrophobic compounds, such as long-chain fatty acids, steroids, and systemic acquired resistance signals, via its internal hydrophobic cavity or hydrophobic residues on its surface. MLPs transport such compounds to other organs via phloem and xylem vessels and contribute to the expression of physiologically important ligands' activity in the particular organs. The second feature is responses to abiotic and biotic stresses. MLPs are involved in drought and salt tolerance through the mediation of plant hormone signaling pathways. MLPs generate resistance against pathogens by the induction of pathogenesis-related protein genes. Therefore, MLPs play crucial roles in drought and salt tolerance and resistance against pathogens. However, knowledge of MLPs is fragmented, and an overview of them is needed. Herein, we summarize the current knowledge of the biological functions of MLPs, which to our knowledge, is the first review about MLPs that has been reported.

Engineering Saccharomyces cerevisiae to produce plant benzylisoquinoline alkaloids

Benzylisoquinoline alkaloids (BIAs) are a diverse family of plant natural products with extensive pharmacological properties, but the yield of BIAs from plant is limited. The understanding of BIA biosynthetic mechanism in plant and the development of synthetic biology enable the possibility to produce BIAs through microbial fermentation, as an alternative to agriculture-based supply chains. In this review, we discussed the engineering strategies to synthesize BIAs in Saccharomyces cerevisiae (yeast) and improve BIA production level, including heterologous pathway reconstruction, enzyme engineering, expression regulation, host engineering and fermentation engineering. We also highlight recent metabolic engineering advances in the production of BIAs in yeast.

Peroxisome compartmentalization of a toxic enzyme improves alkaloid production

Eukaryotic cells compartmentalize metabolic pathways in organelles to achieve optimal reaction conditions and avoid crosstalk with cytosolic factors. We found that cytosolic expression of norcoclaurine synthase (NCS), the enzyme that catalyzes the first committed reaction in benzylisoquinoline alkaloid biosynthesis, is toxic in Saccharomyces cerevisiae and, consequently, restricts (S)-reticuline production. We developed a compartmentalization strategy that alleviates NCS toxicity while promoting increased (S)-reticuline titer. This strategy is achieved through efficient targeting of toxic NCS to the peroxisome while, crucially, taking advantage of the free flow of metabolite substrates and products across the peroxisome membrane. We demonstrate that expression of engineered transcription factors can mimic the oleate response for larger peroxisomes, further increasing benzylisoquinoline alkaloid titer without the requirement for peroxisome induction with fatty acids. This work specifically addresses the challenges associated with toxic NCS expression and, more broadly, highlights the potential for engineering organelles with desired characteristics for metabolic engineering.

PR10/Bet v1-like Proteins as Novel Contributors to Plant Biochemical Diversity

Pathogenesis-related (PR) proteins constitute a broad class of plant proteins with analogues found throughout nature from bacteria to higher eukaryotes. PR proteins were first noted in plants as part of the hypersensitive response, but have since been assigned an array of biological roles. The PR10/Bet v1-like proteins are a subset of PR proteins characterized by an ability to bind a wide range of lipophilic ligands, uniquely positioning them as contributors to specialized biosynthetic pathways. PR10/Bet v1-like proteins participate in the production of plant alkaloids and phenolics including flavonoids, both as general binding proteins and in special cases as catalysts. Owing initially to the perceived allergenic properties of PR10/Bet v1-like proteins, many were studied at the structural level to elucidate the basis for ligand binding. These studies provided a foundation for more recent efforts to understand higher-level structural order and how PR10/Bet v1-like proteins catalyse key reactions in plant pathways. Synthetic biology aimed at reconstituting plant-specialized metabolism in microorganisms uses knowledge of these proteins to fine-tune performance in new systems.

The scaffold-forming steps of plant alkaloid biosynthesis

Alkaloids from plants are characterised by structural diversity and bioactivity, and maintain a privileged position in both modern and traditional medicines. In recent years, there have been significant advances in elucidating the biosynthetic origins of plant alkaloids. In this review, I will describe the progress made in determining the metabolic origins of the so-called true alkaloids, specialised metabolites derived from amino acids containing a nitrogen heterocycle. By identifying key biosynthetic steps that feature in the majority of pathways, I highlight the key roles played by modifications to primary metabolism, iminium reactivity and spontaneous reactions in the molecular and evolutionary origins of these pathways.

