Discovery of a Short-Chain Dehydrogenase from Catharanthus roseus that Produces a New Monoterpene Indole Alkaloid

Membrane protein Bcsdr2 mediates biofilm integrity, hyphal growth and virulence of Botrytis cinerea

Grey mould caused by Botrytis cinerea is a devastating disease responsible for large losses to agricultural production, and B. cinerea is a necrotrophic model fungal plant pathogen. Membrane proteins are important targets of fungicides and hotspots in the research and development of fungicide products. Wuyiencin affects the permeability and pathogenicity of B. cinerea, parallel reaction monitoring revealed the association of membrane protein Bcsdr2, and the bacteriostatic mechanism of wuyiencin was elucidated. In the present work, we generated and characterised ΔBcsdr2 deletion and complemented mutant B. cinerea strains. The ΔBcsdr2 deletion mutants exhibited biofilm loss and dissolution, and their functional activity was illustrated by reduced necrotic colonisation on strawberry and grape fruits. Targeted deletion of Bcsdr2 also blocked several phenotypic defects in aspects of mycelial growth, conidiation and virulence. All phenotypic defects were restored by targeted gene complementation. The roles of Bcsdr2 in biofilms and pathogenicity were also supported by quantitative real-time RT-PCR results showing that phosphatidylserine decarboxylase synthesis gene Bcpsd and chitin synthase gene BcCHSV II were downregulated in the early stages of infection for the ΔBcsdr2 strain. The results suggest that Bcsdr2 plays important roles in regulating various cellular processes in B. cinerea. KEY POINTS: • The mechanism of wuyiencin inhibits B. cinerea is closely associated with membrane proteins. • Wuyiencin can downregulate the expression of the membrane protein Bcsdr2 in B. cinerea. • Bcsdr2 is involved in regulating B. cinerea virulence, growth and development.

The Rauvolfia tetraphylla genome suggests multiple distinct biosynthetic routes for yohimbane monoterpene indole alkaloids

Monoterpene indole alkaloids (MIAs) are a structurally diverse family of specialized metabolites mainly produced in Gentianales to cope with environmental challenges. Due to their pharmacological properties, the biosynthetic modalities of several MIA types have been elucidated but not that of the yohimbanes. Here, we combine metabolomics, proteomics, transcriptomics and genome sequencing of Rauvolfia tetraphylla with machine learning to discover the unexpected multiple actors of this natural product synthesis. We identify a medium chain dehydrogenase/reductase (MDR) that produces a mixture of four diastereomers of yohimbanes including the well-known yohimbine and rauwolscine. In addition to this multifunctional yohimbane synthase (YOS), an MDR synthesizing mainly heteroyohimbanes and the short chain dehydrogenase vitrosamine synthase also display a yohimbane synthase side activity. Lastly, we establish that the combination of geissoschizine synthase with at least three other MDRs also produces a yohimbane mixture thus shedding light on the complex mechanisms evolved for the synthesis of these plant bioactives.

Isolation, purification and biochemical characterization of Conopomorpha cramerella farnesol dehydrogenase

In Southeast Asia, Conopomorpha cramerella (Snellen) which is commonly known as the cocoa pod borer (CPB) moth has been identified as the most detrimental pest of Theobroma cacao L. Apart from the various side effects on human health and non-target organisms, heavily relying on synthetic pyrethroid insecticides to control CPB infestations also increases the environmental contamination risks. Thus, developing biorational insecticides that minimally affect the non-target organism and environment by targeting the insect growth regulation process is needed to manage the pest population. In insects, juvenile hormones (JH) regulate critical biological events, especially metamorphosis, development and reproduction. Since the physiological roles of JH III vary among different organisms, the biochemical properties, especially substrate specificity and analogue inhibition, may also be different. Therefore, studies on the JH III biosynthetic pathway enzymes in both plants and insects are beneficial to discover more effective analogues. Bioinformatic analysis and biochemical characterization of a NADP⁺ -dependent farnesol dehydrogenase, an intermediate enzyme of the JH III pathway, from C. cramerella (CcFolDH), were described in this study. In addition, the farnesol analogues that may act as a potent analogue inhibitor for CcFolDH ware determined using in vitro enzymatic study. The phylogenetic analysis indicated that CcFolDH shared a close phylogenetic relationship to the honeybee's short-chain dehydrogenase/reductase. The 27 kDa CcFolDH has an NADP(H) binding domain with a typical Rossmann fold and is likely a homotetrameric protein in the solution. The enzyme had a greater preference for substrate trans, trans-farnesol and coenzyme NADP⁺ . In terms of analogue inhibitor inhibition, hexahydroxyfarnesyl acetone showed the highest inhibition (the lowest K_i ) compared to other farnesol analogues. Thus, hexahydroxyfarnesyl acetone would serve as the most potent active ingredient for future biorational pesticide management for C. cramerella infestation. Based on the bioinformatic analyses and biochemical characterizations conducted in this research, we proposed that rCcFolDH differs slightly from other reported farnesol dehydrogenases in terms of molecular weight, substrate preference, coenzymes utilization and analogue inhibitors selection.

