Quinolizidine Alkaloids and Isoflavones from the Herb of Thermopsis lupinoides and Their Antiviral, Antifungal, and Insecticidal Activities

As part of our ongoing investigation of natural bioactive substances from the genus Thermopsis of the tribe Fabaceae for agricultural protection, the chemical constituents of the herb Thermopsis lupinoides were systematically investigated, which led to the isolation of 39 quinolizidine alkaloids (QAs) (1-39), including 14 new QAs (1-14) and 14 isoflavones (40-53). Their structures were elucidated through comprehensive spectroscopic data analysis (IR, UV, NMR, HRESIMS), ECD calculations, and X-ray crystallography. The antitomato spotted wilt virus (TSWV) and antifungal (against Botrytis cinerea, Gibberella zeae, Phytophythora capsica, and Alternaria alternata) and insecticidal (against Aphis fabae and Tetranychus urticae) activities of the isolated compounds were screened using the lesion counting method, mycelial inhibition assay, and spray method, respectively. The bioassay results showed that 34 exhibited excellent protective activity against TSWV, with an EC50 value of 36.04 μg/mL, which was better than that of the positive control, ningnanmycin (86.03 μg/mL). The preliminary mechanistic exploration illustrated that 34 induced systemic acquired resistance in the host plant by acting on the salicylic acid signaling pathway. Moreover, 1 showed significant antifungal activity against B. cinerea (EC50 value of 20.83 μg/mL), while 2 exhibited good insecticidal activity against A. fabae (LC50 value of 24.97 μg/mL). This research is promising for the invention of novel pesticides from QAs with high efficiency and satisfactory ecological compatibility.

Three new quinolizidine alkaloids from the roots of Sophora tonkinensis

Three new quinolizidine alkaloids (1 - 3), including one new naturally isoflavone and cytisine polymer (3), along with 6 known ones were isolated from the ethanol extract of Sophora tonkinensis Gagnep. Their structures were elucidated by comprehensive spectroscopic data analysis (IR, UV, HRESIMS, 1D and 2D NMR), combined with ECD calculations. The antifungal activity against Phytophythora capsica, Botrytis cinerea, Gibberella zeae, and Alternaria alternata of the compounds was evaluated in a mycelial inhibition assay. Biological tests indicated that compound 3 exhibited strong antifungal activity against P. capsica with EC50 values of 17.7 μg/ml.

Community ecological succession of endophytic fungi associates with medicinal compound accumulation in Sophora alopecuroides

Endophytic fungi of medicinal plants are symbiotic with the host and play an important role in determining metabolites. To understand the relationship between the accumulation of Sophora alopecuroides' medicinal bioactive compounds and the ecological succession of endophytic fungi, here we collected samples from S. alopecuroides at four developmental stages (adult, flowering, podding, and mature) and different organs (roots, stems, leaves, and seeds) at the mature stage. We then used high-performance liquid chromatography-mass spectrometry and high-throughput sequencing on the internal transcribed spacer region to identify the medicinal compounds and endophytic fungal communities in each sample. The endophytic fungal community characteristics and accumulation of medicinally bioactive compounds of S. alopecuroides varied with the host's developmental stages and organs, with the highest total alkaloids content of 111.9 mg/g at the mature stage. Membership analysis and network connection analysis showed a total of 15 core endophytic fungi in different developmental stages and 16 core endophytic fungi in different organs at the mature stage. The unclassified Ascomycota, Aspergillus, and Alternaria were significantly and positively correlated with the medicinal compounds of S. alopecuroides at the mature stage (r > 0.6 or r < -0.6; P < 0.05). In this study, we identified key endophytic fungal resources that affect the content of medicinally bioactive compounds in S. alopecuroides. This discovery could lay the foundation for enhancing the yield of medicinally bioactive compounds in S. alopecuroides and the development and application of functional endophytic fungi.IMPORTANCESophora alopecuroides is a traditional Chinese herbal medicine. The major medicinal chemicals are considered to be quinolizidine alkaloids. Quinolizidine alkaloids have been widely used for the treatment of tumors, dysentery, and enteritis. Previous studies have found that endophytic fungi in S. alopecuroides can promote the accumulation of host quinolizidine alkaloids. However, the relationship between the accumulation of S. alopecuroides' medicinal bioactive compounds and the ecological succession of endophytic fungi remains unclear. In this study, we screened the key endophytic fungal resources affecting the content of medicinally bioactive compounds and laid the foundation for subsequent research on the mechanism by which endophytic fungi promote the accumulation of medicinally bioactive compounds in S. alopecuroides.

