Combined application of biochar and peatmoss for mitigation of drought stress in tobacco

Drought poses a significant ecological threat that limits the production of crops worldwide. The objective of this study to examine the impact of soil applied biochar (BC) and peatmoss (PM) on the morpho-biochemical and quality traits of tobacco plants under drought conditions. In the present experiment work, a pot trial was conducted with two levels of drought severity (~ well-watered 75 ± 5% field capacity) and severe drought stress (~ 35 ± 5% field capacity), two levels of peatmoss (PM) @ 5% [PM+ (with peatmoss) and PM- (without peatmoss)] and three levels of rice straw biochar (BC0 = no biochar; BC1 = 150 mg kg- 1; and BC2 = 300 mg kg- 1 of soil) in tobacco plants. The results indicate that drought conditions significantly impacted the performance of tobacco plants. However, the combined approach of BC and PM significantly improved the growth, biomass, and total chlorophyll content (27.94%) and carotenoids (32.00%) of tobacco. This study further revealed that the drought conditions decreased the production of lipid peroxidation and proline accumulation. But the synergistic approach of BC and PM application increased soluble sugars (17.63 and 12.20%), soluble protein (31.16 and 15.88%), decreased the proline accumulation (13.92 and 9.03%), and MDA content (16.40 and 8.62%) under control and drought stressed conditions, respectively. Furthermore, the combined approach of BC and PM also improved the leaf potassium content (19.02%) by limiting the chloride ions (33.33%) under drought stressed conditions. Altogether, the balanced application of PM and BC has significant potential as an effective approach and sustainable method to increase the tolerance of tobacco plants subjected to drought conditions. This research uniquely highlights the combined potential of PM and BC as an eco-friendly strategy to enhance plant resilience under drought conditions, offering new insights into sustainable agricultural practices.

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

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

Identification of Granatane Alkaloids from Duboisia myoporoides (Solanaceae) using Molecular Networking and Semisynthesis

The Solanaceae plant family contains at least 98 genera and over 2700 species. The Duboisia genus stands out for its ability to produce pyridine and tropane alkaloids, which are relatively poorly characterized at the phytochemical level. In this study, we analyzed dried leaves of Duboisia spp. using supercritical CO2 extraction and ultra-high-pressure liquid chromatography coupled to high-resolution tandem mass spectrometry, followed by feature-based molecular networking. Thirty-one known tropane alkaloids were putatively annotated, and the identity of six (atropine, scopolamine, anisodamine, aposcopolamine, apoatropine, and noratropine) were identified using reference standards. Two new granatane alkaloids connected in the molecular network were highlighted from Duboisia myoporoides, and their α-granatane tropate and α-granatane isovalerate structures were unambiguously established by semisynthesis.

A P450 superfamily member NtCYP82C4 promotes nicotine biosynthesis in Nicotiana tabacum

In plants, cytochrome P450s are monooxygenase that play key roles in the synthesis and degradation of intracellular substances. In tobacco, the majority of studies examining the P450 superfamily have concentrated on the CYP82E subfamily, where multiple family members function as demethylases, facilitating the synthesis of nornicotine. In this study, NtCYP82C4, a tobacco P450 superfamily member, was identified from a gene-edited tobacco mutant that nicotine biosynthesis in tobacco leaves is evidently reduced. Compared to the wild-type plants, the knockout of NtCYP82C4 resulted in a significantly lower nicotine content and biomass in tobacco leaves. Transcriptome and metabolome analyses indicated that the knockout of NtCYP82C4 inhibites secondary metabolic processes in tobacco plants, leading to the accumulation of some important precursors in the nicotine synthesis process, including aspartic acid and nicotinic acid, and increases nitrogen partitioning associated with those processes such as amino acid synthesis and utilization. It is speculated that NtCYP82C4 may function as an important catalase downstream of the nicotine synthesis. Currently, most of the steps and enzymes involved in the nicotine biosynthesis process in tobacco have been elucidated. Here, our study deepens the current understanding of nicotine biosynthesis process and provides new enzyme targets for nicotine synthesis in tobacco plants.