Differential analysis of transcriptomic and metabolomic of free fatty acid rancidity process in oil palm (Elaeis guineensis) fruits of different husk types

INTRODUCTION

Oil palm is the world's highest yielding oil crop and its palm oil has high nutritional value, making it an oilseed plant with important economic value and application prospects. After picking, oil palm fruits exposed to air will gradually become soft and accelerate the process of fatty acid rancidity, which will not only affect their flavor and nutritional value, but also produce substances harmful to the human body. As a result, studying the dynamic change pattern of free fatty acids and important fatty acid metabolism-related regulatory genes during oil palm fatty acid rancidity can provide a theoretical basis for improving palm oil quality and extending its shelf life.

METHODS

The fruit of two shell types of oil palm, Pisifera (MP) and Tenera (MT), were used to study the changes of fruit souring at different times points of postharvesting, combined with LC-MS/MS metabolomics and RNA-seq transcriptomics techniques to analyze the dynamic changes of free fatty acids during fruit rancidity, and to find out the key enzyme genes and proteins in the process of free fatty acid synthesis and degradation according to metabolic pathways.

RESULTS AND DISCUSSION

Metabolomic study revealed that there were 9 different types of free fatty acids at 0 hours of postharvest, 12 different types of free fatty acids at 24 hours of postharvest, and 8 different types of free fatty acids at 36 hours of postharvest. Transcriptomic research revealed substantial changes in gene expression between the three harvest phases of MT and MP. Combined metabolomics and transcriptomics analysis results show that the expression of SDR, FATA, FATB and MFP four key enzyme genes and enzyme proteins in the rancidity of free fatty acids are significantly correlated with Palmitic acid, Stearic acid, Myristic acid and Palmitoleic acid in oil palm fruit. In terms of binding gene expression, the expression of FATA gene and MFP protein in MT and MP was consistent, and both were expressed higher in MP. FATB fluctuates unevenly in MT and MP, with the level of expression growing steadily in MT and decreasing in MP before increasing. The amount of SDR gene expression varies in opposite directions in both shell types. The above findings suggest that these four enzyme genes and enzyme proteins may play an important role in regulating fatty acid rancidity and are the key enzyme genes and enzyme proteins that cause differences in fatty acid rancidity between MT and MP and other fruit shell types. Additionally, differential metabolite and differentially expressed genes were present in the three postharvest times of MT and MP fruits, with the difference occurring 24 hours postharvest being the most notable. As a result, 24 hours postharvest revealed the most obvious difference in fatty acid tranquility between MT and MP shell types of oil palm. The results from this study offer a theoretical underpinning for the gene mining of fatty acid rancidity of various oil palm fruit shell types and the enhancement of oilseed palm acid-resistant germplasm cultivation using molecular biology methods.

Characterization of a putative tropinone reductase from Tarenaya hassleriana with a broad substrate specificity

A novel short-chain alcohol dehydrogenase from Tarenaya hassleriana labeled as putative tropinone reductase was heterologously expressed in Escherichia coli. Purified recombinant protein had molecular weight of approximately 30 kDa on 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis. T. hassleriana tropinone reductase-like enzyme (ThTRL) had not detected oxidative activity. The optimum pH for enzyme activity of ThTRL was weakly acidic (pH 5.0). 50°C was the optimum temperature for ThTRL. The highest catalytic efficiency and substrate affinity for recombinant ThTRL were observed with (+)-camphorquinone (k_cat /K_m  = 814.3 s^-1  mM^-1 , K_m  = 44.25 μM). ThTRL exhibited a broad substrate specificity and reduced various carbonyl compounds, including small lipophilic aldehydes and ketones, terpene ketones, and their structural analogs.

