Nicotiana benthamiana as a Transient Expression Host to Produce Auxin Analogs

A modular and synthetic biosynthesis platform for de novo production of diverse halogenated tryptophan-derived molecules

Halogen-containing molecules are ubiquitous in modern society and present unique chemical possibilities. As a whole, de novo fermentation and synthetic pathway construction for these molecules remain relatively underexplored and could unlock molecules with exciting new applications in industries ranging from textiles to agrochemicals to pharmaceuticals. Here, we report a mix-and-match co-culture platform to de novo generate a large array of halogenated tryptophan derivatives in Escherichia coli from glucose. First, we engineer E. coli to produce between 300 and 700 mg/L of six different halogenated tryptophan precursors. Second, we harness the native promiscuity of multiple downstream enzymes to access unexplored regions of metabolism. Finally, through modular co-culture fermentations, we demonstrate a plug-and-play bioproduction platform, culminating in the generation of 26 distinct halogenated molecules produced de novo including precursors to prodrugs 4-chloro- and 4-bromo-kynurenine and new-to-nature halogenated beta carbolines.

Plant Development in the Garden Pea as Revealed by Mutations in the Crd/PsYUC1 Gene

In common with other plant species, the garden pea (Pisum sativum) produces the auxin indole-3-acetic acid (IAA) from tryptophan via a single intermediate, indole-3-pyruvic acid (IPyA). IPyA is converted to IAA by PsYUC1, also known as Crispoid (Crd). Here, we extend our understanding of the developmental processes affected by the Crd gene by examining the phenotypic effects of crd gene mutations on leaves, flowers, and roots. We show that in pea, Crd/PsYUC1 is important for the initiation and identity of leaflets and tendrils, stamens, and lateral roots. We also report on aspects of auxin deactivation in pea.

An improved Nicotiana benthamiana bioproduction chassis provides novel insights into nicotine biosynthesis

The model plant Nicotiana benthamiana is an increasingly attractive organism for the production of high-value, biologically active molecules. However, N. benthamiana accumulates high levels of pyridine alkaloids, in particular nicotine, which complicates the downstream purification processes. Here, we report a new assembly of the N. benthamiana genome as well as the generation of low-nicotine lines by CRISPR/Cas9-based inactivation of berberine bridge enzyme-like proteins (BBLs). Triple as well as quintuple mutants accumulated three to four times less nicotine than the respective control lines. The availability of lines without functional BBLs allowed us to probe their catalytic role in nicotine biosynthesis, which has remained obscure. Notably, chiral analysis revealed that the enantiomeric purity of nicotine was fully lost in the quintuple mutants. In addition, precursor feeding experiments showed that these mutants cannot facilitate the specific loss of C6 hydrogen that characterizes natural nicotine biosynthesis. Our work delivers an improved N. benthamiana chassis for bioproduction and uncovers the crucial role of BBLs in the stereoselectivity of nicotine biosynthesis.

Molecular Farming of Pembrolizumab and Nivolumab

Immune checkpoint inhibitors (ICIs) are a class of immunotherapy agents capable of alleviating the immunosuppressive effects exerted by tumorigenic cells. The programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) immune checkpoint is one of the most ubiquitous checkpoints utilized by tumorigenic cells for immune evasion by inducing apoptosis and inhibiting the proliferation and cytokine production of T lymphocytes. Currently, the most frequently used ICIs targeting the PD-1/PD-L1 checkpoint include monoclonal antibodies (mAbs) pembrolizumab and nivolumab that bind to PD-1 on T lymphocytes and inhibit interaction with PD-L1 on tumorigenic cells. However, pembrolizumab and nivolumab are costly, and thus their accessibility is limited in low- and middle-income countries (LMICs). Therefore, it is essential to develop novel biomanufacturing platforms capable of reducing the cost of these two therapies. Molecular farming is one such platform utilizing plants for mAb production, and it has been demonstrated to be a rapid, low-cost, and scalable platform that can be potentially implemented in LMICs to diminish the exorbitant prices, ultimately leading to a significant reduction in cancer-related mortalities within these countries.

Plant synthetic biology: from inspiration to augmentation

Although it is still in its infancy, synthetic biology has the capacity to face scientific and societal problems related to modern agriculture. Innovations in cloning toolkits and genetic parts allow increased precision over gene expression in planta. We review the vast spectrum of available technologies providing a practical list of toolkits that take advantage of combinatorial power to introduce/alter metabolic pathways. We highlight that rational design is inspired by deep knowledge of natural and biochemical mechanisms. Finally, we provide several examples in which modern technologies have been applied to address these critical topics. Future applications in plants include not only pathway modifications but also prospects of augmenting plant anatomical features and developmental processes.