Secretory structures and histochemistry of roots, stem, and leaves of medicinal plant Fibraurea tinctoria Lour

Fibraurea tinctoria Lour. (Menispermaceae) is a medicinal plant used by many local tribes in Indonesia and other countries. This species has pharmacological potential, such as antimalaria, antibacterial, antitumor, antioxidant, anticancer, antidiabetic, anti-inflammatory, and hepato-protector. However, the secretory structures and sites of secondary metabolite accumulation still need to be studied. This study aimed to explore the secretory structures and reveal the accumulation sites of the main classes of secondary metabolites in the root, stem, and leaves of F. tinctoria. Histochemical analysis using various specific reagents was performed on freehand sections of the fresh organs to detect alkaloids, phenolics, terpenoids, and lipophilic compounds. Observations of secretory structures were carried out using light microscopy. The result showed that idioblast was the predominant secretory structure in the plant organs and contained all the chemical groups investigated, while laticifer accumulated alkaloids were found only in the stem. Some secondary metabolites were localized in the xylem, intercellular space, and cuticle layer. Crystals were observed in the root, stem, and leaf of this species. These results might be helpful as guide information for extracting the particular plant parts to obtain the desired secondary metabolites. It suggested that leaves are a potential alternative source of medicinal raw material of this species, in addition to the stem. RESEARCH HIGHLIGHTS: The first study on secretory structures of Fibraurea tinctoria. Secondary metabolites in F. tinctoria organs accumulate in specialized and unspecialized structures. The idioblast is the primary secretory structure in the organs of F. tinctoria spreading over the root, stem, and leaves.

An update on the formation in tobacco, toxicity and carcinogenicity of N'-nitrosonornicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

The tobacco-specific nitrosamines N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) are considered 'carcinogenic to humans' by the International Agency for Research on Cancer (IARC) and are believed to be important in the carcinogenic effects of both smokeless tobacco and combusted tobacco products. This short review focuses on the results of recent studies on the formation of NNN and NNK in tobacco, and their carcinogenicity and toxicity in laboratory animals. New mechanistic insights are presented regarding the role of dissimilatory nitrate reductases in certain microorganisms involved in the conversion of nitrate to nitrite that leads to the formation of NNN and NNK during curing and processing of tobacco. Carcinogenicity studies of the enantiomers of the major NNK metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and the enantiomers of NNN are reviewed. Recent toxicity studies of inhaled NNK and co-administration studies of NNK with formaldehyde, acetaldehyde, acrolein and CO2, all of which occur in high concentrations in cigarette smoke, are discussed.

A century of studying plant secondary metabolism-From "what?" to "where, how, and why?"

Over the past century, early advances in understanding the identity of the chemicals that collectively form a living plant have led scientists to deeper investigations exploring where these molecules localize, how they are made, and why they are synthesized in the first place. Many small molecules are specific to the plant kingdom and have been termed plant secondary metabolites, despite the fact that they can play primary and essential roles in plant structure, development, and response to the environment. The past 100 yr have witnessed elucidation of the structure, function, localization, and biosynthesis of selected plant secondary metabolites. Nevertheless, many mysteries remain about the vast diversity of chemicals produced by plants and their roles in plant biology. From early work characterizing unpurified plant extracts, to modern integration of 'omics technology to discover genes in metabolite biosynthesis and perception, research in plant (bio)chemistry has produced knowledge with substantial benefits for society, including human medicine and agricultural biotechnology. Here, we review the history of this work and offer suggestions for future areas of exploration. We also highlight some of the recently developed technologies that are leading to ongoing research advances.

Reliable biological indicator identification and evaluation of tobacco-derived nicotine using an ultra-sensitive gas chromatography-tandem mass spectrometric method

Several countries have exempted synthetic nicotine from existing regulatory frameworks, resulting in the widespread substitution of synthetic nicotine (SN) in almost all e-cigarette products available. However, it remains uncertain whether the purported synthetic nicotine is indeed genuine SN. There is a need to develop biological indicators and an analytical method that more clearly distinguishes between the two sources. Impurities in neat tobacco-derived nicotine (TDN) were characterized and identified through non-targeted and targeted analysis. Gas chromatography-tandem mass spectrometry (GC-MS/MS) conditions were optimized for detecting biological indicators in e-cigarette products. Nine tobacco-related alkaloids were identified and selected as biological indicators for TDN. A liquid-liquid extraction and GC-MS/MS quantitative method were developed to detect nine biological indicators in e-cigarette products with the limit of quantification ranging from 0.2 to 4.2 µg L-1 using 0.5 mL of e-liquid. This method was applied to 50 e-cigarette brands purchased in the Korean market. The developed method was able to easily and accurately identify the origin of nicotine even using a small amount of e-liquid sample. It is expected that effective e-cigarette regulation will be possible if the nicotine biological indicator and high-sensitivity analysis method developed in this study are used.