Genome-wide association study identifies variants of GhSAD1 conferring cold tolerance in cotton

Cold stress is a major environmental factor affecting plant growth and development. Although some plants have developed resistance to cold stress, the molecular mechanisms underlying this process are poorly understood. Using genome-wide association mapping with 200 cotton accessions collected from different regions, we identified variations in the short chain alcohol dehydrogenase gene, GhSAD1, that responds to cold stress. Virus-induced gene silencing and overexpression in Arabidopsis revealed that GhSAD1 fulfils important roles in cold stress responses. Ectopic expression of a haploid genotype of GhSAD1 (GhSAD1HapB) in Arabidopsis increased cold tolerance. Silencing of GhSAD1HapB resulted in a decrease in abscisic acid (ABA) content. Conversely, overexpression of GhSAD1HapB increased ABA content. GhSAD1HapB regulates cold stress responses in cotton through modulation of C-repeat binding factor activity, which regulates ABA signalling. GhSAD1HapB induces the expression of COLD-REGULATED (COR) genes and increases the amount of metabolites associated with cold stress tolerance. Overexpression of GhSAD1HapB partially complements the phenotype of the Arabidopsis ABA2 mutant, aba2-1. Collectively, these findings increase our understanding of the mechanisms underlying GhSAD1-mediated cold stress responses in cotton.

The crystal structure of the S154Y mutant carbonyl reductase from Leifsonia xyli explains enhanced activity for 3,5-Bis(trifluoromethyl)acetophenone reduction

Carbonyl reductase from Leifsonia xyli (LXCAR, UniProtKB - T2FLN4) can stereoselectively catalyze the reduction of 3,5-bis(trifluoromethyl)acetophenone (BTAP) to its corresponding alcohol, (R)-[3,5-bis(trifluoromethyl)phenyl]ethanol ((R)-BTPE), which is a valuable chiral intermediate for the synthesis of antiemetic drugs, Aprepitant and Fosaprepitant. Moreover, this protein was found to have a broad spectrum of substrate specificity and can asymmetrically catalyze the reduction of a variety of ketones and keto esters. Even though molecular modelling of this protein was done by Wang et al. (2014), a crystal structure has not yet obtained. In this study, a single mutant, S154Y, which was shown to have higher catalytic activity toward BTAP than that of the wild type, was overexpressed in Escherichia coli BL21 (DE3), purified, and crystallized. The crystal structure of LXCAR-S154Y explains how the mutant enzyme can work with BTAP more efficiently than wild type carbonyl reductase. Furthermore, the structure explains why LXCAR-S154Y can use either NADH or NADPH efficiently as a cofactor, as well as elucidates a proton relay system present in the enzyme.

Biosynthesis and synthetic biology of psychoactive natural products

Psychoactive natural products play an integral role in the modern world. The tremendous structural complexity displayed by such molecules confers diverse biological activities of significant medicinal value and sociocultural impact. Accordingly, in the last two centuries, immense effort has been devoted towards establishing how plants, animals, and fungi synthesize complex natural products from simple metabolic precursors. The recent explosion of genomics data and molecular biology tools has enabled the identification of genes encoding proteins that catalyze individual biosynthetic steps. Once fully elucidated, the "biosynthetic pathways" are often comparable to organic syntheses in elegance and yield. Additionally, the discovery of biosynthetic enzymes provides powerful catalysts which may be repurposed for synthetic biology applications, or implemented with chemoenzymatic synthetic approaches. In this review, we discuss the progress that has been made toward biosynthetic pathway elucidation amongst four classes of psychoactive natural products: hallucinogens, stimulants, cannabinoids, and opioids. Compounds of diverse biosynthetic origin - terpene, amino acid, polyketide - are identified, and notable mechanisms of key scaffold transforming steps are highlighted. We also provide a description of subsequent applications of the biosynthetic machinery, with an emphasis placed on the synthetic biology and metabolic engineering strategies enabling heterologous production.