Characterization of O-methyltransferases involved in the biosynthesis of tetrandrine in Stephania tetrandra

Tetrandrine is the most effective small molecule that has been found to inhibit the Ebola virus. It is a typical bisbenzylisoquinoline alkaloid and is the main active ingredient in Stephania tetrandra. Metabolic engineering and synthetic biology are potential methods for efficient and rapid acquisition of tetrandrine. S-adenosyl-L-methionine: (S)-norcoclaurine-6-O-methyltransferase (6OMT) is a rate-limiting step involved in the biosynthesis of tetrandrine. In this study, we identify S-adenosyl-L-methionine: (S)-norcoclaurine-6-O-methyltransferase from S. tetrandra, which catalyzes the conversion of (S)-norcoclaurine to (S)-coclaurine. Four 6OMT-like genes were cloned from S. tetrandra. An in vitro enzyme assay showed that St6OMT1 could catalyze the conversion of (S)-norcoclaurine to produce (S)-coclaurine. St6OMT2 can catalyze the production of very few (S)-coclaurine molecules, accompanied by more by-products with m/z 300, compared to St6OMT1. The newly discovered 6OMTs will provide an optional genetic component for benzylisoquinoline alkaloid (BIA) synthetic biology research. This work will lay the foundation for the analysis of the biosynthetic pathway of tetrandrine in S. tetrandra.

Over 100 Million Years of Enzyme Evolution Underpinning the Production of Morphine in the Papaveraceae Family of Flowering Plants

Phylogenomic analysis of whole genome sequences of five benzylisoquinoline alkaloid (BIA)-producing species from the Ranunculales and Proteales orders of flowering plants revealed the sequence and timing of evolutionary events leading to the diversification of these compounds. (S)-Reticuline is a pivotal intermediate in the synthesis of many BIAs and our analyses revealed parallel evolution between the two orders, which diverged ∼122 million years ago (MYA). Berberine is present in species across the entire Ranunculales, and we found co-evolution of genes essential for production of the protoberberine class. The benzophenanthridine class, which includes the antimicrobial compound sanguinarine, is specific to the Papaveraceae family of Ranunculales, and biosynthetic genes emerged after the split with the Ranunculaceae family ∼110 MYA but before the split of the three Papaveraceae species used in this study at ∼77 MYA. The phthalideisoquinoline noscapine and morphinan class of BIAs are exclusive to the opium poppy lineage. K_s estimation of paralogous pairs indicates that morphine biosynthesis evolved more recently than 18 MYA in the Papaver genus. In the preceding 100 million years gene duplication, neofunctionalization and recruitment of additional enzyme classes, combined with gene clustering, gene fusion, and gene amplification, resulted in emergence of medicinally valuable BIAs including morphine and noscapine.

Full-length transcriptome analysis of Coptis deltoidea and identification of putative genes involved in benzylisoquinoline alkaloids biosynthesis based on combined sequencing platforms

The study carry out comprehensive transcriptome analysis of C. deltoidea and exploration of BIAs biosynthesis and accumulation based on UHPLC-MS/MS and combined sequencing platforms. Coptis deltoidea is an important medicinal plant with a long history of medicinal use, which is rich in benzylisoquinoline alkaloids (BIAs). In this study, Ultra performance liquid chromatography-electrospray ionization tandem mass spectrometry (UHPLC-ESI-MS/MS) and combined sequencing platforms were performed for exploration of BIAs biosynthesis, accumulation and comprehensive transcriptome analysis of C. deltoidea. By metabolism profiling, the accumulation of ten BIAs was analyzed using UHPLC-MS/MS and different contents were observed in different organs. From transcriptome sequencing result, we applied single-molecule real-time (SMRT) sequencing to C. deltoidea and generated a total of 75,438 full-length transcripts. We proposed the candidate biosynthetic pathway of tyrosine, precursor of BIAs, and identified 64 full length-transcripts encoding enzymes putatively involved in BIAs biosynthesis. RNA-Seq data indicated that the majority of genes exhibited relatively high expression level in roots. Transport of BIAs was also important for their accumulation. Here, 9 ABC transporters and 2 MATE transporters highly homologous to known alkaloid transporters related with BIAs transport in roots and rhizomes were identified. These findings based on the combined sequencing platforms provide valuable genetic information for C. deltoidea and the results of transcriptome combined with metabolome analysis can help us better understand BIAs biosynthesis and transport in this medicinal plant. The information will be critical for further characterization of C. deltoidea transcriptome and molecular-assisted breeding for this medicinal plant with scarce resources.

