Evolution of secondary metabolites in legumes (Fabaceae)

Legumes produce a high diversity of secondary metabolites which serve as defence compounds against herbivores and microbes, but also as signal compounds to attract pollinating and fruit-dispersing animals. As nitrogen-fixing organisms, legumes produce more nitrogen containing secondary metabolites than other plant families. Compounds with nitrogen include alkaloids and amines (quinolizidine, pyrrolizidine, indolizidine, piperidine, pyridine, pyrrolidine, simple indole, Erythrina, simple isoquinoline, and imidazole alkaloids; polyamines, phenylethylamine, tyramine, and tryptamine derivatives), non-protein amino acids (NPAA), cyanogenic glucosides, and peptides (lectins, trypsin inhibitors, antimicrobial peptides, cyclotides). Secondary metabolites without nitrogen are phenolics (phenylpropanoids, flavonoids, isoflavones, catechins, anthocyanins, tannins, lignans, coumarins and furanocoumarins), polyketides (anthraquinones), and terpenoids (especially triterpenoid, steroidal saponins, tetraterpenes). While some secondary metabolites have a wide distribution (flavonoids, triterpenes, pinitol), however, others occur in a limited number of taxa. The distributions of secondary metabolites with an irregular occurrence are mapped on a molecular phylogeny of the Fabaceae, reconstructed from a combined data set of nucleotide sequences from rbcL, matK and ITS genes. In most cases, the distribution patterns of secondary metabolites do not agree with the phylogeny of the plants producing them. In contrary, the distribution of many secondary metabolites is patchy and irregular. Thus, the use of phytochemical data to reconstruct a phylogeny of plants is often not informative and can be misleading. The patchy distribution may be due to convergent evolution, a contribution of endophytic fungi or more likely, to an early acquisition of the key genes of secondary metabolism in the evolution of land plants among others by horizontal gene transfer from bacteria. Thus it would be a matter of gene regulation whether these genes are active in some but not all taxa.     

Evolution of secondary metabolites from an ecological and molecular phylogenetic perspective

Secondary metabolites, at least the major ones present in a plant, apparently function as defence (against herbivores, microbes, viruses or competing plants) and signal compounds (to attract pollinating or seed dispersing animals). They are thus important for the plant's survival and reproductive fitness. Secondary metabolites therefore represent adaptive characters that have been subjected to natural selection during evolution. Molecular phylogenies of the Fabaceae, Solanaceae and Lamiaceae were reconstructed and employed as a framework to map and to interpret the distribution of some major defence compounds that are typical for the respective plant families; quinolizidine alkaloids and non-protein amino acids for legumes; tropane and steroidal alkaloids for Solanaceae, and iridoids and essential oils for labiates. The distribution of the respective compounds appears to be almost mutually exclusive in the families studied, implying a strong phylogenetic and ecological component. However, on a closer look, remarkable exceptions can be observed, in that certain metabolites are absent (or present) in a given taxon, although all the neighbouring and ancestral taxa express (or do not express, respectively) the particular trait. It is argued that these patterns might reflect differential expression of the corresponding genes that have evolved earlier in plant evolution. The inconsistent secondary metabolite profiles mean that the systematic value of chemical characters becomes a matter of interpretation in the same way as traditional morphological markers. Thus, the distribution of secondary metabolites has some value for taxonomy but their occurrence apparently reflects adaptations and particular life strategies embedded in a given phylogenetic framework.     

Review: Microbial synthesis of agrochemical metabolites

The synthesis of agrochemical metabolite reference standards by microbial cultures can serve as a useful alternative to conventional chemical synthesis, particularly when the chemical synthesis is difficult. Microbially generated metabolites of agrochemicals can also be useful for predicting degradative pathways in animals, plants and soils prior to conducting animal, plant and soil metabolism studies which are required by regulatory agencies to support agrochemical registrations. Examples from the literature are used to illustrate the utility of synthesizing metabolites of agrochemicals by common microbes. Received 17 January 1997/ Accepted in revised form 20 March 1997     

Enhancement of plant-microbe interactions using a rhizosphere metabolomics-driven approach and its application in the removal of polychlorinated biphenyls

Persistent organic pollutants, such as polychlorinated biphenyls (PCBs), are a global problem. We demonstrate enhanced depletion of PCBs using root-associated microbes, which can use plant secondary metabolites, such as phenylpropanoids. Using a "rhizosphere metabolomics" approach, we show that phenylpropanoids constitute 84% of the secondary metabolites exuded from Arabidopsis roots. Phenylpropanoid-utilizing microbes are more competitive and are able to grow at least 100-fold better than their auxotrophic mutants on roots of plants that are able to synthesize or overproduce phenylpropanoids, such as flavonoids. Better colonization of the phenylpropanoid-utilizing strain in a gnotobiotic system on the roots of flavonoid-producing plants leads to almost 90% removal of PCBs in a 28-d period. Our work complements previous approaches to engineer soil microbial populations based on opines produced by transgenic plants and used by microbes carrying opine metabolism genes. The current approach based on plant natural products can be applied to contaminated soils with pre-existing vegetation. This strategy is also likely to be applicable to improving the competitive abilities of biocontrol and biofertilization strains.     