Subfunctionalization of Paralog Transcription Factors Contributes to Regulation of Alkaloid Pathway Branch Choice in Catharanthus roseus

Catharanthus roseus produces a diverse range of specialized metabolites of the monoterpenoid indole alkaloid (MIA) class in a heavily branched pathway. Recent great progress in identification of MIA biosynthesis genes revealed that the different pathway branch genes are expressed in a highly cell type- and organ-specific and stress-dependent manner. This implies a complex control by specific transcription factors (TFs), only partly revealed today. We generated and mined a comprehensive compendium of publicly available C. roseus transcriptome data for MIA pathway branch-specific TFs. Functional analysis was performed through extensive comparative gene expression analysis and profiling of over 40 MIA metabolites in the C. roseus flower petal expression system. We identified additional members of the known BIS and ORCA regulators. Further detailed study of the ORCA TFs suggests subfunctionalization of ORCA paralogs in terms of target gene-specific regulation and synergistic activity with the central jasmonate response regulator MYC2. Moreover, we identified specific amino acid residues within the ORCA DNA-binding domains that contribute to the differential regulation of some MIA pathway branches. Our results advance our understanding of TF paralog specificity for which, despite the common occurrence of closely related paralogs in many species, comparative studies are scarce.

Purification, biochemical characterisation and bioinformatic analysis of recombinant farnesol dehydrogenase from Theobroma cacao

The juvenile hormones (JH) in plants are suggested to act as a form of plant defensive strategy especially against insect herbivory. The oxidation of farnesol to farnesoic acid is a key step in the juvenile hormone biosynthesis pathway. We herein present the purification and characterisation of the recombinant Theobroma cacao farnesol dehydrogenase enzyme that catalyses oxidation of farnesol to farnesal. The recombinant enzyme was purified to apparent homogeneity by affinity chromatography. The purified enzyme was characterised in terms of its deduced amino acid sequences, phylogeny, substrate specificity, kinetic parameters, structural modeling, and docking simulation. The phylogenetic analysis indicated that the T. cacao farnesol dehydrogenase (TcFolDH) showed a close relationship with A. thaliana farnesol dehydrogenase gene. The TcFolDH monomer had a large N-terminal domain which adopted a typical Rossmann-fold, harboring the GxxGxG motif (NADP(H)-binding domain) and a small C-terminal domain. The enzyme was a homotrimer comprised of subunits with molecular masses of 36 kDa. The TcFolDH was highly specific to NADP⁺ as coenzyme. The substrate specificity studies showed trans, trans-farnesol was the most preferred substrate for the TcFolDH, suggesting that the purified enzyme was a NADP⁺-dependent farnesol dehydrogenase. The docking of trans, trans-farnesol and NADP⁺ into the active site of the enzyme showed the important residues, and their interactions involved in the substrate and coenzyme binding of TcFolDH. Considering the extensive involvement of JH in both insects and plants, an in-depth knowledge on the recombinant production of intermediate enzymes of the JH biosynthesis pathway could help provide a potential method for insect control.

Short-Chain Dehydrogenase NcmD Is Responsible for the C-10 Oxidation of Nocamycin F in Nocamycin Biosynthesis

Nocamycins I and II, featured with a tetramic acid scaffold, were isolated from the broth of Saccharothrix syringae NRRL B-16468. The biosynthesis of nocamycin I require an intermediate bearing a hydroxyl group at the C-10 position. A short chain dehydrogenase/reductase NcmD was proposed to catalyze the conversion of the hydroxyl group to ketone at the C-10 position. By using the λ-RED recombination technology, we generated the NcmD deletion mutant strain S. syringae MoS-1005, which produced a new intermediate nocamycin F with a hydroxyl group at C-10 position. We then overexpressed NcmD in Escherichia coli BL21 (DE3), purified the His₆-tagged protein NcmD to homogeneity and conducted in vitro enzymatic assays. NcmD showed preference to the cofactor NAD⁺, and it effectively catalyzed the conversion from nocamyin F to nocamycin G, harboring a ketone group at C-10 position. However, NcmD showed no catalytic activity toward nocamyin II. NcmD achieved maximum catalytic activity at 45°C and pH 8.5. The kinetics of NcmD toward nocamycin F was investigated at 45°C, pH 8.5 in the presence of 2 mM NAD⁺. The K_m and k_cat values were 131 ± 13 μM and 65 ± 5 min⁻¹, respectively. In this study, we have characterized NcmD as a dehydrogenase, which is involved in forming the ketone group at the C-10 position of nocamycin F. The results provide new insights to the nocamycin biosynthetic pathway.