Quantitation of Lupinus spp. Quinolizidine Alkaloids by qNMR and Accelerated Debittering with a Resin-Based Protocol

Quinolizidine alkaloids (QAs) are toxic secondary metabolites of the Lupinus species, the presence of which limits the expansion of lupin beans consumption, despite their high protein content. Evaluation of the level of alkaloids in edible Lupinus species is crucial from a food safety point of view. However, quantitation of QAs is complicated by the fact that not all important alkaloids used for quantitation are commercially available. In this context, we developed a method for the simultaneous quantitation of eight major lupin alkaloids using quantitative NMR spectroscopy (qNMR). Quantitation and analysis were performed in 15 different seed extracts of 11 Lupinus spp. some of which belonged to the same species, with different geographical origins and time of harvest, as well as in all aerial parts of L. pilosus. The mature seeds of L. pilosus were found to be a uniquely rich source of multiflorine. Additionally, we developed a protocol using adsorption or ionic resins for easy, fast, and efficient debittering of the lupine seeds. The protocol was applied to L. albus, leading to a decrease of the time required for alkaloids removal as well as water consumption and to a method for QA isolation from the debittering wastewater.

Impacts of Different Processes on the Nutritional and Antinutritional Contents of White and Blue Lupin Seeds and Usage Possibilities for Sustainable Poultry Production

In the current era, it is important to consider economic and ecological sustainability issues while optimally meeting the nutrient needs of poultry. The use and research of alternative feedstuffs have gained importance due to these factors. The aim of this study is to reveal the raw lupin seeds' nutrient ingredients as an alternative feedstuff and the effects of debittering methods. In the present study, two different treatments (germination for 2 days; heat treatment in an autoclave at 130 °C for 20 min) were applied to white and blue lupin seeds, and the differences in nutrient compositions between them and raw seeds were determined. When fatty acid compositions were analyzed, oleic, γ-linolenic, arachidic, behenic, erucic, and lignoceric acid values were found to be the highest in the raw, autoclaved, and germinated forms of white lupin (p < 0.01). The highest values of palmitic, stearic, and linoleic acids were observed in blue lupin (p < 0.01). While the value of total quinolizidine alkaloids (QA) in raw white lupin grains was higher than 1.943 mg/g, it was higher than 1.800 mg/g in autoclaved and germination-treated grains. Similarly, the total QA value of raw blue lupin grains was 0.894 mg/g, 0.609 ± 0.244 mg/g in germination-treated seeds, and 0.705 ± 0.282 mg/g in autoclave-treated seeds. As a result of these findings, it can be said that the methods applied for the removal of bitterness gave promising results. Furthermore, it would be rewarding to use these lupin varieties in in vitro and in vivo experiments to reveal the impacts and mechanisms of debittering methods on poultry.

Phytotoxic activity of Ulex europaeus, an invasive plant on Chilean ecosystems: separation and identification of potential allelochemicals

Despite its worldwide relevance as an invasive plant, there are few studies on Ulex europaeus (gorse) and its allelopathic activity is almost unexplored. The allelochemical profile of gorse was analysed through methanolic extract of pods and roots, and its phytotoxic effects on Lactuca sativa germination. The methanolic extract of pods had no effect in germination, while extract of roots resulted in a U-shaped dose-response curve: reducing the germination at concentration 0.5 mg mL^-1. GC-MS analysis detected compounds with proven antimicrobial and antioxidant activities in the pods and cytotoxic compounds in the roots, which could explain the bioassay results. The quinolizidine alkaloids (QAs) composition was evaluated to predict possible biological functions. It showed the presence of QAs in gorse that are absent in their native range, indicating broad defense strategies against bacteria, fungi, plants, and insects in the Chilean ecosystem. This could explain the superiority of gorse in the invaded areas.