Advances in regulatory mechanism(s) and biotechnological approaches to modulate nicotine content in tobacco

More than 8 million deaths are caused by tobacco-related diseases every year. A staggering 1.2 million of those fatalities occur due to second-hand smoke exposure among non-smokers, but more than 7 million are due to direct tobacco use among smokers. Nicotine acts as the key ingredient triggering the addiction. The United States Food and Drug Administration (FDA) has classified more than 90 chemical components of tobacco and related smoke as hazardous or potentially hazardous leading to cancer, cardiovascular, respiratory, and reproductive disorders. Hence, reducing nicotine content has been the foremost objective to reduce health and death risks. Therefore, various biotechnological approaches for developing tobacco varieties with low nicotine concentrations are urgently required for the welfare of humankind. In recent years, numerous advancements have been made in nicotine-based tobacco research, suggesting regulatory components involved in nicotine biosynthesis and developing nicotine-less tobacco varieties through biotechnological approaches. This review highlights the various regulatory components and major approaches used to modulate nicotine content in tobacco cultivars.

Plant disease resistance outputs regulated by AP2/ERF transcription factor family

Plants have evolved a complex and elaborate signaling network to respond appropriately to the pathogen invasion by regulating expression of defensive genes through certain transcription factors. The APETALA2/ethylene response factor (AP2/ERF) family members have been determined as key regulators in growth, development, and stress responses in plants. Moreover, a growing body of evidence has demonstrated the critical roles of AP2/ERFs in plant disease resistance. In this review, we describe recent advances for the function of AP2/ERFs in defense responses against microbial pathogens. We summarize that AP2/ERFs are involved in plant disease resistance by acting downstream of mitogen activated protein kinase (MAPK) cascades, and regulating expression of genes associated with hormonal signaling pathways, biosynthesis of secondary metabolites, and formation of physical barriers in an MAPK-dependent or -independent manner. The present review provides a multidimensional perspective on the functions of AP2/ERFs in plant disease resistance, which will facilitate the understanding and future investigation on the roles of AP2/ERFs in plant immunity.

From cultivation to cancer: formation of N-nitrosamines and other carcinogens in smokeless tobacco and their mutagenic implications

Tobacco use is a major cause of preventable morbidity and mortality globally. Tobacco products, including smokeless tobacco (ST), generally contain tobacco-specific N-nitrosamines (TSNAs), such as N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-butanone (NNK), which are potent carcinogens that cause mutations in critical genes in human DNA. This review covers the series of biochemical and chemical transformations, related to TSNAs, leading from tobacco cultivation to cancer initiation. A key aim of this review is to provide a greater understanding of TSNAs: their precursors, the microbial and chemical mechanisms that contribute to their formation in ST, their mutagenicity leading to cancer due to ST use, and potential means of lowering TSNA levels in tobacco products. TSNAs are not present in harvested tobacco but can form due to nitrosating agents reacting with tobacco alkaloids present in tobacco during certain types of curing. TSNAs can also form during or following ST production when certain microorganisms perform nitrate metabolism, with dissimilatory nitrate reductases converting nitrate to nitrite that is then released into tobacco and reacts chemically with tobacco alkaloids. When ST usage occurs, TSNAs are absorbed and metabolized to reactive compounds that form DNA adducts leading to mutations in critical target genes, including the RAS oncogenes and the p53 tumor suppressor gene. DNA repair mechanisms remove most adducts induced by carcinogens, thus preventing many but not all mutations. Lastly, because TSNAs and other agents cause cancer, previously documented strategies for lowering their levels in ST products are discussed, including using tobacco with lower nornicotine levels, pasteurization and other means of eliminating microorganisms, omitting fermentation and fire-curing, refrigerating ST products, and including nitrite scavenging chemicals as ST ingredients.

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.