Crossing the Border: From Keto- to Imine Reduction in Short-Chain Dehydrogenases/Reductases

The family of NAD(P)H-dependent short-chain dehydrogenases/reductases (SDRs) comprises numerous biocatalysts capable of C=O or C=C reduction. The highly homologous noroxomaritidine reductase (NR) from Narcissus sp. aff. pseudonarcissus and Zt_SDR from Zephyranthes treatiae, however, are SDRs with an extended imine substrate scope. Comparison with a similar SDR from Asparagus officinalis (Ao_SDR) exhibiting keto-reducing activity, yet negligible imine-reducing capability, and mining the Short-Chain Dehydrogenase/Reductase Engineering Database indicated that NR and Zt_SDR possess a unique active-site composition among SDRs. Adapting the active site of Ao_SDR accordingly improved its imine-reducing capability. By applying the same strategy, an unrelated SDR from Methylobacterium sp. 77 (M77_SDR) with distinct keto-reducing activity was engineered into a promiscuous enzyme with imine-reducing activity, thereby confirming that the ability to reduce imines can be rationally introduced into members of the "classical" SDR enzyme family. Thus, members of the SDR family could be a promising starting point for protein approaches to generate new imine-reducing enzymes.

Crossing the Border: From Keto- to Imine Reduction in Short-Chain Dehydrogenases/Reductases

The family of NAD(P)H-dependent short-chain dehydrogenases/reductases (SDRs) comprises numerous biocatalysts capable of C=O or C=C reduction. The highly homologous noroxomaritidine reductase (NR) from Narcissus sp. aff. pseudonarcissus and Zt_SDR from Zephyranthes treatiae, however, are SDRs with an extended imine substrate scope. Comparison with a similar SDR from Asparagus officinalis (Ao_SDR) exhibiting keto-reducing activity, yet negligible imine-reducing capability, and mining the Short-Chain Dehydrogenase/Reductase Engineering Database indicated that NR and Zt_SDR possess a unique active-site composition among SDRs. Adapting the active site of Ao_SDR accordingly improved its imine-reducing capability. By applying the same strategy, an unrelated SDR from Methylobacterium sp. 77 (M77_SDR) with distinct keto-reducing activity was engineered into a promiscuous enzyme with imine-reducing activity, thereby confirming that the ability to reduce imines can be rationally introduced into members of the "classical" SDR enzyme family. Thus, members of the SDR family could be a promising starting point for protein approaches to generate new imine-reducing enzymes.

Whole-genome sequencing and analysis of the Chinese herbal plant Gelsemium elegans

BACKGROUND

Gelsemium elegans (G. elegans) (2n = 2x = 16) is genus of flowering plants belonging to the Gelsemicaeae family.

METHOD

Here, a high-quality genome assembly using the Oxford Nanopore Technologies (ONT) platform and high-throughput chromosome conformation capture techniques (Hi-C) were used.

RESULTS

A total of 56.11 Gb of raw GridION X5 platform ONT reads (6.23 Gb per cell) were generated. After filtering, 53.45 Gb of clean reads were obtained, giving 160 × coverage depth. The de novo genome assemblies 335.13 Mb, close to the 338 Mb estimated by k-mer analysis, was generated with contig N50 of 10.23 Mb. The vast majority (99.2%) of the G. elegans assembled sequence was anchored onto 8 pseudo-chromosomes. The genome completeness was then evaluated and 1338 of the 1440 conserved genes (92.9%) could be found in the assembly. Genome annotation revealed that 43.16% of the G. elegans genome is composed of repetitive elements and 23.9% is composed of long terminal repeat elements. We predicted 26,768 protein-coding genes, of which 84.56% were functionally annotated.

CONCLUSION

The genomic sequences of G. elegans could be a valuable source for comparative genomic analysis in the Gelsemicaeae family and will be useful for understanding the phylogenetic relationships of the indole alkaloid metabolism.

