Moss-made pharmaceuticals: from bench to bedside

Multifactorial analysis of terminator performance on heterologous gene expression in Physcomitrella

KEY MESSAGE

Characterization of Physcomitrella 3'UTRs across different promoters yields endogenous single and double terminators for usage in molecular pharming. The production of recombinant proteins for health applications accounts for a large share of the biopharmaceutical market. While many drugs are produced in microbial and mammalian systems, plants gain more attention as expression hosts to produce eukaryotic proteins. In particular, the good manufacturing practice (GMP)-compliant moss Physcomitrella (Physcomitrium patens) has outstanding features, such as excellent genetic amenability, reproducible bioreactor cultivation, and humanized protein glycosylation patterns. In this study, we selected and characterized novel terminators for their effects on heterologous gene expression. The Physcomitrella genome contains 53,346 unique 3'UTRs (untranslated regions) of which 7964 transcripts contain at least one intron. Over 91% of 3'UTRs exhibit more than one polyadenylation site, indicating the prevalence of alternative polyadenylation in Physcomitrella. Out of all 3'UTRs, 14 terminator candidates were selected and characterized via transient Dual-Luciferase assays, yielding a collection of endogenous terminators performing equally high as established heterologous terminators CaMV35S, AtHSP90, and NOS. High performing candidates were selected for testing as double terminators which impact reporter levels, dependent on terminator identity and positioning. Testing of 3'UTRs among the different promoters NOS, CaMV35S, and PpActin5 showed an increase of more than 1000-fold between promoters PpActin5 and NOS, whereas terminators increased reporter levels by less than tenfold, demonstrating the stronger effect promoters play as compared to terminators. Among selected terminator attributes, the number of polyadenylation sites as well as polyadenylation signals were found to influence terminator performance the most. Our results improve the biotechnology platform Physcomitrella and further our understanding of how terminators influence gene expression in plants in general.

Nature-inspired Enzyme engineering and sustainable catalysis: biochemical clues from the world of plants and extremophiles

The use of enzymes to accelerate chemical reactions for the synthesis of industrially important products is rapidly gaining popularity. Biocatalysis is an environment-friendly approach as it not only uses non-toxic, biodegradable, and renewable raw materials but also helps to reduce waste generation. In this context, enzymes from organisms living in extreme conditions (extremozymes) have been studied extensively and used in industries (food and pharmaceutical), agriculture, and molecular biology, as they are adapted to catalyze reactions withstanding harsh environmental conditions. Enzyme engineering plays a key role in integrating the structure-function insights from reference enzymes and their utilization for developing improvised catalysts. It helps to transform the enzymes to enhance their activity, stability, substrates-specificity, and substrate-versatility by suitably modifying enzyme structure, thereby creating new variants of the enzyme with improved physical and chemical properties. Here, we have illustrated the relatively less-tapped potentials of plant enzymes in general and their sub-class of extremozymes for industrial applications. Plants are exposed to a wide range of abiotic and biotic stresses due to their sessile nature, for which they have developed various mechanisms, including the production of stress-response enzymes. While extremozymes from microorganisms have been extensively studied, there are clear indications that plants and algae also produce extremophilic enzymes as their survival strategy, which may find industrial applications. Typical plant enzymes, such as ascorbate peroxidase, papain, carbonic anhydrase, glycoside hydrolases and others have been examined in this review with respect to their stress-tolerant features and further improvement via enzyme engineering. Some rare instances of plant-derived enzymes that point to greater exploration for industrial use have also been presented here. The overall implication is to utilize biochemical clues from the plant-based enzymes for robust, efficient, and substrate/reaction conditions-versatile scaffolds or reference leads for enzyme engineering.

Fabry Disease: Current and Novel Therapeutic Strategies. A Narrative Review

BACKGROUND

Fabry disease (FD) is an inherited lysosomal storage disorder, leading to multisystemic manifestations and causing significant morbidity and mortality.

OBJECTIVE

The aim of this narrative review is to present the current and novel therapeutic strategies in FD, including symptomatic and specific treatment options.

METHODS

A systematic literature search was conducted to identify relevant studies, including completed and ongoing randomized-controlled clinical trials (RCTs), prospective or retrospective cohort studies, case series and case reports that provided clinical data regarding FD treatment.

RESULTS

A multidisciplinary symptomatic treatment is recommended for FD patients, personalized according to disease manifestations and their severity. During the last two decades, FD-specific treatments, including two enzyme-replacement-therapies (agalsidase alfa and agalsidase beta) and chaperone treatment with migalastat have been approved for use and allowed for symptoms' stabilization or even disease burden reduction. More therapeutic agents are currently under investigation. Substrate reduction therapies, including lucerastat and venglustat, have shown promising results in RCTs and may be used either as monotherapy or as complementary therapy to established enzymereplacement- therapies. More stable enzyme-replacement-therapy molecules that are associated with less adverse events and lower likelihood of neutralizing antibodies formation have also been developed. Ex-vivo and in-vivo gene therapy is being tested in animal models and pilot human clinical trials, with preliminary results showing a favorable safety and efficacy profile.

CONCLUSION

The therapeutic landscape in FD appears to be actively expanding with more treatment options expected to become available in the near future, allowing for a more personalized approach in FD patients.

Optimising expression and extraction of recombinant proteins in plants

Recombinant proteins are of paramount importance for research, industrial and medical use. Numerous expression chassis are available for recombinant protein production, and while bacterial and mammalian cell cultures are the most widely used, recent developments have positioned transgenic plant chassis as viable and often preferential options. Plant chassis are easily maintained at low cost, are hugely scalable, and capable of producing large quantities of protein bearing complex post-translational modification. Several protein targets, including antibodies and vaccines against human disease, have been successfully produced in plants, highlighting the significant potential of plant chassis. The aim of this review is to act as a guide to producing recombinant protein in plants, discussing recent progress in the field and summarising the factors that must be considered when utilising plants as recombinant protein expression systems, with a focus on optimising recombinant protein expression at the genetic level, and the subsequent extraction and purification of target proteins, which can lead to substantial improvements in protein stability, yield and purity.

From Plant to Yeast-Advances in Biosynthesis of Artemisinin

Malaria is a life-threatening disease. Artemisinin-based combination therapy (ACT) is the preferred choice for malaria treatment recommended by the World Health Organization. At present, the main source of artemisinin is extracted from Artemisia annua; however, the artemisinin content in A. annua is only 0.1-1%, which cannot meet global demand. Meanwhile, the chemical synthesis of artemisinin has disadvantages such as complicated steps, high cost and low yield. Therefore, the application of the synthetic biology approach to produce artemisinin in vivo has magnificent prospects. In this review, the biosynthesis pathway of artemisinin was summarized. Then we discussed the advances in the heterologous biosynthesis of artemisinin using microorganisms (Escherichia coli and Saccharomyces cerevisiae) as chassis cells. With yeast as the cell factory, the production of artemisinin was transferred from plant to yeast. Through the optimization of the fermentation process, the yield of artemisinic acid reached 25 g/L, thereby producing the semi-synthesis of artemisinin. Moreover, we reviewed the genetic engineering in A. annua to improve the artemisinin content, which included overexpressing artemisinin biosynthesis pathway genes, blocking key genes in competitive pathways, and regulating the expression of transcription factors related to artemisinin biosynthesis. Finally, the research progress of artemisinin production in other plants (Nicotiana, Physcomitrella, etc.) was discussed. The current advances in artemisinin biosynthesis may help lay the foundation for the remarkable up-regulation of artemisinin production in A. annua through gene editing or molecular design breeding in the future.