Marine chemical ecology: what''s known and what''s next?

In this review, I summarize recent developments in marine chemical ecology and suggest additional studies that should be especially productive. Direct tests in both the field and laboratory show that secondary metabolites commonly function as defenses against consumers. However, some metabolites also diminish fouling, inhibit competitors or microbial pathogens, and serve as gamete attractants; these alternative functions are less thoroughly investigated. We know little about how consumers perceive secondary metabolites or how ecologically realistic doses of defensive metabolites affect consumer physiology or fitness, as opposed to feeding behavior. Secondary metabolites have direct consequences, but they do not act in isolation from other prey characteristics or from the physical and biological environment in which organisms interact with their natural enemies. This mandates that marine chemical ecology be better integrated into a broader and more complex framework that includes aspects of physiological, population, community, and even ecosystem ecology. Recent advances in this area involve assessing how chemically mediated interactions are affected by physical factors such as flow, desiccation, UV radiation, and nutrient availability, or by biological forces such as the palatability or defenses of neighbors, fouling organisms, or microbial symbionts. Chemical defenses can vary dramatically among geographic regions, habitats, individuals within a local habitat, and within different portions of the same individual. Factors affecting this variance are poorly known, but include physical stresses and induction due to previous attack. Studies are needed to assess which consumers induce prey defenses, how responses vary in environments with differing physical characteristics, and whether the ‘induced’ responses are a direct response to consumer attack or are a defense against microbial pathogens invading via feeding wounds. Although relatively unstudied, ontogenetic shifts in concentrations and types of defenses occur in marine species, and patterns of larval chemical defenses appear to provide insights into the evolution of complex life cycles and of differing modes of development among marine invertebrates. The chemical ecology of marine microbes is vastly underappreciated even though microbes produce metabolites that can have devastating indirect effects on non-target organisms (e.g., red tide related fish kills) and significantly affect entire ecosystems. The natural functions of these metabolites are poorly understood, but they appear to deter both consumers and other microbes. Additionally, marine macro-organisms use metabolites from microbial symbionts to deter consumers, subdue prey, and defend their embryos from pathogens. Microbial chemical ecology offers unlimited possibilities for investigators that develop rigorous and more ecologically relevant approaches.     

Microbial degradation of plant toxins

Plants produce a variety of secondary metabolites in response to biotic and abiotic stresses. Although they have many functions, a subclass of toxic secondary metabolites mainly serve plants as deterring agents against herbivores, insects, or pathogens. Microorganisms present in divergent ecological niches, such as soil, water, or insect and rumen gut systems have been found capable of detoxifying these metabolites. As a result of detoxification, microbes gain growth nutrients and benefit their herbivory host via detoxifying symbiosis. Here, we review current knowledge on microbial degradation of toxic alkaloids, glucosinolates, terpenes, and polyphenols with an emphasis on the genes and enzymes involved in breakdown pathways. We highlight that the insect-associated microbes might find application in biotechnology and become targets for an alternative microbial pest control strategy.     

培菌昆虫相关放线菌的次级代谢产物研究进展

昆虫共生微生物是一种特殊的微生物资源,其中放线菌在昆虫肠道、体表和巢穴中广泛分布。近年来,人们从培菌昆虫来源的放线菌中分离得到多种新型化合物,可以选择性抑制菌圃的致病真菌,部分还对植物致病真菌、昆虫致病真菌、人类病原菌和癌细胞有抑制活性。因此,研究培菌昆虫相关微生物不仅有助于了解宿主与微生物的共生机制,还能发掘新的活性物质,用于生物农药、生物医药的开发。本文对培菌昆虫来源放线菌次级代谢产物的研究进展进行了综述。     

Changing trends in biotechnology of secondary metabolism in medicinal and aromatic plants