A Hedychium coronarium short chain alcohol dehydrogenase is a player in allo-ocimene biosynthesis

An enzyme is crucial for the formation of Hedychium coronarium scent and defense responses, which may be responsible for the biosynthesis of allo-ocimene in H. coronarium. Hedychium coronarium can emit a strong scent as its main scent constituents are monoterpenes and their derivatives. Among these derivatives, allo-ocimene is not only a very important volatile substance in flower aroma, but is also crucial to plant defense. However, the molecular mechanism of allo-ocimene biosynthesis has not been characterized in plants. In this study, a new alcohol dehydrogenase gene, HcADH, was cloned. The amino acid sequences encoded by HcADH contained the most conserved motifs of short chain alcohol dehydrogenase/reductases (SDRs), which included NAD⁺ binding domain, TGxxx[AG]xG and active site YxxxK. Real-time PCR analyses showed that the HcADH was highly expressed in the outer labellum but was almost undetectable in vegetative organs. The change in its expression level in petals was positively correlated with the emission pattern of allo-ocimene during flower development. HcADH expression coincides also the release level of allo-ocimene among different Hedychium species. Although HcADH is not expressed in the leaves, HcADH expression and allo-ocimene release in leaves can be induced by mechanical wounding or methyl jasmonate (MeJA) treatment. In addition, the expression of HcADH induced by mechanical wounding can be prevented by acetylsalicylic acid, a jasmonic acid biosynthesis inhibitor, suggesting that jasmonic acid might participate in the transmission of wounding signals. Using the Barley stripe mosaic virus (BSMV)-VIGS method, it was found that BSMV:HcADH₃₃₅ inoculation was able to down-regulate HcADH expression, decreasing only the release of allo-ocimene in flowers while the content of other volatile substances did not decrese. In vitro characterization showed that recombinant HcADH can catalyze geraniol into citral, and citral is an intermediate of allo-ocimene biosynthesis. HcADH may be responsible for the biosynthesis of allo-ocimene in H. coronarium, which is crucial for the formation of H. coronarium scent and defense function.

Exploiting the Catalytic Diversity of Short-Chain Dehydrogenases/Reductases: Versatile Enzymes from Plants with Extended Imine Substrate Scope

Numerous short-chain dehydrogenases/reductases (SDRs) have found biocatalytic applications in C=O and C=C (enone) reduction. For NADPH-dependent C=N reduction, imine reductases (IREDs) have primarily been investigated for extension of the substrate range. Here, we show that SDRs are also suitable for a broad range of imine reductions. The SDR noroxomaritidine reductase (NR) is involved in Amaryllidaceae alkaloid biosynthesis, serving as an enone reductase. We have characterized NR by using a set of typical imine substrates and established that the enzyme is active with all four tested imine compounds (up to 99 % conversion, up to 92 % ee). Remarkably, NR reduced two keto compounds as well, thus highlighting this enzyme family's versatility. Using NR as a template, we have identified an as yet unexplored SDR from the Amaryllidacea Zephyranthes treatiae with imine-reducing activity (≤95 % ee). Our results encourage the future characterization of SDR family members as a means of discovering new imine-reducing enzymes.

Discovery of a Short-Chain Dehydrogenase from Catharanthus roseus that Produces a New Monoterpene Indole Alkaloid

Plant monoterpene indole alkaloids, a large class of natural products, derive from the biosynthetic intermediate strictosidine aglycone. Strictosidine aglycone, which can exist as a variety of isomers, can be reduced to form numerous different structures. We have discovered a short-chain alcohol dehydrogenase (SDR) from plant producers of monoterpene indole alkaloids (Catharanthus roseus and Rauvolfia serpentina) that reduce strictosidine aglycone and produce an alkaloid that does not correspond to any previously reported compound. Here we report the structural characterization of this product, which we have named vitrosamine, as well as the crystal structure of the SDR. This discovery highlights the structural versatility of the strictosidine aglycone biosynthetic intermediate and expands the range of enzymatic reactions that SDRs can catalyse. This discovery further highlights how a sequence-based gene mining discovery approach in plants can reveal cryptic chemistry that would not be uncovered by classical natural product chemistry approaches.