Recombinant Spider Silk: Promises and Bottlenecks

Spider silk threads have exceptional mechanical properties such as toughness, elasticity and low density, which reach maximum values compared to other fibre materials. They are superior even compared to Kevlar and steel. These extraordinary properties stem from long length and specific protein structures. Spider silk proteins can consist of more than 20,000 amino acids. Polypeptide stretches account for more than 90% of the whole protein, and these domains can be repeated more than a hundred times. Each repeat unit has a specific function resulting in the final properties of the silk. These properties make them attractive for innovative material development for medical or technical products as well as cosmetics. However, with livestock breeding of spiders it is not possible to reach high volumes of silk due to the cannibalistic behaviour of these animals. In order to obtain spider silk proteins (spidroins) on a large scale, recombinant production is attempted in various expression systems such as plants, bacteria, yeasts, insects, silkworms, mammalian cells and animals. For viable large-scale production, cost-effective and efficient production systems are needed. This review describes the different types of spider silk, their proteins and structures and discusses the production of these difficult-to-express proteins in different host organisms with an emphasis on plant systems.

Unexpected Arabinosylation after Humanization of Plant Protein N-Glycosylation

As biopharmaceuticals, recombinant proteins have become indispensable tools in medicine. An increasing demand, not only in quantity but also in diversity, drives the constant development and improvement of production platforms. The N-glycosylation pattern on biopharmaceuticals plays an important role in activity, serum half-life and immunogenicity. Therefore, production platforms with tailored protein N-glycosylation are of great interest. Plant-based systems have already demonstrated their potential to produce pharmaceutically relevant recombinant proteins, although their N-glycan patterns differ from those in humans. Plants have shown great plasticity towards the manipulation of their glycosylation machinery, and some have already been glyco-engineered in order to avoid the attachment of plant-typical, putatively immunogenic sugar residues. This resulted in complex-type N-glycans with a core structure identical to the human one. Compared to humans, plants lack the ability to elongate these N-glycans with β1,4-linked galactoses and terminal sialic acids. However, these modifications, which require the activity of several mammalian enzymes, have already been achieved for Nicotiana benthamiana and the moss Physcomitrella. Here, we present the first step towards sialylation of recombinant glycoproteins in Physcomitrella, human β1,4-linked terminal N-glycan galactosylation, which was achieved by the introduction of a chimeric β1,4-galactosyltransferase (FTGT). This chimeric enzyme consists of the moss α1,4-fucosyltransferase transmembrane domain, fused to the catalytic domain of the human β1,4-galactosyltransferase. Stable FTGT expression led to the desired β1,4-galactosylation. However, additional pentoses of unknown identity were also observed. The nature of these pentoses was subsequently determined by Western blot and enzymatic digestion followed by mass spectrometric analysis and resulted in their identification as α-linked arabinoses. Since a pentosylation of β1,4-galactosylated N-glycans was reported earlier, e.g., on recombinant human erythropoietin produced in glyco-engineered Nicotiana tabacum, this phenomenon is of a more general importance for plant-based production platforms. Arabinoses, which are absent in humans, may prevent the full humanization of plant-derived products. Therefore, the identification of these pentoses as arabinoses is important as it creates the basis for their abolishment to ensure the production of safe biopharmaceuticals in plant-based systems.

Process Engineering of Biopharmaceutical Production in Moss Bioreactors via Model-Based Description and Evaluation of Phytohormone Impact

The moss Physcomitrella is an interesting production host for recombinant biopharmaceuticals. Here we produced MFHR1, a synthetic complement regulator which has been proposed for the treatment of diseases associated to the complement system as part of human innate immunity. We studied the impact of different operation modes for the production process in 5 L stirred-tank photobioreactors. The total amount of recombinant protein was doubled by using fed-batch or batch compared to semi-continuous operation, although the maximum specific productivity (mg MFHR1/g FW) increased just by 35%. We proposed an unstructured kinetic model which fits accurately with the experimental data in batch and semi-continuous operation under autotrophic conditions with 2% CO₂ enrichment. The model is able to predict recombinant protein production, nitrate uptake and biomass growth, which is useful for process control and optimization. We investigated strategies to further increase MFHR1 production. While mixotrophic and heterotrophic conditions decreased the MFHR1-specific productivity compared to autotrophic conditions, addition of the phytohormone auxin (NAA, 10 µM) to the medium enhanced it by 470% in shaken flasks and up to 230% and 260%, in batch and fed-batch bioreactors, respectively. Supporting this finding, the auxin-synthesis inhibitor L-kynurenine (100 µM) decreased MFHR1 production significantly by 110% and 580% at day 7 and 18, respectively. Expression analysis revealed that the MFHR1 transgene, driven by the Physcomitrella actin5 (PpAct5) promoter, was upregulated 16 h after NAA addition and remained enhanced over the whole process, whereas the auxin-responsive gene PpIAA1A was upregulated within the first 2 hours, indicating that the effect of auxin on PpAct5 promoter-driven expression is indirect. Furthermore, the day of NAA supplementation was crucial, leading to an up to 8-fold increase of MFHR1-specific productivity (0.82 mg MFHR1/g fresh weight, 150 mg accumulated over 7 days) compared to the productivity reported previously. Our findings are likely to be applicable to other plant-based expression systems to increase biopharmaceutical production and yields.

Phytochemical and pharmacological investigation of the ethanol extract of Byttneria pilosa Roxb

Background

Traditionally, the herb Byttneria pilosa Roxb. is used for bone fractures, boils, scabies, rheumatalgia, snake bites, syphilis, elephantiasis, poisoning, and eye infection. Scientific reports suggest that it has significant anti-inflammatory, analgesic, anti-diarrheal, anxiolytic, locomotion, sedative and anti-obesity effects. This study aims at the investigation of the phytochemical and pharmacological properties of the ethanol extract of this herb.

Methods

Fresh whole plant was extracted with absolute ethanol. A preliminary phytochemical investigation was followed by the evaluation of thrombolytic, anti-inflammatory, and anti-nociceptive activities by applying human clotted blood lysis, egg albumin, and acetic acid-induced writhing models, respectively.

Results

Phytochemical investigation suggests that B. pilosa possesses alkaloids, flavonoids, glycosides, terpenoids, tannins, saponins, and reducing sugars. The extract exhibited clot lysis and anti-inflammatory effects in a concentration-dependent manner. B. pilosa extract at 250 and 500 mg/kg also showed significant (p < 0.05) dose-dependent anti-nociceptive activity in Swiss albino mice.

Conclusion

The B. pilosa ethanol extract contains many important secondary metabolites and has thrombolytic, anti-inflammatory, and anti-nociceptive activities. More research is necessary on this hopeful medicinal herb.

Integrating plant molecular farming and materials research for next-generation vaccines

Biologics - medications derived from a biological source - are increasingly used as pharmaceuticals, for example, as vaccines. Biologics are usually produced in bacterial, mammalian or insect cells. Alternatively, plant molecular farming, that is, the manufacture of biologics in plant cells, transgenic plants and algae, offers a cheaper and easily adaptable strategy for the production of biologics, in particular, in low-resource settings. In this Review, we discuss current vaccination challenges, such as cold chain requirements, and highlight how plant molecular farming in combination with advanced materials can be applied to address these challenges. The production of plant viruses and virus-based nanotechnologies in plants enables low-cost and regional fabrication of thermostable vaccines. We also highlight key new vaccine delivery technologies, including microneedle patches and material platforms for intranasal and oral delivery. Finally, we provide an outlook of future possibilities for plant molecular farming of next-generation vaccines and biologics.