Current Status and De Novo Synthesis of Anti-Tumor Alkaloids in Nicotiana

Alkaloids are the most diversified nitrogen-containing secondary metabolites, having antioxidant and antimicrobial properties, and are extensively used in pharmaceuticals to treat different types of cancer. Nicotiana serves as a reservoir of anti-cancer alkaloids and is also used as a model plant for the de novo synthesis of various anti-cancer molecules through genetic engineering. Up to 4% of the total dry weight of Nicotiana was found to be composed of alkaloids, where nicotine, nornicotine, anatabine, and anabasine are reported as the dominant alkaloids. Additionally, among the alkaloids present in Nicotiana, β-carboline (Harmane and Norharmane) and Kynurenines are found to show anti-tumor effects, especially in the cases of colon and breast cancers. Creating new or shunting of existing biosynthesis pathways in different species of Nicotiana resulted in de novo or increased synthesis of different anti-tumor molecules or their derivatives or precursors including Taxadiane (~22.5 µg/g), Artemisinin (~120 μg/g), Parthenolide (~2.05 ng/g), Costunolide (~60 ng/g), Etoposide (~1 mg/g), Crocin (~400 µg/g), Catharanthine (~60 ng/g), Tabersonine (~10 ng/g), Strictosidine (~0.23 mg/g), etc. Enriching the precursor pool, especially Dimethylallyl Diphosphate (DMAPP), down-regulating other bi-product pathways, compartmentalization or metabolic shunting, or organelle-specific reconstitution of the precursor pool, might trigger the enhanced accumulation of the targeted anti-cancer alkaloid in Nicotiana.

Systematic Identification of Methyl Jasmonate-Responsive Long Noncoding RNAs and Their Nearby Coding Genes Unveils Their Potential Defence Roles in Tobacco BY-2 Cells

Long noncoding RNAs (lncRNAs) are distributed in various species and play critical roles in plant growth, development, and defence against stimuli. However, the lncRNA response to methyl jasmonate (MeJA) treatment has not been well characterized in Nicotiana tabacum Bright Yellow-2 (BY-2) cells, and their roles in plant defence remain elusive. Here, 7848 reliably expressed lncRNAs were identified in BY-2 cells, of which 629 differentially expressed (DE) lncRNAs were characterized as MeJA-responsive lncRNAs. The lncRNAs in BY-2 cells had a strong genus specificity in Nicotiana. The combined analysis of the cis-regulated lncRNAs and their target genes revealed the potential up- and downregulated target genes that are responsible for different biological functions and metabolic patterns. In addition, some lncRNAs for response-associated target genes might be involved in plant defence and stress resistance via their MeJA- and defence-related cis-regulatory elements. Moreover, some MeJA-responsive lncRNA target genes were related to quinolinate phosphoribosyltransferase, lipoxygenases, and endopeptidase inhibitors, which may contribute to nicotine synthesis and disease and insect resistance, indicating that MeJA-responsive lncRNAs regulate nicotine biosynthesis and disease resistance by regulating their potential target genes in BY-2 cells. Therefore, our results provide more targets for genetically engineering the nicotine content and plant defence in tobacco plants.

Interplay of transcription factors orchestrating the biosynthesis of plant alkaloids

Plants produce a range of secondary metabolites primarily as defence molecules. A plant has to invest considerable energy to synthesise alkaloids, and sometimes they are even toxic to themselves. Hence, the biosynthesis of alkaloids is a spatiotemporally regulated process under quantitative feedback regulation which is accomplished by the signal reception, transcriptional/translational regulation, transport, storage and accumulation. The transcription factors (TFs) initiate the biosynthesis of alkaloids after appropriate cues. The present study recapitulates last decade understanding of the role of TFs in alkaloid biosynthesis. The present review discusses TF families, viz. AP2/ERF, bHLH, WRKY, MYB involved in the biosynthesis of various types of alkaloids. It also highlights the role of the jasmonic acid cascade and post-translational modifications of TF proteins. A thorough understanding of TFs will help us to decide a strategy to facilitate successful pathway manipulation and in vitro production.

Evaluation of biotransformation capacity of transplastomic plants and hairy roots of Nicotiana tabacum expressing human cytochrome P450 2D6