Combined Gamma Conglutin and Lupanine Treatment Exhibits In Vivo an Enhanced Antidiabetic Effect by Modulating the Liver Gene Expression Profile

Previous studies have individually shown the antidiabetic potential of gamma conglutin (Cγ) and lupanine from lupins. Until now, the influence of combining both compounds and the effective dose of the combination have not been assessed. Moreover, the resulting gene expression profile from this novel combination remains to be explored. Therefore, we aimed to evaluate different dose combinations of Cγ and lupanine by the oral glucose tolerance test (OGTT) to identify the higher antidiabetic effect on a T2D rat model. Later, we administered the selected dose combination during a week. Lastly, we evaluated biochemical parameters and liver gene expression profile using DNA microarrays and bioinformatic analysis. We found that the combination of 28 mg/kg BW Cγ + 20 mg/kg BW lupanine significantly reduced glycemia and lipid levels. Moreover, this treatment positively influenced the expression of Pdk4, G6pc, Foxo1, Foxo3, Ppargc1a, Serpine1, Myc, Slc37a4, Irs2, and Igfbp1 genes. The biological processes associated with these genes are oxidative stress, apoptosis regulation, and glucose and fatty-acid homeostasis. For the first time, we report the beneficial in vivo effect of the combination of two functional lupin compounds. Nevertheless, further studies are needed to investigate the pharmacokinetics and pharmacodynamics of the Cγ + lupanine combined treatment.

A pan-genome and chromosome-length reference genome of narrow-leafed lupin (Lupinus angustifolius) reveals genomic diversity and insights into key industry and biological traits

Narrow-leafed lupin (NLL; Lupinus angustifolius) is a key rotational crop for sustainable farming systems, whose grain is high in protein content. It is a gluten-free, non-genetically modified, alternative protein source to soybean (Glycine max) and as such has gained interest as a human food ingredient. Here, we present a chromosome-length reference genome for the species and a pan-genome assembly comprising 55 NLL lines, including Australian and European cultivars, breeding lines and wild accessions. We present the core and variable genes for the species and report on the absence of essential mycorrhizal associated genes. The genome and pan-genomes of NLL and its close relative white lupin (Lupinus albus) are compared. Furthermore, we provide additional evidence supporting LaRAP2-7 as the key alkaloid regulatory gene for NLL and demonstrate the NLL genome is underrepresented in classical NLR disease resistance genes compared to other sequenced legume species. The NLL genomic resources generated here coupled with previously generated RNA sequencing datasets provide new opportunities to fast-track lupin crop improvement.

Correlation in endophytic fungi community diversity and bioactive compounds of Sophora alopecuroides

Sophora alopecuroides L. is a traditional Chinese medicine used for the treatment of several different disease states including bacillary dysentery and enteritis. But importantly, it also plays a role as an anti-tumor agent. That said, little is known about the role endophytes play regarding the clinically bioactive metabolites in S. alopecuroides. In order to explore the effects of endophytic fungi on the accumulation, quality, and correlation in the content of the medicinal compounds, the structural diversity of endophytic fungi in S. alopecuroides was analyzed. The relationship between endophytes and quinolizidine alkaloids (QAs), housed within the seeds of S. alopecuroides, which were interpreted based on established methods of high-throughput sequencing and high-performance liquid chromatography. A total of 1,034,418 effective sequence reads and 257 operational taxonomic units (OTUs) were obtained from 33 samples which were sourced from 11 different sampling sites and further classified into 9 phyla, 20 classes, 45 orders, 85 families, and 118 genera. Ascomycota was found to be the dominant phylum of endophytic fungi in S. alopecuroides, with a relative abundance ranging from 60.85 to 98.30%. Alternaria, Cladosporium, Filobasidium, and an unidentified Ascomycota were the core-shared endophytes, accounting for 49.96, 27.12, 14.83, and 7.88%, respectively. Correlation analysis showed that the Simpson's diversity index of endophytic fungal community in S. alopecuroides was significantly positively correlated with the Oxymatrine (OMA) content in different areas, while the Chao and Shannoneven indexes were significantly negatively correlated with OMA. The endophytic fungi of Alternaria were positively correlated with the content of OMA, Oxysophocarpine (OSC), and total QAs. This study has mastered the endophytic fungi resources of S. alopecuroides, explored potential functional endophytic fungi, and provided a scientific basis for using biological fertilization strategies to improve the quality of S. alopecuroides.