Pictet-Spenglerases in alkaloid biosynthesis: Future applications in biocatalysis

Pictet-Spenglerases provide a key role in the biosynthesis of many biologically active alkaloids. There is increasing use of these biocatalysts as an alternative to traditional organic synthetic methods as they provide stereoselective and regioselective control under mild conditions. Products from these enzymes also contain privileged drug scaffolds (such as tetrahydroisoquinoline or β-carboline moieties), so there is interest in the characterization and use of these enzymes as versatile biocatalysts to synthesize analogs of the corresponding natural products for drug discovery. This review discusses all known Pictet-Spenglerase enzymes and their applications as biocatalysts.

Biosynthesis of plant tetrahydroisoquinoline alkaloids through an imine reductase route

Herein, we report a biocatalytic approach to synthesize plant tetrahydroisoquinoline alkaloids (THIQAs) from dihydroisoquinoline (DHIQ) precursors using imine reductases and N-methyltransferase (NMT). The imine reductase IR45 was engineered to significantly expand its substrate specificity, enabling efficient and stereoselective conversion of 1-phenyl and 1-benzyl 6,7-dimethoxy-DHIQs into the corresponding (S)-tetrahydroisoquinolines (S-THIQs). Coclaurine N-methyltransferase (CNMT) was able to further efficiently convert these (S)-THIQ intermediates into (S)-THIQAs. By assembling IRED, CNMT, and glucose dehydrogenase (GDH) in one reaction, we effectively constituted two artificial biosynthetic pathways in Escherichia coli and successfully applied them to the production of five (S)-THIQAs. This highly efficient (100% yield from DHIQs) and easily tailorable (adding other genes) biosynthetic approach will be useful for producing a variety of plant THIQAs.

Novel findings to the biosynthetic pathway of magnoflorine and taspine through transcriptomic and metabolomic analysis of Croton draco (Euphorbiaceae)

BACKGROUND

Croton draco is an arboreal species and its latex as well as some other parts of the plant, are traditionally used in the treatment of a wide range of ailments and diseases. Alkaloids, such as magnoflorine, prevent early atherosclerosis progression while taspine, an abundant constituent of latex, has been described as a wound-healer and antitumor-agent. Despite the great interest for these and other secondary metabolites, no omics resources existed for the species and the biosynthetic pathways of these alkaloids remain largely unknown.

RESULTS

To gain insights into the pathways involved in magnoflorine and taspine biosynthesis by C. draco and identify the key enzymes in these processes, we performed an integrated analysis of the transcriptome and metabolome in the major organs (roots, stem, leaves, inflorescences, and flowers) of this species. Transcript profiles were generated through high-throughput RNA-sequencing analysis while targeted and high resolution untargeted metabolomic profiling was also performed. The biosynthesis of these compounds appears to occur in the plant organs examined, but intermediaries may be translocated from the cells in which they are produced to other cells in which they accumulate.

CONCLUSIONS

Our results provide a framework to better understand magnoflorine and taspine biosynthesis in C. draco. In addition, we demonstrate the potential of multi-omics approaches to identify candidate genes involved in the biosynthetic pathways of interest.