Cytochrome P450 monooxygenases (CYPs) are important tools for regio- and stereoselective oxidation of target molecules or engineering of metabolic pathways. Functional heterologous expression of eukaryotic CYPs is often problematic due to their dependency on the specific redox partner and the necessity of correct association with the membranes for displaying enzymatic activity. Plant hosts offer advantages of accessibility of reducing partners and a choice of membranes to insert heterologous CYPs. For the evaluation of plant systems for efficient CYP expression, we established transplastomic plants and hairy root cultures of Nicotiana tabacum carrying the gene encoding human CYP2D6 with broad substrate specificity. The levels of CYP2D6 transcript accumulation and enzymatic activity were estimated and compared with the data of CYP2D6 transient expression in N. benthamiana. The relative level of CYP2D6 transcripts in transplastomic plants was 2-3 orders of magnitude higher of that observed after constitutive or transient expression from the nucleus. CYP2D6 expressed in chloroplasts converted exogenous synthetic substrate loratadine without the need for co-expression of the cognate CYP reductase. The loratadine conversion rate in transplastomic plants was comparable to that in N. benthamiana plants transiently expressing a chloroplast targeted CYP2D6 from the nucleus, but was lower than the value reported for transiently expressed CYP2D6 with the native endoplasmic reticulum signal-anchor sequence. Hairy roots showed the lowest substrate conversion rate, but demonstrated the ability to release the product into the culture medium. The obtained results illustrate the potential of plant-based expression systems for exploiting the enzymatic activities of eukaryotic CYPs with broad substrate specificities.

CLCNt2 Mediates Nitrate Content in Tobacco Leaf, Impacting the Production of Tobacco-Specific Nitrosamines in Cured Leaves

Nitrate accumulation in tobacco (Nicotiana tabacum L.) leaf, particularly in the burley (BU) type, is a reservoir for the generation of nitrosating agents responsible for the formation of tobacco-specific nitrosamines (TSNAs). TSNAs are mainly produced via the nitrosation of alkaloids occurring during the curing of tobacco leaves. Additional formation of TSNAs may also occur during tobacco storage, leaf processing and in some circumstances via pyrosynthesis during combustion. Two TSNA species, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N-nitrosonornicotine (NNN) are found in the tobacco products and have been documented to be animal carcinogens. A previous study showed that decreasing the accumulation of nitrate in tobacco leaf via the overexpression of a deregulated form of nitrate reductase is efficient to reduce the production of TSNAs. We pursue in finding another molecular genetic target to lower nitrate in BU tobacco. Suppressing expression or knocking-out CLCNt2 has a direct impact on leaf nitrate and TSNA reduction in cured leaves without altering biomass. This study provides now a straight path toward the development of new commercial tobacco varieties with reduced TSNA levels by breeding of variants deficient in active CLCNt2 copies.

Natural history-guided omics reveals plant defensive chemistry against leafhopper pests

Although much is known about plant traits that function in nonhost resistance against pathogens, little is known about nonhost resistance against herbivores, despite its agricultural importance. Empoasca leafhoppers, serious agricultural pests, identify host plants by eavesdropping on unknown outputs of jasmonate (JA)-mediated signaling. Forward- and reverse-genetics lines of a native tobacco plant were screened in native habitats with native herbivores using high-throughput genomic, transcriptomic, and metabolomic tools to reveal an Empoasca-elicited JA-JAZi module. This module induces an uncharacterized caffeoylputrescine-green leaf volatile compound, catalyzed by a polyphenol oxidase in a Michael addition reaction, which we reconstitute in vitro; engineer in crop plants, where it requires a berberine bridge enzyme-like 2 (BBL2) for its synthesis; and show that it confers resistance to leafhoppers. Natural history-guided forward genetics reveals a conserved nonhost resistance mechanism useful for crop protection.

NtMYB305a binds to the jasmonate-responsive GAG region of NtPMT1a promoter to regulate nicotine biosynthesis

MYB transcription factors play essential roles in regulating plant secondary metabolism and jasmonate (JA) signaling. Putrescine N-methyltransferase is a key JA-regulated step in the biosynthesis of nicotine, an alkaloidal compound highly accumulated in Nicotiana spp. Here we report the identification of NtMYB305a in tobacco (Nicotiana tabacum) as a regulatory component of nicotine biosynthesis and demonstrate that it binds to the JA-responsive GAG region, which comprises a G-box, an AT-rich motif, and a GCC-box-like element, in the NtPMT1a promoter. Yeast one-hybrid analysis, electrophoretic mobility shift assay and chromatin immunoprecipitation assays showed that NtMYB305a binds to the GAG region in vitro and in vivo. Binding specifically occurs at the ∼30-bp AT-rich motif in a G/C-base-independent manner, thus defining the AT-rich motif as previously unknown MYB-binding element. NtMYB305a localized in the nucleus of tobacco cells where it is capable of activating the expression of a 4×GAG-driven GUS reporter in an AT-rich motif-dependent manner. NtMYB305a positively regulates nicotine biosynthesis and the expression of NtPMT and other nicotine pathway genes. NtMYB305a acts synergistically with NtMYC2a to regulate nicotine biosynthesis, but no interaction between these two proteins was detected. This identification of NtMYB305a provides insights into the regulation of nicotine biosynthesis and extends the roles played by MYB transcription factors in plant secondary metabolism.