Quinolizidine Alkaloids with Antitomato Spotted Wilt Virus and Insecticidal Activities from the Seeds of Thermopsis lanceolata R. Br

As part of our ongoing investigation of pesticide active quinolizidine alkaloids (QAs) from the family Fabaceae, the chemical constituents of the seeds of Thermopsis lanceolata R. Br. were systematically investigated. Bioassay-guided fractionation and purification of the crude extract led to the isolation of seventeen new QAs (1-17), including three new naturally occurring compounds (15-17), along with 15 known compounds (18-32). Their structures were elucidated by comprehensive spectroscopic data analysis (IR, UV, NMR, and HRESIMS) and quantum chemistry calculations (¹³C NMR and ECD). The antitomato spotted wilt virus activities and insecticidal activities against Aphis fabae, Nilaparvata lugens (Stal), and Tetranychus urticae of compounds 1-32 were screened using the lesion counting method, spray method, and rice-stem dipping method, respectively. Biological tests indicated that compounds 6, 9, 10, and 18 displayed significant anti-TSWV activities compared with the positive control ningnanmycin. Compounds 3, 4, and 5 showed better insecticidal activities against A. fabae with LC₅₀ values of 10.07, 12.07, and 6.56 mg/L, respectively. Moreover, compounds 5, 18, and 24 exhibited moderate insecticidal activities against N. lugens (Stal) with LC₅₀ values of 37.91, 53.44, and 31.21 mg/L, respectively. Furthermore, compounds 9 and 10 exhibited moderate insecticidal activities against T. urticae.

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

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

New quinolizidine alkaloid and insecticidal activity of Sophora secundiflora and Sophora tomentosa against Culex pipiens (Diptera: Culicidae)

Phytochemical investigation of Sophora secundiflora alkaloid fraction led to isolation of one new quinolizidine alkaloid (1) 13-methoxyanagyrine together with six known ones (2-7). The insecticidal activity of 70% methanol extract of leaves of S. secundiflora, S. tomentosa and the isolated alkaloids were assessed against 3^rd instar larvae of Culex pipiens (Diptera: Culicidae) using different concentrations and mortality rate was recorded. Sophora tomentosa extract showed highest mortality rate with median lethal concentration LC₅₀ 3.11 ppm after 24 h and 0.66 ppm after 48 h and anagyrine (6) exhibited remarkably insecticidal activity with LC₅₀ value of 3.42 ppm after 24 h of exposure. Additionally, cytotoxic activity of alkaloid fraction of S. secundiflora, S. tomentosa and isolated alkaloids was also studied using crystal violet assay against MCF-7 and HEPG-2 cell lines. Anagyrine (6) exhibited IC₅₀ values of 27.3 ± 0.7 and 30.2 ± 0.9 µg/mL against MCF-7 and HEPG-2 cancer cells, respectively.

Thionation of quinolizidine alkaloids and their derivatives via Lawesson's reagent

Direct thionation of quinolizidine alkaloids (-)-cytisine, methylcytisine, thermopsine and some of their carbonyl derivatives was realized. It was established that carrying out of the reaction in the boiling toluene with 0.5 eq. of Lawesson's reagent (LR) is most effective for synthesis of thio analogues of methyl-, allyl-, benzylcytisine and thermopsine. It was found, that formation of thioamides is preferable in the case with starting 3-carboxamides of (-)-cytisine or 2-oxo and 4-oxo derivatives of methylcytisine; and an excess of LR is needed for their exhaustive thionation. It was shown, that thionation of 'cytisine substituted' urea and thiourea, as well as Diels-Alder adducts of methylcitisine with phenylmaleimide on basis of this approach was not quite successful: only thionation of the 2-pyridone core has occurred. It should be noted that transformation of urea and thiourea is complicated by side reactions leading to low yields of thio products, and the result of LR interaction with mentioned above diastereomeric Diels-Alder adducts depends on their stereochemistry and thermodynamic stability under reaction conditions.

Analysis of Genetic Diversity in the Traditional Chinese Medicine Plant 'Kushen' (Sophora flavescens Ait.)