Integrating plant molecular farming and materials research for next-generation vaccines

Biologics - medications derived from a biological source - are increasingly used as pharmaceuticals, for example, as vaccines. Biologics are usually produced in bacterial, mammalian or insect cells. Alternatively, plant molecular farming, that is, the manufacture of biologics in plant cells, transgenic plants and algae, offers a cheaper and easily adaptable strategy for the production of biologics, in particular, in low-resource settings. In this Review, we discuss current vaccination challenges, such as cold chain requirements, and highlight how plant molecular farming in combination with advanced materials can be applied to address these challenges. The production of plant viruses and virus-based nanotechnologies in plants enables low-cost and regional fabrication of thermostable vaccines. We also highlight key new vaccine delivery technologies, including microneedle patches and material platforms for intranasal and oral delivery. Finally, we provide an outlook of future possibilities for plant molecular farming of next-generation vaccines and biologics.

Plant cell cultures as heterologous bio-factories for secondary metabolite production

Synthetic biology has been developing rapidly in the last decade and is attracting increasing attention from many plant biologists. The production of high-value plant-specific secondary metabolites is, however, limited mostly to microbes. This is potentially problematic because of incorrect post-translational modification of proteins and differences in protein micro-compartmentalization, substrate availability, chaperone availability, product toxicity, and cytochrome p450 reductase enzymes. Unlike other heterologous systems, plant cells may be a promising alternative for the production of high-value metabolites. Several commercial plant suspension cell cultures from different plant species have been used successfully to produce valuable metabolites in a safe, low cost, and environmentally friendly manner. However, few metabolites are currently being biosynthesized using plant platforms, with the exception of the natural pigment anthocyanin. Both Arabidopsis thaliana and Nicotiana tabacum cell cultures can be developed by multiple gene transformations and CRISPR-Cas9 genome editing. Given that the introduction of heterologous biosynthetic pathways into Arabidopsis and N. tabacum is not widely used, the biosynthesis of foreign metabolites is currently limited; however, therein lies great potential. Here, we discuss the exemplary use of plant cell cultures and prospects for using A. thaliana and N. tabacum cell cultures to produce valuable plant-specific metabolites.

Expression of a human cDNA in moss results in spliced mRNAs and fragmentary protein isoforms

Production of biopharmaceuticals relies on the expression of mammalian cDNAs in host organisms. Here we show that the expression of a human cDNA in the moss Physcomitrium patens generates the expected full-length and four additional transcripts due to unexpected splicing. This mRNA splicing results in non-functional protein isoforms, cellular misallocation of the proteins and low product yields. We integrated these results together with the results of our analysis of all 32,926 protein-encoding Physcomitrella genes and their 87,533 annotated transcripts in a web application, physCO, for automatized optimization. A thus optimized cDNA results in about twelve times more protein, which correctly localizes to the ER. An analysis of codon preferences of different production hosts suggests that similar effects occur also in non-plant hosts. We anticipate that the use of our methodology will prevent so far undetected mRNA heterosplicing resulting in maximized functional protein amounts for basic biology and biotechnology.

Contemporary therapeutics and new drug developments for treatment of Fabry disease: a narrative review

Fabry disease (OMIM 301500) is an X-linked (Xq22.1) lysosomal storage disorder leading to a progressive multisystem disease with high variability in both genotype and phenotype expression. The pathophysiological origin is found in an enzyme deficiency of the α-galactosidase A (enzyme commission no. 3.2.1.22) leading to accumulation of globotriaosylceramides in all lysosome carrying tissue. Especially organ manifestations of the heart, kidneys and nervous system are of significant prognostic value and might complicate with Fabry-associated pain, young aged cryptogenic stroke, proteinuria, kidney failure, hypertrophic cardiomyopathy, heart failure, malign cardiac rhythm disturbances and eventually sudden cardiac death. Up to the introduction of the first enzyme replacement agent in 2001, patients faced the disease's natural course with no disease-specific therapies available. Today, two recombinant enzyme replacement agents (Fabrazyme^®, Sanofi Genzyme, Cambridge, MA, USA; Replagal^®, Takeda Pharmaceutical, Tokio, Japan) and one oral chaperone therapy (Migalastat^®, Amicus Therapeutics, USA) are available and well-established in daily clinical practice. Substrate reduction therapy, second-generation enzyme replacement agents and different gene therapy approaches are currently undergoing preclinical and clinical trial phases and aim to improve therapeutic success and long-term outcome of patients with Fabry disease. This narrative review summarizes the currently available therapeutic options and future perspectives in Fabry disease.

Transfection of Arctic Bryum sp. KMR5045 as a Model for Genetic Engineering of Cold-Tolerant Mosses

Mosses number about 13,000 species and are an important resource for the study of the plant evolution that occurred during terrestrial colonization by plants. Recently, the physiological and metabolic characteristics that distinguish mosses from terrestrial plants have received attention. In the Arctic, in particular, mosses developed their own distinct physiological features to adapt to the harsh environment. However, little is known about the molecular mechanisms by which Arctic mosses survive in extreme environments due to the lack of basic knowledge and tools such as genome sequences and genetic transfection methods. In this study, we report the axenic cultivation and transfection of Arctic Bryum sp. KMR5045, as a model for bioengineering of Arctic mosses. We also found that the inherent low-temperature tolerance of KMR5045 permitted it to maintain slow growth even at 2°C, while the model moss species Physcomitrium patens failed to grow at all, implying that KMR5045 is suitable for studies of cold-tolerance mechanisms. To achieve genetic transfection of KMR5045, some steps of the existing protocol for P. patens were modified. First, protoplasts were isolated using 1% driselase solution. Second, the appropriate antibiotic was identified and its concentration was optimized for the selection of transfectants. Third, the cell regeneration period before transfer to selection medium was extended to 9 days. As a result, KMR5045 transfectants were successfully obtained and confirmed transfection by detection of intracellular Citrine fluorescence derived from expression of a pAct5:Citrine transgene construct. This is the first report regarding the establishment of a genetic transfection method for an Arctic moss species belonging to the Bryaceae. The results of this study will contribute to understanding the function of genes involved in environmental adaptation and to application for production of useful metabolites derived from stress-tolerant mosses.

Plant Platforms for Efficient Heterologous Protein Production

Production of recombinant proteins is primarily established in cultures of mammalian, insect and bacterial cells. Concurrently, concept of using plants to produce high-value pharmaceuticals such as vaccines, antibodies, and dietary proteins have received worldwide attention. Newer technologies for plant transformation such as plastid engineering, agroinfiltration, magnifection, and deconstructed viral vectors have been used to enhance the protein production in plants along with the inherent advantage of speed, scale, and cost of production in plant systems. Production of therapeutic proteins in plants has now a more pragmatic approach when several plant-produced vaccines and antibodies successfully completed Phase I clinical trials in humans and were further scheduled for regulatory approvals to manufacture clinical grade products on a large scale which are safe, efficacious, and meet the quality standards. The main thrust of this review is to summarize the data accumulated over the last two decades and recent development and achievements of the plant derived therapeutics. It also attempts to discuss different strategies employed to increase the production so as to make plants more competitive with the established production systems in this industry.