A spatial-temporal understanding of gene regulatory networks and NtARF-mediated regulation of potassium accumulation in tobacco

MAIN CONCLUSION

After tobacco topping, changes in the auxin content could affect K+ uptake by inhibiting the activity of K+ uptake-related genes through the NtARF genes, thus causing changes in K+ content. Tobacco (Nicotiana tabacum) is a valuable industrial and commercial crop, and the leaf is its primary product. Topping (removing apical buds) is a common agronomic practice that significantly improves the yield of tobacco leaves. Potassium (K+) plays an important physiological role in tobacco growth and leaf traits, including combustibility, aroma, and safety in cigarette products, and its levels are significantly decreased after topping. Here, to present global spatial-temporal gene expression profiles and gene regulatory networks of the core elements of K+ uptake, leaves and roots from topped and untopped plants at short- and long-term time points after topping were sampled for transcriptome analysis. We found that the wounding response was initiated in leaves in the early stages after topping. Then, in the long term, processes related to metabolism and transcription regulation, as well as ion binding and transport, were altered. The expression profiles showed that core elements of K+ uptake and xylem loading were drastically suppressed in roots after topping. Finally, transient expression experiments confirmed that changes in the auxin content could affect K+ uptake by inhibiting the activity of K+ uptake-related genes through the tobacco auxin response factor (NtARF) genes, thus causing changes in the K+ content. These results suggest that some ARFs could be selected as targets to enhance the expressions of K+ uptake transporters, leading to increment of K+ contents and improvement of leaf quality in tobacco breeding.

Metabolic changes in leaves of N. tabacum and N. benthamiana during plant development

Dwindling fossil fuel reserves and poor environmental credentials of chemical synthesis means, new renewable sources for the production and manufacture of valuable chemicals and pharmaceuticals are required. Presently, tobacco is an underutilised non-food crop with the potential to act as a biofactory. In this study, metabolite profiling across vegetative development has been carried out to provide a quantitative baseline of metabolites, their formation and interaction. Two tobacco platforms have been used, Nicotiana benthamiana and Nicotiana tabacum. Our data generated has provided the quantitative and qualitative baseline levels for exploitable pathways and metabolites, across two complementary Nicotiana species. N. benthamiana is the chassis of choice for transient expression. The metabolite data obtained for N. benthamiana highlighted that before flower emergence, the increased central carbon metabolism and high amino acid levels are available for the biosynthesis of endogenous or heterologous metabolites. In the future, engineering pathways or biocatalysts into N. benthamiana could add value to the process presently used to produce low volume, high cost pharmaceuticals. Similar outputs were obtained for N. tabacum, which has the advantage of providing a large biomass and hence, high product yield. These data provide an insight into the metabolite pools available in tobacco for future exploitation by emerging New Plant Breeding Techniques.

Cytochrome P450 Enzymes as Key Drivers of Alkaloid Chemical Diversification in Plants

Plants produce more than 20,000 nitrogen-containing heterocyclic metabolites called alkaloids. These chemicals serve numerous eco-physiological functions in the plants as well as medicines and psychedelic drugs for human for thousands of years, with the anti-cancer agent vinblastine and the painkiller morphine as the best-known examples. Cytochrome P450 monooxygenases (P450s) play a key role in generating the structural variety that underlies this functional diversity of alkaloids. Most alkaloid molecules are heavily oxygenated thanks to P450 enzymes' activities. Moreover, the formation and re-arrangement of alkaloid scaffolds such as ring formation, expansion, and breakage that contribute to their structural diversity and bioactivity are mainly catalyzed by P450s. The fast-expanding genomics and transcriptomics databases of plants have accelerated the investigation of alkaloid metabolism and many players behind the complexity and uniqueness of alkaloid biosynthetic pathways. Here we discuss recent discoveries of P450s involved in the chemical diversification of alkaloids and how these inform our approaches in understanding plant evolution and producing plant-derived drugs.

The scaffold-forming steps of plant alkaloid biosynthesis

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