Kushen root, from the woody legume Sophora flavescens, is a traditional Chinese medicine that is a key ingredient in several promising cancer treatments. This activity is attributed in part to two quinolizidine alkaloids (QAs), oxymatrine and matrine, that have a variety of therapeutic activities in vitro. Genetic selection is needed to adapt S. flavescens for cultivation and to improve productivity and product quality. Genetic diversity of S. flavescens was investigated using genotyping-by-sequencing (GBS) on 85 plants grown from seeds collected from 9 provinces of China. DArTSeq provided over 10,000 single nucleotide polymorphism (SNP) markers, 1636 of which were used in phylogenetic analysis to reveal clear regional differences for S. flavescens. One accession from each region was selected for PCR-sequencing to identify gene-specific SNPs in the first two QA pathway genes, lysine decarboxylase (LDC) and copper amine oxidase (CAO). To obtain SfCAO sequence for primer design we used a targeted transcript capture and assembly strategy using publicly available RNA sequencing data. Partial gene sequence analysis of SfCAO revealed two recently duplicated genes, SfCAO1 and SfCAO2, in contrast to the single gene found in the QA-producing legume Lupinus angustifolius. We demonstrate high efficiency converting SNPs to Kompetitive Allele Specific PCR (KASP) markers developing 27 new KASP markers, 17 from DArTSeq data, 7 for SfLDC, and 3 for SfCAO1. To complement this genetic diversity analysis a field trial site has been established in South Australia, providing access to diverse S. flavescens material for morphological, transcriptomic, and QA metabolite analysis. Analysis of dissected flower buds revealed that anthesis occurs before buds fully open suggesting a potential for S. flavescens to be an inbreeding species, however this is not supported by the relatively high level of heterozygosity observed. Two plants from the field trial site were analysed by quantitative real-time PCR and levels of matrine and oxymatrine were assessed in a variety of tissues. We are now in a strong position to select diverse plants for crosses to accelerate the process of genetic selection needed to adapt kushen to cultivation and improve productivity and product quality.

Effects of two debittering processes on the alkaloid content and quality characteristics of lupin (Lupinus mutabilis Sweet)

BACKGROUND

The presence of quinolizidine alkaloids (QAs) in the species Lupinus mutabilis Sweet limits the expansion of its consumption and use, despite its high protein content. The objective of this research was therefore to determine the effect of two thermal treatments, aqueous (ATT) and saline (STT), on the QAs and total protein content, as well as on the texture (fracturability and hardness), visual perception attributes - hue (H*), luminosity (L*) and chromatism (C*) - and grain size in three lupin varieties (INIAP-450, INIAP-451, and Criollo). The water consumption required by each treatment was also measured.

RESULTS

The debittering process with ATT helped to concentrate the total nitrogen by 560 g kg^-1 and decreased the grain hardness to 2037 gf (grams of force) in the Criollo variety, while the chromatic parameters H* and C* increased in the three varieties. The STT treatment was more efficient than the ATT treatment in terms of the time required and the volume of water used to reduce the QAs to safe levels for consumption (2.5-3.5 g kg^-1 ). The size of the grain increased to four times its original size; the luminosity L* decreased during cooking to a value of 41.49 in the Criollo variety and then increased to 57.42 during grain washing.

CONCLUSIONS

The STT treatment is advisable for lupin debittering, although the extent of the effect was dependent on the variety. © 2020 Society of Chemical Industry.

Quinolizidine alkaloids are transported to seeds of bitter narrow-leafed lupin

Narrow-leafed lupin (NLL, Lupinus angustifolius) is a promising legume crop that produces seeds with very high protein content. However, NLL accumulates toxic quinolizidine alkaloids (QAs) in most of its tissues, including the seeds. To determine the level of in situ biosynthesis in the seeds, we compared the accumulation of QAs with the expression of the biosynthetic gene lysine decarboxylase (LDC) in developing seeds and pods of a bitter (high-QA) variety of NLL. While QAs accumulated steadily in seeds until the drying phase, LDC expression was comparatively very low throughout seed development. In contrast, both QA accumulation and LDC expression peaked early in pods and decreased subsequently, reaching background levels at the onset of drying. We complemented these studies with MS imaging, which revealed the distribution patterns of individual QAs in cross-sections of pods and seeds. Finally, we show that a paternal bitter genotype does not influence the QA levels of F1 seeds grown on a maternal, low-QA genotype. We conclude that the accumulation of QAs in seeds of bitter NLL is mostly, if not exclusively, transported from other tissues. These results open the possibility of using transport engineering to generate herbivore-resistant bitter NLL varieties that produce QA-free seeds.