Genomics-enabled analysis of specialized metabolism in bioenergy crops: current progress and challenges

Plants produce a staggering diversity of specialized small molecule metabolites that play vital roles in mediating environmental interactions and stress adaptation. This chemical diversity derives from dynamic biosynthetic pathway networks that are often species-specific and operate under tight spatiotemporal and environmental control. A growing divide between demand and environmental challenges in food and bioenergy crop production has intensified research on these complex metabolite networks and their contribution to crop fitness. High-throughput omics technologies provide access to ever-increasing data resources for investigating plant metabolism. However, the efficiency of using such system-wide data to decode the gene and enzyme functions controlling specialized metabolism has remained limited; due largely to the recalcitrance of many plants to genetic approaches and the lack of 'user-friendly' biochemical tools for studying the diverse enzyme classes involved in specialized metabolism. With emphasis on terpenoid metabolism in the bioenergy crop switchgrass as an example, this review aims to illustrate current advances and challenges in the application of DNA synthesis and synthetic biology tools for accelerating the functional discovery of genes, enzymes and pathways in plant specialized metabolism. These technologies have accelerated knowledge development on the biosynthesis and physiological roles of diverse metabolite networks across many ecologically and economically important plant species and can provide resources for application to precision breeding and natural product metabolic engineering.

Functional expression and characterization of cinnamic acid 4-hydroxylase from the hornwort Anthoceros agrestis in Physcomitrella patens

Cinnamic acid 4-hydroxylase from the hornwort Anthoceros agrestis (AaC4H) was functionally expressed in the moss Physcomitrella patens and characterized at biochemical and molecular levels. Cinnamic acid 4-hydroxylase (C4H), a cytochrome P450-dependent hydroxylase, catalyzes the formation of 4-coumaric acid (=4-hydroxycinnamic acid) from trans-cinnamic acid. In the hornwort Anthoceros agrestis (Aa), this enzyme is supposed to be involved in the biosynthesis of rosmarinic acid (a caffeic acid ester of 3-(3,4-dihydroxyphenyl)lactic acid) and other related compounds. The coding sequence of AaC4H (CYP73A260) was expressed in the moss Physcomitrella patens (Pp_AaC4H). Protein extracts from the transformed moss showed considerably increased C4H activity driven by NADPH:cytochrome P450 reductase of the moss. Since Physcomitrella has own putative cinnamic acid 4-hydroxylases, enzyme characterization was carried out in parallel with the untransformed Physcomitrella wild type (Pp_WT). Apparent K_m-values for cinnamic acid and NADPH were determined to be at 17.3 µM and 88.0 µM for Pp_AaC4H and 25.1 µM and 92.3 µM for Pp_WT, respectively. Expression levels of AaC4H as well as two Physcomitrella patens C4H isoforms were analyzed by quantitative real-time PCR. While PpC4H_1 displayed constantly low levels of expression during the whole 21-day culture period, AaC4H and PpC4H_2 increased their expression during the first 6-8 days of the culture period and then decreased again. This work describes the biochemical in vitro characterization of a cytochrome P450-dependent enzyme, namely C4H, heterologously expressed in the haploid model plant Physcomitrella patens.

Functional expression and characterization of cinnamic acid 4-hydroxylase from the hornwort Anthoceros agrestis in Physcomitrella patens

Cinnamic acid 4-hydroxylase from the hornwort Anthoceros agrestis (AaC4H) was functionally expressed in the moss Physcomitrella patens and characterized at biochemical and molecular levels. Cinnamic acid 4-hydroxylase (C4H), a cytochrome P450-dependent hydroxylase, catalyzes the formation of 4-coumaric acid (=4-hydroxycinnamic acid) from trans-cinnamic acid. In the hornwort Anthoceros agrestis (Aa), this enzyme is supposed to be involved in the biosynthesis of rosmarinic acid (a caffeic acid ester of 3-(3,4-dihydroxyphenyl)lactic acid) and other related compounds. The coding sequence of AaC4H (CYP73A260) was expressed in the moss Physcomitrella patens (Pp_AaC4H). Protein extracts from the transformed moss showed considerably increased C4H activity driven by NADPH:cytochrome P450 reductase of the moss. Since Physcomitrella has own putative cinnamic acid 4-hydroxylases, enzyme characterization was carried out in parallel with the untransformed Physcomitrella wild type (Pp_WT). Apparent K_m-values for cinnamic acid and NADPH were determined to be at 17.3 µM and 88.0 µM for Pp_AaC4H and 25.1 µM and 92.3 µM for Pp_WT, respectively. Expression levels of AaC4H as well as two Physcomitrella patens C4H isoforms were analyzed by quantitative real-time PCR. While PpC4H_1 displayed constantly low levels of expression during the whole 21-day culture period, AaC4H and PpC4H_2 increased their expression during the first 6-8 days of the culture period and then decreased again. This work describes the biochemical in vitro characterization of a cytochrome P450-dependent enzyme, namely C4H, heterologously expressed in the haploid model plant Physcomitrella patens.

Mosses: Versatile plants for biotechnological applications

Mosses have long been recognized as powerful experimental tools for the elucidation of complex processes in plant biology. Recent increases in the availability of sequenced genomes and mutant collections, the establishment of novel technologies for targeted mutagenesis, and the development of viable protocols for large-scale production in bioreactors are now transforming mosses into one of the most versatile tools for biotechnological applications. In the present review, we highlight the astonishing biotechnological potential of mosses and how these plants are being exploited for industrial, pharmaceutical, and environmental applications. We focus on the biological features that support their use as model organisms for basic and applied research, and how these are being leveraged to explore the biotechnological potential in an increasing number of species. Finally, we also provide an overview of the available moss cultivation protocols from an industrial perspective, offering insights into batch operations that are not yet well established or do not even exist in the literature. Our goal is to bolster the use of mosses as factories for the biosynthesis of molecules of interest and to show how these species can be harnessed for the generation of novel and commercially useful bioproducts.

Functional Characterization of Class I Trehalose Biosynthesis Genes in Physcomitrella patens

The function of trehalose metabolism in plants during growth and development has been extensively studied, mostly in the eudicot Arabidopsis thaliana. So far, however, not much is known about trehalose metabolism in the moss Physcomitrella patens. Here, we show that in P. patens, two active trehalose-6-phosphate synthase enzymes exist, PpTPS1 and PpTPS2. Expression of both enzymes in Saccharomyces cerevisiae can complement the glucose-growth defect of the yeast tps1∆ mutant. Truncation of N-terminal extension in PpTPS1 and PpTPS2 resulted in higher TPS activity and high trehalose levels, upon expression in yeast. Physcomitrella knockout plants were generated and analyzed in various conditions to functionally characterize these proteins. tps1∆ and tps2∆ knockouts displayed a lower amount of caulonema filaments and were significantly reduced in size of gametophores as compared to the wild type. These phenotypes were more pronounced in the tps1∆ tps2∆ mutant. Caulonema formation is induced by factors such as high energy and auxins. Only high amounts of supplied energy were able to induce caulonema filaments in the tps1∆ tps2∆ mutant. Furthermore, this mutant was less sensitive to auxins as NAA-induced caulonema development was arrested in the tps1∆ tps2∆ mutant. In contrast, formation of caulonema filaments is repressed by cytokinins. This effect was more severe in the tps1∆ and tps1∆ tps2∆ mutants. Our results demonstrate that PpTPS1 and PpTPS2 are essential for sensing and signaling sugars and plant hormones to monitor the balance between caulonema and chloronema development.

Valuable Fatty Acids in Bryophytes-Production, Biosynthesis, Analysis and Applications

Bryophytes (mosses, liverworts and hornworts) often produce high amounts of very long-chain polyunsaturated fatty acids (vl-PUFAs) including arachidonic acid (AA, 20:4 Δ5,8,11,14) and eicosapentaenoic acid (EPA, 20:5 Δ5,8,11,14,17). The presence of vl-PUFAs is common for marine organisms such as algae, but rarely found in higher plants. This could indicate that bryophytes did not lose their marine origin completely when they landed into the non-aqueous environment. Vl-PUFA, especially the omega-3 fatty acid EPA, is essential in human diet for its benefits on healthy brain development and inflammation modulation. Recent studies are committed to finding new sources of vl-PUFAs instead of fish and algae oil. In this review, we summarize the fatty acid compositions and contents in the previous studies, as well as the approaches for qualification and quantification. We also conclude different approaches to enhance AA and EPA productions including biotic and abiotic stresses.