Plant-based engineering for production of high-valued natural products

Covering: up to March 2022Plants are a unique source of complex specialized metabolites, many of which play significant roles in human society. In many cases, however, the availability of these metabolites from naturally occurring sources fails to meet current demands. Thus, there is much interest in expanding the production capacity of target plant molecules. Traditionally, plant breeding, chemical synthesis, and microbial fermentation are considered the primary routes towards large scale production of natural products. Here, we explore the advances, challenges, and future of plant engineering as a complementary path. Although plants are an integral part of our food and agricultural systems and sustain an extensive array of chemical constituents, their complex genetics and physiology have prevented the optimal exploitation of plants as a production chassis. We highlight emerging engineering tools and scientific advances developed in recent years that have improved the prospects of using plants as a sustainable and scalable production platform. We also discuss technological limitations and overall economic outlook of plant-based production of natural products.

Directed Biosynthesis of New to Nature Alkaloids in a Heterologous Nicotiana benthamiana Expression Host

Plants produce a wide variety of pharmacologically active molecules classified as natural products. Derivatization of these natural products can modulate or improve the bioactivity of the parent compound. Unfortunately, chemical derivatization of natural products is often difficult or impractical. Here we use the newly discovered biosynthetic genes for two monoterpene indole alkaloids, alstonine and stemmadenine acetate, to generate analogs of these compounds. We reconstitute these biosynthetic genes in the heterologous host Nicotiana benthamiana along with an unnatural starting substrate to produce the corresponding new-to-nature alkaloid product.

Discovery and Characterization of Oxidative Enzymes Involved in Monoterpenoid Indole Alkaloid Biosynthesis

Monoterpene indole alkaloid (MIA) constitutes a structurally diverse plant natural product group with remarkable pharmacological activities. Many MIAs have been routinely used as potent drugs for several diseases, including leukemia (vinblastine), lung cancer (camptothecin), and malaria (quinine). Nevertheless, MIAs are biosynthesized at extremely low abundance in plants and, in many cases, require additional chemical functionalizations before their therapeutic uses. As oxygenations and oxidative rearrangements are critical throughout MIAs' structural scaffolding and modifications, the discovery and engineering of oxidative enzymes play essential roles in understanding and boosting the supplies of MIAs. Recent advances in omics technologies and synthetic biology have provided unprecedented amount of biochemical data and tools, paving a wide pathway for discovering, characterizing, and engineering enzymes involved in MIA biosynthesis. Here, we discuss the latest progress in understanding the roles of oxidative enzymes in MIA metabolism and describe a bioinformatic and biochemical pipeline to identify, characterize, and make use of these plant biocatalysts.

Transcriptomic evaluation on methyl bromide-induced phytotoxicity in Arabidopsis thaliana and its mode of phytotoxic action via the occurrence of reactive oxygen species and uneven distribution of auxin hormones

The increase in worldwide trade has caused the quality maintenance of commercialized agriproducts to be crucial in keeping its economic value. In recent years, methyl bromide (MB) has been used dominantly during quarantine and pre-shipment, despite it being an environmental hazard with global repercussions. Through this study, it was shown that Arabidopsis thaliana's 2 h exposure to the MB treatment displayed no signs of phytotoxicity, whereas its 4 h exposure significantly interfered with growth. The transcriptomic analysis found the molecular modifications in A. thaliana after the MB fumigation with the up-regulation of genes specifically relative to the abiotic and oxidative stress, and the down-regulation of auxin transporter genes. Some important gene expressions were verified by RT-qPCR and their expression patterns were similar. Oxidative stresses via the reactive oxygen species (ROS) in relation to MB phytotoxicity were confirmed with the increased malondialdehyde in MB-4h-treated A. thaliana. Uneven distribution of auxins via lower expression of auxin transporter genes was also determined using UPLC-ESI-QqQ MS. Application of two ROS scavengers such as N-acetyl-cysteine and L-glutathione minimized MB phytotoxic effect in A. thaliana. Therefore, MB caused severe oxidative stress, and alternatives regarding the use of MB should be considered.

Production of active human FGF21 using tobacco mosaic virus-based transient expression system

Fibroblast growth factor (FGF) family has a wide range of metabolic processes. FGF21 exerts critical physiological functions in clinical application. This study aimed to explore a convenient and highly efficient approach for rhFGF21 expression using TMV-TES. Firstly, the vector pTTEV-GFP was constructed, followed by optimisation of the expression parameters in Nicotiana benthamiana. Then, the rhFGF21 encoding gene harbouring vector pTTEV-rhFGF21 was constructed. Agrobacterium-mediated vacuum infiltration was performed with the optimised parameters and the expression of rhFGF21 was confirmed by the immunoblotting analysis. ELISA revealed that the protein accumulation of rhFGF21 accounts for 0.11% of total soluble proteins. The biological activity was evaluated and the results suggested that tobacco-expressed rhFGF21 could stimulate the glucose uptake in swiss 3T3-L1 adipocytes, which was similar to the activity of commercial products, suggesting its native biological activity. Therefore, using TMV-TES to express rhFGF21 will be a feasible approach for the mass production of rhFGF21.