Variation of spacer type and topology of phenyl moiety in 2-pyridone core of 4-oxo-3-N-methylcytisine; effect of synthesized compounds on rat's behavior in conditioned passive avoidance reflex (CPAR) test

Novel derivatives of 4-oxo-3-methylcytisine with phenyl moiety bonded to starting molecule through various spacers were obtained from the 9-amino, -halo, -formyl and 11-halo precursors by reductive alkylation of amines, generation of amide, as well as thio- and carboxamide functions, cross-coupling reactions, aldehyde condensation and reduction of unsaturated 'C-C' bonds. Ability of synthesized compounds to influence the learning and memory was preliminary assessed in conditioned passive avoidance reflex (CPAR) test in rats. It was shown, that derivatives with phenyl group at 11 carbon atom influence the learning and memory in CPAR test more effectively than other compounds. The hit-compound (3-methyl-11-(2-phenylvinyl)-3,5,6-trihydro-2H-1,5-methanopyrido[1,2-a][1,5]diazocine-4,8(1H)-dione) with the best values of 'latency' and 'time spent in the dark compartment' has been identified as a perspective scaffold for synthesis of novel derivatives of (-)-cytisine with potential neuropharmacological activity.

[Bioactive quinolizidine alkaloids from Sophora tonkinensis]

Twelve quinolizidine alkaloids were isolated from Sophora tonkinensis by means of silica gel, preparative MPLC, and preparative HPLC. On analysis of NMR spectroscopic data, their structures were established as 3-(4-hydroxyphenyl)-4-(3-methoxy-4-hydroxyphenyl)-3,4-dehydroquinolizidine(1), lanatine A(2), cermizines C(3), senepodines G(4), senepodines H(5), jussiaeiines A(6), jussiaeiines B(7),(+)-5α-hydroxyoxysophocarpine(8),(-)-12β-hydroxyoxysophocarpine(9),(-)-clathrotropine(10),(-)-cytisine(11), and (-)-N-methylcytisine(12), respectively. Compounds 1-7 were first isolated from Sophora L. plant. In the in vitro assays,the isolated compounds 1, 3, 6-10 exhibited potent activity against CVB3 with IC₅₀ of 6.40, 3.25, 4.66, 3.21, 0.12, 0.23 and 1.60, and with selective index values(SI=TC₅₀/IC₅₀)of 12.0, 5.6, 13.0, 15.1, 50.1, 26.2, and 23.6, respectively. Compounds 1, 3, and 7 exhibited activity against staphylococcus aureus(ATCC 29213)with MICvalues of 8.0, 3.5, 6.0 g•L⁻¹, respectively. Compounds 1, 3, 7, and 12 exhibited activity against staphylococcus aureus(ATCC 33591)with MIC values of 18.0, 7.5, 8.0, 12.0 g•L⁻¹, respectively. Compounds 2, 6, 7 exhibited activity against Escherichia coli(ATCC 25922) with MIC values of 1.0, 3.2, 0.8 g•L⁻¹.

Transcript profiling of a bitter variety of narrow-leafed lupin to discover alkaloid biosynthetic genes

Lupins (Lupinus spp.) are nitrogen-fixing legumes that accumulate toxic alkaloids in their protein-rich beans. These anti-nutritional compounds belong to the family of quinolizidine alkaloids (QAs), which are of interest to the pharmaceutical and chemical industries. To unleash the potential of lupins as protein crops and as sources of QAs, a thorough understanding of the QA pathway is needed. However, only the first enzyme in the pathway, lysine decarboxylase (LDC), is known. Here, we report the transcriptome of a high-QA variety of narrow-leafed lupin (L. angustifolius), obtained using eight different tissues and two different sequencing technologies. In addition, we present a list of 33 genes that are closely co-expressed with LDC and that represent strong candidates for involvement in lupin alkaloid biosynthesis. One of these genes encodes a copper amine oxidase able to convert the product of LDC, cadaverine, into 1-piperideine, as shown by heterologous expression and enzyme assays. Kinetic analysis revealed a low KM value for cadaverine, supporting a role as the second enzyme in the QA pathway. Our transcriptomic data set represents a crucial step towards the discovery of enzymes, transporters, and regulators involved in lupin alkaloid biosynthesis.