Mosses in biotechnology

Biotechnological exploitation of mosses has several aspects, for example, the use of moss extracts or the whole plant for diverse industrial applications as well as their employment as production platforms for valuable metabolites or pharmaceutical proteins, especially using the genetically and developmentally best-characterised model moss Physcomitrella patens. Whole moss plants, in particular peat mosses (Sphagnum spec.), are useful for environmental approaches, biomonitoring of environmental pollution and CO₂-neutral 'farming' on rewetted bogs to combat climate change. In addition, the lifestyle of mosses suggests the evolution of genes necessary to cope with biotic and abiotic stress situations, which could be applied to crop plants, and their structural features bear an inspiring potential for biomimetics approaches.

Plant-Made Antibodies: Properties and Therapeutic Applications

BACKGROUND

A cost-effective plant platform for therapeutic monoclonal antibody production is both flexible and scalable. Plant cells have mechanisms for protein synthesis and posttranslational modification, including glycosylation, similar to those in animal cells. However, plants produce less complex and diverse Asn-attached glycans compared to animal cells and contain plant-specific residues. Nevertheless, plant-made antibodies (PMAbs) could be advantageous compared to those produced in animal cells due to the absence of a risk of contamination from nucleic acids or proteins of animal origin.

OBJECTIVE

In this review, the various platforms of PMAbs production are described, and the widely used transient expression system based on Agrobacterium-mediated delivery of genetic material into plant cells is discussed in detail.

RESULTS

We examined the features of and approaches to humanizing the Asn-linked glycan of PMAbs. The prospects for PMAbs in the prevention and treatment of human infectious diseases have been illustrated by promising results with PMAbs against human immunodeficiency virus, rotavirus infection, human respiratory syncytial virus, rabies, anthrax and Ebola virus. The pre-clinical and clinical trials of PMAbs against different types of cancer, including lymphoma and breast cancer, are addressed.

CONCLUSION

PMAb biosafety assessments in patients suggest that it has no side effects, although this does not completely remove concerns about the potential immunogenicity of some plant glycans in humans. Several PMAbs at various developmental stages have been proposed. Promise for the clinical use of PMAbs is aimed at the treatment of viral and bacterial infections as well as in anti-cancer treatment.

Pharmacokinetics, pharmacodynamics, and safety of moss-aGalactosidase A in patients with Fabry disease

Moss-aGalactosidase A (moss-aGal) is a moss-derived version of human α-galactosidase developed for enzyme replacement therapy in patients with Fabry disease. It exhibits a homogenous N-glycosylation profile with >90% mannose-terminated glycans. In contrast to mammalian cell produced α-galactosidase, moss-aGal does not rely on mannose-6-phosphate receptor mediated endocytosis but targets the mannose receptor for tissue uptake. We conducted a phase 1 clinical trial with moss-aGal in six patients with confirmed diagnosis of Fabry disease during a 28-day schedule. All patients received a single dose of 0.2 mg/kg moss-aGal by i.v.-infusion. Primary endpoints of the trial were safety and pharmacokinetics; secondary endpoints were pharmacodynamics by analyzing urine and plasma Gb3 and lyso-Gb3 concentrations. In all patients, the administered single dose was well tolerated. No safety issues were observed. Pharmacokinetic data revealed a stable nonlinear profile with a short plasma half-life of moss-aGal of 14 minutes. After one single dose of moss-aGal, urinary Gb3 concentrations decreased up to 23% 7 days and up to 60% 28 days post-dose. Plasma concentrations of lyso-Gb3 decreased by 3.8% and of Gb3 by 11% 28 days post-dose. These data reveal that a single dose of moss-aGal was safe, well tolerated, and led to a prolonged reduction of Gb3 excretion. As previously shown, moss-aGal is taken up via the mannose receptor, which is expressed on macrophages but also on endothelial and kidney cells. Thus, these data indicate that moss-aGal may target kidney cells. After these promising results, phase 2/3 clinical trials are in preparation.

Recombinant Production of MFHR1, A Novel Synthetic Multitarget Complement Inhibitor, in Moss Bioreactors

The human complement system is an important part of the immune system responsible for lysis and elimination of invading microorganisms and apoptotic body cells. Improper activation of the system due to deficiency, mutations, or autoantibodies of complement regulators, mainly factor H (FH) and FH-related proteins (FHRs), causes severe kidney and eye diseases. However, there is no recombinant FH therapeutic available on the market. The first successful recombinant production of FH was accomplished with the moss bioreactor, Physcomitrella patens. Recently, a synthetic regulator, MFHR1, was designed to generate a multitarget complement inhibitor that combines the activities of FH and the FH-related protein 1 (FHR1). The potential of MFHR1 was demonstrated in a proof-of-concept study with transiently transfected insect cells. Here, we present the stable production of recombinant glyco-engineered MFHR1 in the moss bioreactor. The key features of this system are precise genome engineering via homologous recombination, Good Manufacturing Practice-compliant production in photobioreactors, high batch-to-batch reproducibility, and product stability. Several potential biopharmaceuticals are being produced in this system. In some cases, these are even biobetters, i.e., the recombinant proteins produced in moss have a superior quality compared to their counterparts from mammalian systems as for example moss-made aGal, which successfully passed phase I clinical trials. Via mass spectrometry-based analysis of moss-produced MFHR1, we now prove the correct synthesis and modification of this glycoprotein with predominantly complex-type N-glycan attachment. Moss-produced MFHR1 exhibits cofactor and decay acceleration activities comparable to FH, and its mechanism of action on multiple levels within the alternative pathway of complement activation led to a strong inhibitory activity on the whole alternative pathway, which was higher than with the physiological regulator FH.

Critical Evaluation of Strategies for the Production of Blood Coagulation Factors in Plant-Based Systems

The use of plants as production platforms for pharmaceutical proteins has been on the rise for the past two decades. The first marketed plant-made pharmaceutical, taliglucerase alfa against Gaucher's disease produced in carrot cells by Pfizer/Protalix Biotherapeutics, was approved by the US Food and Drug Administration (FDA) in 2012. The advantages of plant systems are low cost and highly scalable biomass production compared to the fermentation systems, safety compared with other expression systems, as plant-based systems do not produce endotoxins, and the ability to perform complex eukaryotic post-translational modifications, e.g., N-glycosylation that can be further engineered to achieve humanized N-glycan structures. Although bleeding disorders affect only a small portion of the world population, costs of clotting factor concentrates impose a high financial burden on patients and healthcare systems. The majority of patients, ∼75% in the case of hemophilia, have no access to an adequate treatment. The necessity of large-scale and less expensive production of human blood coagulation factors, particularly factors associated with rare bleeding disorders, may be an important area for plant-based systems, as coagulation factors do not fit into the industry-favored production models. In this review, we explore previous studies on recombinant production of coagulation Factor II, VIII, IX, and XIII in different plant species. Production of bioactive FII and FIX in plants was not achieved yet due to complex post-translational modifications, including vitamin K-dependent γ-carboxylation and propeptide removal. Although plant-made FVIII and FXIII showed specific activities, there are no follow-up studies like pre-clinical/clinical trials. Significant progress has been achieved in oral delivery of bioencapsulated FVIII and FIX to induce immune tolerance in murine models of hemophilia A and B, resp. Potential strategies to overcome bottlenecks in the production systems are also addressed in this review.