Comparative analysis of the root and leaf transcriptomes in Chelidonium majus L

Chelidonium majus is a traditional medicinal plant, which commonly known as a rich resource for the major benzylisoquinoline alkaloids (BIAs), including morphine, sanguinarine, and berberine. To understand the biosynthesis of C. majus BIAs, we performed de novo transcriptome sequencing of its leaf and root tissues using Illumina technology. Following comprehensive evaluation of de novo transcriptome assemblies produced with five programs including Trinity, Bridger, BinPacker, IDBA-tran, and Velvet/Oases using a series of k-mer sizes (from 25 to 91), BinPacker was found to produce the best assembly using a k-mer of 25. This study reports the results of differential gene expression (DGE), functional annotation, gene ontology (GO) analysis, classification of transcription factor (TF)s, and SSR and miRNA discovery. Our DGE analysis identified 6,028 transcripts that were up-regulated in the leaf, and 4,722 transcripts that were up-regulated in the root. Further investigations showed that most of the genes involved in the BIA biosynthetic pathway are significantly expressed in the root compared to the leaf. GO analysis showed that the predominant GO domain is "cellular component", while TF analysis found bHLH to be the most highly represented TF family. Our study further identified 10 SSRs, out of a total of 39,841, that showed linkage to five unigenes encoding enzymes in the BIA pathway, and 10 conserved miRNAs that were previously not detected in this plant. The comprehensive transcriptome information presented herein provides a foundation for further explorations on study of the molecular mechanisms of BIA synthesis in C. majus.

Phosphorylation-dependent ribonuclease activity of Fra a 1 proteins

Abiotic and biotic stress situations cause the upregulation of the transcription of a number of plant defence genes. They code for so-called pathogenesis-related (PR) proteins such as PR proteins of class-10 (PR-10), whose biological functions are still unclear. PR10 proteins are members of the Bet v 1 (major birch pollen allergen) superfamily including related proteins from the cultivated strawberry Fragaria × ananassa (Fra a 1 proteins). Here, we analyzed the expression of 21 Fra a 1 genes in different tissues of the strawberry plant by quantitative real-time PCR. Thirteen members were mainly expressed in roots, three in stems, two in red fruits and leaves, and one in flowers. Five genes (Fra a 1.04-1.08) were selected based on their expression profiles, heterologously expressed in Escherichia coli, and their recombinant proteins functionally characterized. Ribonuclease activity, demonstrated by in-solution and in-gel RNA degradation assays, indicated complete hydrolysis of RNA only by Fra a 1.06. Moreover, phosphorylation assays showed that except for Fra a 1.06, the remaining four recombinant proteins were phosphorylated. Consequently, we investigated whether the phosphorylation status of the proteins affects their ribonuclease activity. Using an in-solution as well as an in-gel RNase activity assay, results demonstrated that the four recombinant proteins, dephosphorylated with phosphatases, exhibited ribonucleolytic activity against total RNA. Thus, the PR10 related proteins characterized in this study harbour a phosphorylation-dependent RNase activity. The results shed new light on the assumed function of PR10 proteins in plant defence.

Cloning and characterization of norbelladine synthase catalyzing the first committed reaction in Amaryllidaceae alkaloid biosynthesis

BACKGROUND

Amaryllidaceae alkaloids (AAs) are a large group of plant-specialized metabolites displaying an array of biological and pharmacological properties. Previous investigations on AA biosynthesis have revealed that all AAs share a common precursor, norbelladine, presumably synthesized by an enzyme catalyzing a Mannich reaction involving the condensation of tyramine and 3,4-dihydroxybenzaldehyde. Similar reactions have been reported. Specifically, norcoclaurine synthase (NCS) which catalyzes the condensation of dopamine and 4-hydroxyphenylacetaldehyde as the first step in benzylisoquinoline alkaloid biosynthesis.

RESULTS

With the availability of wild daffodil (Narcissus pseudonarcissus) database, a transcriptome-mining search was performed for NCS orthologs. A candidate gene sequence was identified and named norbelladine synthase (NBS). NpNBS encodes for a small protein of 19 kDa with an anticipated pI of 5.5. Phylogenetic analysis showed that NpNBS belongs to a unique clade of PR10/Bet v1 proteins and shared 41% amino acid identity to opium poppy NCS1. Expression of NpNBS cDNA in Escherichia coli produced a recombinant enzyme able to condense tyramine and 3,4-DHBA into norbelladine as determined by high-resolution tandem mass spectrometry.