Main conclusion

Medicinal and aromatic plants are known to produce secondary metabolites that find uses as flavoring agents, fragrances, insecticides, dyes and drugs. Biotechnology offers several choices through which secondary metabolism in medicinal plants can be altered in innovative ways, to overproduce phytochemicals of interest, to reduce the content of toxic compounds or even to produce novel chemicals. Detailed investigation of chromatin organization and microRNAs affecting biosynthesis of secondary metabolites as well as exploring cryptic biosynthetic clusters and synthetic biology options, may provide additional ways to harness this resource. Plant secondary metabolites are a fascinating class of phytochemicals exhibiting immense chemical diversity. Considerable enigma regarding their natural biological functions and the vast array of pharmacological activities, amongst other uses, make secondary metabolites interesting and important candidates for research. Here, we present an update on changing trends in the biotechnological approaches that are used to understand and exploit the secondary metabolism in medicinal and aromatic plants. Bioprocessing in the form of suspension culture, organ culture or transformed hairy roots has been successful in scaling up secondary metabolite production in many cases. Pathway elucidation and metabolic engineering have been useful to get enhanced yield of the metabolite of interest; or, for producing novel metabolites. Heterologous expression of putative plant secondary metabolite biosynthesis genes in a microbe is useful to validate their functions, and in some cases, also, to produce plant metabolites in microbes. Endophytes, the microbes that normally colonize plant tissues, may also produce the phytochemicals produced by the host plant. The review also provides perspectives on future research in the field.

     

Bottom‐up effects of glucosinolate variation on aphid colony dynamics in wild cabbage populations

1. There is an ongoing debate about the relative importance of top‐down and bottom‐up regulation of herbivore dynamics in the wild. Secondary metabolites, produced by plants, have negative effects on survival and growth of some herbivore species, causing bottom‐up regulation of population dynamics. Herbivore natural enemies may use plant secondary metabolites as cues to find their prey, but their survival and reproduction can also be influenced by the upward cascade of secondary metabolites through the food web. Thus plant chemistry might also affect herbivore populations by mediating top‐down regulation. 2. We investigated the influence of heritable variation in aliphatic glucosinolates, a class of secondary metabolites produced by Brassica plants, on the relative importance of top‐down and bottom‐up regulation of Brevicoryne brassicae (mealy cabbage aphid) colonies in natural Brassica oleracea (wild cabbage) populations. We manipulated natural enemy pressure on plants differing in their glucosinolate profiles, and monitored aphid colony growth and disperser production. 3. Aphid colony sizes were significantly smaller on plants producing sinigrin, compared with plants producing alternative aliphatic glucosinolates. Aphid natural enemy numbers correlated with aphid colony size, but there was no additional effect of the plants' chemical phenotype on natural enemy abundance. Furthermore, experimental reduction of natural enemy pressure had no effect on aphid colony size or production of winged dispersers. 4. Our results provide evidence for glucosinolate‐mediated, bottom‐up regulation of mealy cabbage aphid colonies in natural populations, but we found no indication of top‐down regulation. We emphasise that more studies of these processes should focus on tritrophic interactions in the wild.     

Die Wasserlinse – eine unterschätzte Vielzweckpflanze

Tiny, inconspicuous duckweeds (Lemnaceae) are often considered a nuisance, due to their propensity to rapidly cover surfaces of water bodies. However, their pronounced growth potential, together with their particular morphological, clonal and genomic properties and their easy cultivation make them valuable model plants for studies, and have established them as indicator plants in the field of ecotoxicology. Duckweeds can make a valuable contribution to wastewater remediation, and the biomass that their growth thereby provides can be of value in many ways, including energy generation, fuel production and use as fertilizer and animal food. Duckweeds grown under controlled conditions can contribute to human nutrition and serve as biofactories for heterologous protein expression. The versatile usage potential of duckweeds has not been thoroughly exploited, as it could and should be in the future.     

Secondary metabolism: regulation and role in fungal biology

Filamentous fungi produce a diverse array of secondary metabolites--small molecules that are not necessary for normal growth or development. Secondary metabolites have a tremendous impact on society; some are exploited for their antibiotic and pharmaceutical activities, others are involved in disease interactions with plants or animals. The availability of fungal genome sequences has led to an enhanced effort at identifying biosynthetic genes for these molecules. Genes that regulate production of secondary metabolites have been identified and a link between secondary metabolism, light and sexual/asexual reproduction established. However, the role of secondary metabolites in the fungi that produce them remains a mystery. Many of these fungi live saprophytically in the soil and such molecules may provide protection against other inhabitants in this ecological niche.     