Engineering modular diterpene biosynthetic pathways in Physcomitrella patens

Modular assembly and heterologous expression in the moss Physcomitrella patens of pairs of diterpene synthases results in accumulation of modern land plant diterpenoids. Physcomitrella patens is a representative of the ancient bryophyte plant lineage with a genome size of 511 Mb, dominant haploid life cycle and limited chemical and metabolic complexity. For these plants, exceptional capacity for genome editing through homologous recombination is met with recently demonstrated in vivo assembly of multiple heterologous DNA fragments. These traits earlier made P. patens an attractive choice as a biotechnological chassis for photosynthesis-driven production of recombinant peptides. The lack of diterpene gibberellic acid phytohormones in P. patens combined with the recent targeted disruption of the single bifunctional diterpene synthase yielded lines devoid of endogenous diterpenoid metabolites and well-suited for engineering of terpenoid production. Here, we mimicked the modular nature of diterpene biosynthetic pathways found in modern land plants by developing a flexible pipeline to install three combinations of class II and class I diterpene synthases in P. patens to access industrially relevant diterpene biomaterials. In addition to a well-established neutral locus for targeted integration, we also explored loci created by a class of Long Terminal Repeat Retrotransposon present at moderate number in the genome of P. patens. Assembly of the pathways and production of the enzymes from the neutral locus led to accumulation of diterpenes matching the reported activities in the angiosperm sources. In contrast, insights gained with the retrotransposon loci indicate their suitability for targeting, but reveal potentially inherent complications which may require adaptation of the experimental design.

Quantitative moss cell biology

Research on mosses has provided answers to many fundamental questions in the life sciences, with the model moss Physcomitrella patens spearheading the field. Recent breakthroughs in cell biology were obtained in the quantification of chlorophyll fluorescence, signalling via calcium waves, the creation of designer organelles, gene identification in cellular reprogramming, reproduction via motile sperm and egg cells, asymmetric cell division, visualization of the actin cytoskeleton, identification of genes responsible for the shift from 2D to 3D growth, the structure and importance of the cell wall, and in the live imaging and modelling of protein networks in general. Highly standardized growth conditions, simplicity of most moss tissues, and an outstandingly efficient gene editing facilitate quantitative moss cell biology.

Host Cell Proteome of Physcomitrella patens Harbors Proteases and Protease Inhibitors under Bioproduction Conditions

Host cell proteins are inevitable contaminants of biopharmaceuticals. Here, we performed detailed analyses of the host cell proteome of moss ( Physcomitrella patens) bioreactor supernatants using mass spectrometry and subsequent bioinformatics analysis. Distinguishing between the apparent secretome and intracellular contaminants, a complex extracellular proteolytic network including subtilisin-like proteases, metallo-proteases, and aspartic proteases was identified. Knockout of a subtilisin-like protease affected the overall extracellular proteolytic activity. Besides proteases, also secreted protease-inhibiting proteins such as serpins were identified. Further, we confirmed predicted cleavage sites of 40 endogenous signal peptides employing an N-terminomics approach. The present data provide novel aspects to optimize both product stability of recombinant biopharmaceuticals as well as their maturation along the secretory pathway. Data are available via ProteomeXchange with identifier PXD009517.

Physcomitrella patens, a versatile synthetic biology chassis

During three decades the moss Physcomitrella patens has been developed to a superb green cell factory with the first commercial products on the market. In the past three decades the moss P. patens has been developed from an obscure bryophyte to a model organism in basic biology, biotechnology, and synthetic biology. Some of the key features of this system include a wide range of Omics technologies, precise genome-engineering via homologous recombination with yeast-like efficiency, a certified good-manufacturing-practice production in bioreactors, successful upscaling to 500 L wave reactors, excellent homogeneity of protein products, superb product stability from batch-to-batch, and a reliable procedure for cryopreservation of cell lines in a master cell bank. About a dozen human proteins are being produced in P. patens as potential biopharmaceuticals, some of them are not only similar to their animal-produced counterparts, but are real biobetters with superior performance. A moss-made pharmaceutical successfully passed phase 1 clinical trials, a fragrant moss, and a cosmetic moss-product is already on the market, highlighting the economic potential of this synthetic biology chassis. Here, we focus on the features of mosses as versatile cell factories for synthetic biology and their impact on metabolic engineering.

Engineering Plants for the Future: Farming with Value-Added Harvest

Plants and their rich variety of natural compounds are used to maintain and to improve health since the earliest stages of civilization. Despite great advances in synthetic organic chemistry, one fourth of present-day drugs have still a botanical origin, and we are currently living a revival of interest in new pharmaceuticals from plant sources.

Modern biotechnology has defined the potential of plants to be systems able to manufacture not only molecules naturally occurring in plants but also newly engineered compounds, from small to complex protein molecules, which may originate even from non-plant sources. Among these compounds, pharmaceuticals such as vaccines, antibodies and other therapeutic or prophylactic entities can be listed. For this technology, the term plant molecular farming has been coined with reference to agricultural applications due to the use of crops as biofactories for the production of high-added value molecules. In this perspective, edible plants have also been thought as a tool to deliver by the oral route recombinant compounds of medical significance for new therapeutic strategies. Despite many hurdles in establishing regulatory paths for this “novel” biotechnology, plants as bioreactors deserve more attention when considering their intrinsic advantages, such as the quality and safety of the recombinant molecules that can be produced and their potential for large-scale and low-cost production, despite worrying issues (e.g. amplification and diffusion of transgenes) that are mainly addressed by regulations, if not already tackled by the plant-made products already commercialized. The huge benefits generated by these valuable products, synthesized through one of the safest, cheapest and most efficient method, speak for themselves.

Milestone for plant-based recombinant protein production for human health use was the approval in 2012 by the US Food and Drug Administration of plant-made taliglucerase alfa, a therapeutic enzyme for the treatment of Gaucher’s disease, synthesized in carrot suspension cultures by Protalix BioTherapeutics.

In this review, we will go through the various approaches and results for plant-based production of proteins and recent progress in the development of plant-made pharmaceuticals (PMPs) for the prevention and treatment of human diseases. An analysis on acceptance of these products by public opinion is also tempted.

Production of Plant Secondary Metabolites: Examples, Tips and Suggestions for Biotechnologists

Plants are sessile organisms and, in order to defend themselves against exogenous (a)biotic constraints, they synthesize an array of secondary metabolites which have important physiological and ecological effects. Plant secondary metabolites can be classified into four major classes: terpenoids, phenolic compounds, alkaloids and sulphur-containing compounds. These phytochemicals can be antimicrobial, act as attractants/repellents, or as deterrents against herbivores. The synthesis of such a rich variety of phytochemicals is also observed in undifferentiated plant cells under laboratory conditions and can be further induced with elicitors or by feeding precursors. In this review, we discuss the recent literature on the production of representatives of three plant secondary metabolite classes: artemisinin (a sesquiterpene), lignans (phenolic compounds) and caffeine (an alkaloid). Their respective production in well-known plants, i.e., Artemisia, Coffea arabica L., as well as neglected species, like the fibre-producing plant Urtica dioica L., will be surveyed. The production of artemisinin and caffeine in heterologous hosts will also be discussed. Additionally, metabolic engineering strategies to increase the bioactivity and stability of plant secondary metabolites will be surveyed, by focusing on glycosyltransferases (GTs). We end our review by proposing strategies to enhance the production of plant secondary metabolites in cell cultures by inducing cell wall modifications with chemicals/drugs, or with altered concentrations of the micronutrient boron and the quasi-essential element silicon.