Quinolizidine Alkaloid Biosynthesis in Lupins and Prospects for Grain Quality Improvement

Quinolizidine alkaloids (QAs) are toxic secondary metabolites found within the genus Lupinus, some species of which are commercially important grain legume crops including Lupinus angustifolius (narrow-leafed lupin, NLL), L. luteus (yellow lupin), L. albus (white lupin), and L. mutabilis (pearl lupin), with NLL grain being the most largely produced of the four species in Australia and worldwide. While QAs offer the plants protection against insect pests, the accumulation of QAs in lupin grain complicates its use for food purposes as QA levels must remain below the industry threshold (0.02%), which is often exceeded. It is not well understood what factors cause grain QA levels to exceed this threshold. Much of the early work on QA biosynthesis began in the 1970-1980s, with many QA chemical structures well-characterized and lupin cell cultures and enzyme assays employed to identify some biosynthetic enzymes and pathway intermediates. More recently, two genes associated with these enzymes have been characterized, however, the QA biosynthetic pathway remains only partially elucidated. Here, we review the research accomplished thus far concerning QAs in lupin and consider some possibilities for further elucidation and manipulation of the QA pathway in lupin crops, drawing on examples from model alkaloid species. One breeding strategy for lupin is to produce plants with high QAs in vegetative tissues while low in the grain in order to confer insect resistance to plants while keeping grain QA levels within industry regulations. With the knowledge achieved on alkaloid biosynthesis in other plant species in recent years, and the recent development of genomic and transcriptomic resources for NLL, there is considerable scope to facilitate advances in our knowledge of QAs, leading to the production of improved lupin crops.

Lupanine Improves Glucose Homeostasis by Influencing KATP Channels and Insulin Gene Expression

The glucose-lowering effects of lupin seeds involve the combined action of several components. The present study investigates the influence of one of the main quinolizidine alkaloids, lupanine, on pancreatic beta cells and in an animal model of type-2 diabetes mellitus. In vitro studies were performed with insulin-secreting INS-1E cells or islets of C57BL/6 mice. In the in vivo experiments, hyperglycemia was induced in rats by injecting streptozotocin (65 mg/kg body weight). In the presence of 15 mmol/L glucose, insulin secretion was significantly elevated by 0.5 mmol/L lupanine, whereas the alkaloid did not stimulate insulin release with lower glucose concentrations. In islets treated with l-arginine, the potentiating effect of lupanine already occurred at 8 mmol/L glucose. Lupanine increased the expression of the Ins-1 gene. The potentiating effect on secretion was correlated to membrane depolarization and an increase in the frequency of Ca²⁺ action potentials. Determination of the current through ATP-dependent K⁺ channels (K_ATP channels) revealed that lupanine directly inhibited the channel. The effect was dose-dependent but, even with a high lupanine concentration of 1 mmol/L or after a prolonged exposure time (12 h), the K_ATP channel block was incomplete. Oral administration of lupanine did not induce hypoglycemia. By contrast, lupanine improved glycemic control in response to an oral glucose tolerance test in streptozotocin-diabetic rats. In summary, lupanine acts as a positive modulator of insulin release obviously without a risk for hypoglycemic episodes.

Quinolizidine alkaloid biosynthesis: recent advances and future prospects

Lys-derived alkaloids, including piperidine, quinolizidine, indolizidine, and lycopodium alkaloids, are widely distributed throughout the plant kingdom. Several of these alkaloids have beneficial properties for humans and have been used in medicine. However, the molecular mechanisms underlying the biosynthesis of these alkaloids are not well understood. In the present article, we discuss recent advances in our understanding of Lys-derived alkaloids, especially the biochemistry, molecular biology, and biotechnology of quinolizidine alkaloid (QA) biosynthesis. We have also highlighted Lys decarboxylase (LDC), the enzyme that catalyzes the first committed step of QA biosynthesis and answers a longstanding question about the molecular entity of LDC activity in plants. Further prospects using current advanced technologies, such as next-generation sequencing, in medicinal plants have also been discussed.