CONCLUSIONS

Here, we describe a novel enzyme catalyzing the first committed step of AA biosynthesis, which will facilitate the establishment of metabolic engineering and synthetic biology platforms for the production of AAs.

A Highly Characterized Synthetic Landing Pad System for Precise Multicopy Gene Integration in Yeast

A fundamental undertaking of metabolic engineering involves identifying and troubleshooting metabolic bottlenecks that arise from imbalances in pathway flux. To expedite the systematic screening of enzyme orthologs in conjunction with DNA copy number tuning, here we develop a simple and highly characterized CRISPR-Cas9 integration system in Saccharomyces cerevisiae. Our engineering strategy introduces a series of synthetic DNA landing pads (LP) into the S. cerevisiae genome to act as sites for high-level gene integration. LPs facilitate multicopy gene integration of one, two, three, or four DNA copies in a single transformation, thus providing precise control of DNA copy number. We applied our LP system to norcoclaurine synthase (NCS), an enzyme with poor kinetic properties involved in the first committed step of the production of high-value benzylisoquinoline alkaloids. The platform enabled rapid construction of a 40-strain NCS library by integrating ten NCS orthologs in four gene copies each. Six active NCS variants were identified, whereby production of ( S)-norcoclaurine could be further enhanced by increasing NCS copy number. We anticipate the LP system will aid in metabolic engineering efforts by providing strict control of gene copy number and expediting strain and pathway engineering campaigns.

Benzylisoquinoline Alkaloids Biosynthesis in Sacred Lotus

Sacred lotus (Nelumbo nucifera Gaertn.) is an ancient aquatic plant used throughout Asia for its nutritional and medicinal properties. Benzylisoquinoline alkaloids (BIAs), mostly within the aporphine and bisbenzylisoquinoline structural categories, are among the main bioactive constituents in the plant. The alkaloids of sacred lotus exhibit promising anti-cancer, anti-arrhythmic, anti-HIV, and anti-malarial properties. Despite their pharmacological significance, BIA metabolism in this non-model plant has not been extensively investigated. In this review, we examine the diversity of BIAs in sacred lotus, with an emphasis on the distinctive stereochemistry of alkaloids found in this species. Additionally, we discuss our current understanding of the biosynthetic genes and enzymes involved in the formation of 1-benzylisoquinoline, aporphine, and bisbenzylisoquinoline alkaloids in the plant. We conclude that a comprehensive functional characterization of alkaloid biosynthetic enzymes using both in vitro and in vivo methods is required to advance our limited knowledge of BIA metabolism in the sacred lotus.

Characterization of the genetic factors affecting quinolizidine alkaloid biosynthesis and its response to abiotic stress in narrow-leafed lupin (Lupinus angustifolius L.)

Quinolizidine alkaloids (QAs) are toxic secondary metabolites that complicate the end use of narrow-leafed lupin (NLL; Lupinus angustifolius L.) grain, as levels sometimes exceed the industry limit for its use as a food and feed source. The genotypic and environmental influences on QA production in NLL are poorly understood. Here, the expression of QA biosynthetic genes was analysed in vegetative and reproductive tissues of bitter (high QA) and sweet (low QA) accessions. It was demonstrated that sweet accessions are characterized by lower QA biosynthetic gene expression exclusively in leaf and stem tissues than bitter NLL, consistent with the hypothesis that QAs are predominantly produced in aerial tissues and transported to seeds, rather than synthesized within the seed itself. This analysis informed our identification of additional candidate genes involved in QA biosynthesis. Drought and temperature stress are two major abiotic stresses that often occur during NLL pod set. Hence, we assessed the effect of drought, increased temperature, and their combination, on QA production in three sweet NLL cultivars. A cultivar-specific response to drought and temperature in grain QA levels was observed, including the identification of a cultivar where alkaloid levels did not change with these stress treatments.