RecQ Helicases Function in Development, DNA Repair, and Gene Targeting in Physcomitrella patens

RecQ DNA helicases are genome surveillance proteins found in all kingdoms of life. They are characterized best in humans, as mutations in RecQ genes lead to developmental abnormalities and diseases. To better understand RecQ functions in plants we concentrated on Arabidopsis thaliana and Physcomitrella patens, the model species predominantly used for studies on DNA repair and gene targeting. Phylogenetic analysis of the six P. patens RecQ genes revealed their orthologs in humans and plants. Because Arabidopsis and P. patens differ in their RecQ4 and RecQ6 genes, reporter and deletion moss mutants were generated and gene functions studied in reciprocal cross-species and cross-kingdom approaches. Both proteins can be found in meristematic moss tissues, although at low levels and with distinct expression patterns. PpRecQ4 is involved in embryogenesis and in subsequent development as demonstrated by sterility of ΔPpRecQ4 mutants and by morphological aberrations. Additionally, ΔPpRecQ4 displays an increased sensitivity to DNA damages and an increased rate of gene targeting. Therefore, we conclude that PpRecQ4 acts as a repressor of recombination. In contrast, PpRecQ6 is not obviously important for moss development or DNA repair but does function as a potent enhancer of gene targeting.

Platforms for Plant-Based Protein Production

Plant molecular farming depends on a diversity of plant systems for production of useful recombinant proteins. These proteins include protein biopolymers, industrial proteins and enzymes, and therapeutic proteins. Plant production systems include microalgae, cells, hairy roots, moss, and whole plants with both stable and transient expression. Production processes involve a narrowing diversity of bioreactors for cell, hairy root, microalgae, and moss cultivation. For whole plants, both field and automated greenhouse cultivation methods are used with products expressed and produced either in leaves or seeds. Many successful expression systems now exist for a variety of different products with a list of increasingly successful commercialized products. This chapter provides an overview and examples of the current state of plant-based production systems for different types of recombinant proteins.

Promoter Choice Impacts the Efficiency of Plant Glyco-Engineering

Glyco-modulation of therapeutic proteins produced in plants has shown great success. Plant-based expression platforms for tailored human-like N-glycosylation are based on the overexpression of foreign genes. However, drawbacks such as protein miss targeting, interference with endogenous glycosyltransferases, or with plant development hamper the widespread use of the technology. Here a technique that facilitates the generation of recombinant proteins with targeted N-glycosylation at high homogeneity is described. It is focused on the synthesis of human-type β1,4-galactosylation by the overexpression of the human β1,4-galactosyltransferase (GalT) in Nicotiana benthamiana. A GalT construct that targets the enzyme to the required late Golgi compartment (ST GalT) is transiently co-expressed with two pharmaceutically relevant glycoproteins. The impact of eight promoters driving the expression of ST GalT is evaluated by mass spectrometry (MS) -based analyses. It is shown that five promoters (amongst them high expressors) induce aberrant non-human glycosylation. In contrast, three promoters, considered as moderately active, regulate gene expression to levels leading to an improved efficiency of di-galactosylation (and subsequent sialylation) on the reporter proteins. The results point to the importance of promoter choice for optimizing glycan engineering processes.

A Review of Biotechnological Artemisinin Production in Plants

Malaria is still an eminent threat to major parts of the world population mainly in sub-Saharan Africa. Researchers around the world continuously seek novel solutions to either eliminate or treat the disease. Artemisinin, isolated from the Chinese medicinal herb Artemisia annua, is the active ingredient in artemisinin-based combination therapies used to treat the disease. However, naturally artemisinin is produced in small quantities, which leads to a shortage of global supply. Due to its complex structure, it is difficult chemically synthesize. Thus to date, A. annua remains as the main commercial source of artemisinin. Current advances in genetic and metabolic engineering drives to more diverse approaches and developments on improving in planta production of artemisinin, both in A. annua and in other plants. In this review, we describe efforts in bioengineering to obtain a higher production of artemisinin in A. annua and stable heterologous in planta systems. The current progress and advancements provides hope for significantly improved production in plants.

Towards designer organelles by subverting the peroxisomal import pathway

The development of ‘designer’ organelles could be a key strategy to enable foreign pathways to be efficiently controlled within eukaryotic biotechnology. A fundamental component of any such system will be the implementation of a bespoke protein import pathway that can selectively deliver constituent proteins to the new compartment in the presence of existing endogenous trafficking systems. Here we show that the protein–protein interactions that control the peroxisomal protein import pathway can be manipulated to create a pair of interacting partners that still support protein import in moss cells, but are orthogonal to the naturally occurring pathways. In addition to providing a valuable experimental tool to give new insights into peroxisomal protein import, the variant receptor-signal sequence pair forms the basis of a system in which normal peroxisomal function is downregulated and replaced with an alternative pathway, an essential first step in the creation of a designer organelle.

Designer organelles could allow the isolation of synthetic biological pathways from endogenous components of the host cell. Here the authors engineer a peroxisomal protein import pathway orthogonal to the naturally occurring system.

Stable Production of the Antimalarial Drug Artemisinin in the Moss Physcomitrella patens

Malaria is a real and constant danger to nearly half of the world's population of 7.4 billion people. In 2015, 212 million cases were reported along with 429,000 estimated deaths. The World Health Organization recommends artemisinin-based combinatorial therapies, and the artemisinin for this purpose is mainly isolated from the plant Artemisia annua. However, the plant supply of artemisinin is irregular, leading to fluctuation in prices. Here, we report the development of a simple, sustainable, and scalable production platform of artemisinin. The five genes involved in artemisinin biosynthesis were engineered into the moss Physcomitrella patens via direct in vivo assembly of multiple DNA fragments. In vivo biosynthesis of artemisinin was obtained without further modifications. A high initial production of 0.21 mg/g dry weight artemisinin was observed after only 3 days of cultivation. Our study shows that P. patens can be a sustainable and efficient production platform of artemisinin that without further modifications allow for industrial-scale production. A stable supply of artemisinin will lower the price of artemisinin-based treatments, hence become more affordable to the lower income communities most affected by malaria; an important step toward containment of this deadly disease threatening millions every year.

Human Alpha Galactosidases Transiently Produced in Nicotiana benthamiana Leaves: New Insights in Substrate Specificities with Relevance for Fabry Disease

Deficiency of α-galactosidase A (α-GAL) causes Fabry disease (FD), an X-linked storage disease of the glycosphingolipid globtriaosylcerammide (Gb3) in lysosomes of various cells and elevated plasma globotriaosylsphingosine (Lyso-Gb3) toxic for podocytes and nociceptive neurons. Enzyme replacement therapy is used to treat the disease, but clinical efficacy is limited in many male FD patients due to development of neutralizing antibodies (Ab). Therapeutic use of modified lysosomal α-N-acetyl-galactosaminidase (α-NAGAL) with increased α-galactosidase activity (α-NAGAL^EL) has therefore been suggested. We transiently produced in Nicotiana benthamiana leaves functional α-GAL, α-NAGAL, and α-NAGAL^EL enzymes for research purposes. All enzymes could be visualized with activity-based probes covalently binding in their catalytic pocket. Characterization of purified proteins indicated that α-NAGAL^EL is improved in activity toward artificial 4MU-α-galactopyranoside. Recombinant α-NAGAL^EL and α-NAGAL are not neutralized by Ab-positive FD serum tested and are more stable in human plasma than α-GAL. Both enzymes hydrolyze the lipid substrates Gb3 and Lyso-Gb3 accumulating in Fabry patients. The addition to FD sera of α-NAGAL^EL, and to a lesser extent that of α-NAGAL, results in a reduction of the toxic Lyso-Gb3. In conclusion, our study suggests that modified α-NAGAL^EL might reduce excessive Lyso-Gb3 in FD serum. This neo-enzyme can be produced in Nicotiana benthamiana and might be further developed for the treatment of FD aiming at reduction of circulating Lyso-Gb3.

CRISPR-Cas9-mediated efficient directed mutagenesis and RAD51-dependent and RAD51-independent gene targeting in the moss Physcomitrella patens

The ability to address the CRISPR-Cas9 nuclease complex to any target DNA using customizable single-guide RNAs has now permitted genome engineering in many species. Here, we report its first successful use in a nonvascular plant, the moss Physcomitrella patens. Single-guide RNAs (sgRNAs) were designed to target an endogenous reporter gene, PpAPT, whose inactivation confers resistance to 2-fluoroadenine. Transformation of moss protoplasts with these sgRNAs and the Cas9 coding sequence from Streptococcus pyogenes triggered mutagenesis at the PpAPT target in about 2% of the regenerated plants. Mainly, deletions were observed, most of them resulting from alternative end-joining (alt-EJ)-driven repair. We further demonstrate that, in the presence of a donor DNA sharing sequence homology with the PpAPT gene, most transgene integration events occur by homology-driven repair (HDR) at the target locus but also that Cas9-induced double-strand breaks are repaired with almost equal frequencies by mutagenic illegitimate recombination. Finally, we establish that a significant fraction of HDR-mediated gene targeting events (30%) is still possible in the absence of PpRAD51 protein, indicating that CRISPR-induced HDR is only partially mediated by the classical homologous recombination pathway.

Algal Cell Factories: Approaches, Applications, and Potentials

With the advent of modern biotechnology, microorganisms from diverse lineages have been used to produce bio-based feedstocks and bioactive compounds. Many of these compounds are currently commodities of interest, in a variety of markets and their utility warrants investigation into improving their production through strain development. In this review, we address the issue of strain improvement in a group of organisms with strong potential to be productive “cell factories”: the photosynthetic microalgae. Microalgae are a diverse group of phytoplankton, involving polyphyletic lineage such as green algae and diatoms that are commonly used in the industry. The photosynthetic microalgae have been under intense investigation recently for their ability to produce commercial compounds using only light, CO₂, and basic nutrients. However, their strain improvement is still a relatively recent area of work that is under development. Importantly, it is only through appropriate engineering methods that we may see the full biotechnological potential of microalgae come to fruition. Thus, in this review, we address past and present endeavors towards the aim of creating productive algal cell factories and describe possible advantageous future directions for the field.

Moss-Produced, Glycosylation-Optimized Human Factor H for Therapeutic Application in Complement Disorders

Genetic defects in complement regulatory proteins can lead to severe renal diseases, including atypical hemolytic uremic syndrome and C3 glomerulopathies, and age-related macular degeneration. The majority of the mutations found in patients with these diseases affect the glycoprotein complement factor H, the main regulator of the alternative pathway of complement activation. Therapeutic options are limited, and novel treatments, specifically those targeting alternative pathway activation, are highly desirable. Substitution with biologically active factor H could potentially treat a variety of diseases that involve increased alternative pathway activation, but no therapeutic factor H is commercially available. We recently reported the expression of full-length recombinant factor H in moss (Physcomitrella patens). Here, we present the production of an improved moss-derived recombinant human factor H devoid of potentially immunogenic plant-specific sugar residues on protein N-glycans, yielding approximately 1 mg purified moss-derived human factor H per liter of initial P. patens culture after a multistep purification process. This glycosylation-optimized factor H showed full in vitro complement regulatory activity similar to that of plasma-derived factor H and efficiently blocked LPS-induced alternative pathway activation and hemolysis induced by sera from patients with atypical hemolytic uremic syndrome. Furthermore, injection of moss-derived factor H reduced C3 deposition and increased serum C3 levels in a murine model of C3 glomerulopathy. Thus, we consider moss-produced recombinant human factor H a promising pharmaceutical product for therapeutic intervention in patients suffering from complement dysregulation.

Extending the biosynthetic repertoires of cyanobacteria and chloroplasts

Chloroplasts in plants and algae and photosynthetic microorganisms such as cyanobacteria are emerging hosts for sustainable production of valuable biochemicals, using only inorganic nutrients, water, CO2 and light as inputs. In the past decade, many bioengineering efforts have focused on metabolic engineering and synthetic biology in the chloroplast or in cyanobacteria for the production of fuels, chemicals and complex, high-value bioactive molecules. Biosynthesis of all these compounds can be performed in photosynthetic organelles/organisms by heterologous expression of the appropriate pathways, but this requires optimization of carbon flux and reducing power, and a thorough understanding of regulatory pathways. Secretion or storage of the compounds produced can be exploited for the isolation or confinement of the desired compounds. In this review, we explore the use of chloroplasts and cyanobacteria as biosynthetic compartments and hosts, and we estimate the levels of production to be expected from photosynthetic hosts in light of the fraction of electrons and carbon that can potentially be diverted from photosynthesis. The supply of reducing power, in the form of electrons derived from the photosynthetic light reactions, appears to be non-limiting, but redirection of the fixed carbon via precursor molecules presents a challenge. We also discuss the available synthetic biology tools and the need to expand the molecular toolbox to facilitate cellular reprogramming for increased production yields in both cyanobacteria and chloroplasts.

In vivo assembly of DNA-fragments in the moss, Physcomitrella patens

Direct assembly of multiple linear DNA fragments via homologous recombination, a phenomenon known as in vivo assembly or transformation associated recombination, is used in biotechnology to assemble DNA constructs ranging in size from a few kilobases to full synthetic microbial genomes. It has also enabled the complete replacement of eukaryotic chromosomes with heterologous DNA. The moss Physcomitrella patens, a non-vascular and spore producing land plant (Bryophyte), has a well-established capacity for homologous recombination. Here, we demonstrate the in vivo assembly of multiple DNA fragments in P. patens with three examples of effective genome editing: we (i) efficiently deleted a genomic locus for diterpenoid metabolism yielding a biosynthetic knockout, (ii) introduced a salt inducible promoter, and (iii) re-routed endogenous metabolism into the formation of amorphadiene, a precursor of high-value therapeutics. These proof-of-principle experiments pave the way for more complex and increasingly flexible approaches for large-scale metabolic engineering in plant biotechnology.

Identification of Targets and Interaction Partners of Arginyl-tRNA Protein Transferase in the Moss Physcomitrella patens

Protein arginylation is a posttranslational modification of both N-terminal amino acids of proteins and sidechain carboxylates and can be crucial for viability and physiology in higher eukaryotes. The lack of arginylation causes severe developmental defects in moss, affects the low oxygen response in Arabidopsis thaliana and is embryo lethal in Drosophila and in mice. Although several studies investigated impact and function of the responsible enzyme, the arginyl-tRNA protein transferase (ATE) in plants, identification of arginylated proteins by mass spectrometry was not hitherto achieved. In the present study, we report the identification of targets and interaction partners of ATE in the model plant Physcomitrella patens by mass spectrometry, employing two different immuno-affinity strategies and a recently established transgenic ATE:GUS reporter line (Schuessele et al., 2016 New Phytol. , DOI: 10.1111/nph.13656). Here we use a commercially available antibody against the fused reporter protein (β-glucuronidase) to pull down ATE and its interacting proteins and validate its in vivo interaction with a class I small heatshock protein via Förster resonance energy transfer (FRET). Additionally, we apply and modify a method that already successfully identified arginylated proteins from mouse proteomes by using custom-made antibodies specific for N-terminal arginine. As a result, we identify four arginylated proteins from Physcomitrella patens with high confidence.Data are available via ProteomeXchange with identifier PXD003228 and PXD003232.