The Influence of Environmental Conditions on Secondary Metabolites in Medicinal Plants: A Literature Review

Medicinal plants, a source of different phytochemical compounds, are now subjected to a variety of environmental stresses during their growth and development. Different ecologically limiting factors including temperature, carbon dioxide, lighting, ozone, soil water, soil salinity and soil fertility has significant impact on medicinal plants′ physiological and biochemical responses, as well as the secondary metabolic process. Secondary metabolites (SMs) are useful for assessing the quality of therapeutic ingredients and nowadays, these are used as important natural derived drugs such as immune suppressant, antibiotics, anti-diabetic, and anti-cancer. Plants have the ability to synthesize a variety of secondary metabolites to cope with the negative effects of stress. Here, we focus on how individual environmental variables influence the accumulation of plant secondary metabolites. A total of 48 articles were found to be relevant to the review topic during our systematic review. The review showed the influence of different environmental variables on SMs production and accumulation is complex suggesting the relationship are not only species-specific but also related to increases and decline in SMs by up to 50 %. Therefore, this review improves our understanding of plant SMs ability to adapt to key environmental factors. This can aid in the efficient and long-term optimization of cultivation techniques under ambient environmental conditions in order to maximize the quality and quantity of SMs in plants.     

Unexpected applications of secondary metabolites

Secondary metabolites have been found to have interesting applications over and above their well-known medical uses, e.g., as antimicrobials, etc. These alternative applications include antitumor, cholesterol-lowering, immunosuppressant, antiprotozoal, antihelminth, antiviral and anti-ageing activities. Polyene antibiotics, such as amphotericin B, are of use as antiprion agents, antitumor drugs and against leishmaniasis. Other microbial natural products that show antibiotic activity are used against cancer e.g., doxorubicin, neomycin, β-lactams, bleomycin and rapamycin. Macrolide antibiotics, such as erythromycin, clarithromycin and azithromycin, improve pulmonary function in patients suffering from panbion cholitis. Pigments like prodigiosin and shikonin have antitumor activity, while violacein has anti-ulcer and antitumor activity and also acts as an antiprotozoal agent. Statins, in addition to lowering cholesterol and LDL levels, also decrease elevated C-reactive protein (CRP) levels independent of their cholesterol effects. Immunosppressants have many alternative effects: (i) Cyclosporin is proving useful in treatment of inflammatory disease such as asthma and muscular dystrophy. (ii) Rapamycin is extremely useful in preventing restenosis of stents grafted in balloon angioplasty. (iii) Tacrolimus and ascomycin help in treating inflammatory skin disease such as allergic contact dermatitis and psoriasis. Artemisinin, an antimalarial agent, is also showing antitumor activity. Other natural products, including those from plants (betulinic acid and shikonin), animals (bryostatins) and microbes (squalestatin and sophorolipids) have a multiplicity of potentially useful actions. Unexpected functions of known secondary metabolites are continuously being unraveled, and are fulfilling some of the needs of present day medicine and show great promise for the future.     

Role of Secondary Metabolites and Brassinosteroids in Plant Defense Against Environmental Stresses

Being sessile, plants are subjected to a diverse array of environmental stresses during their life span. Exposure of plants to environmental stresses results in the generation of reactive oxygen species (ROS). These activated oxygen species tend to oxidize various cellular biomolecules like proteins, nucleic acids, and lipids, a process that challenges the core existence of the cell. To prevent the accumulation of these ROS and to sustain their own survival, plants have developed an intricate antioxidative defence system. The antioxidative defence system comprises various enzymatic and nonenzymatic molecules, produced to counter the adverse effect of environmental stresses. A sizable number of these molecules belong to the category of compounds called secondary metabolites. Secondary metabolites are organic compounds that are not directly involved in the growth and development of plants but perform specialized functions under a given set of conditions. Absence of secondary metabolites results in long-term impairment of the plant’s survivability. Such compounds generally include pigments, phenolics, and so on. Plant phenolic compounds such as flavonoids and lignin precursors have been reported to accumulate in response to various biotic and abiotic stresses and are regarded as crucial defence compounds that can scavenge harmful ROS. Another important category of plant metabolites, called brassinosteroids, exhibit stress regulatory and growth-promoting activity and are classified as phytohormones. Elucidation of the physiological and molecular effects of secondary metabolites and brassinosteroids have catapulted them as highly promising and environment-friendly natural substances, suitable for wider application in plant protection and crop yield promotion. The present review focuses on our current understanding of how plants respond to the generation of excessive ROS and the role of secondary metabolites and brassinosteroids in countering the adverse effects of environmental stresses.     

Improvement of hairy root cultures and plants by changing biosynthetic pathways leading to pharmaceutical metabolites: Strategies and applications

A plethora of bioactive plant metabolites has been explored for pharmaceutical, food chemistry and agricultural applications. The chemical synthesis of these structures is often difficult, so plants are favorably used as producers. While whole plants can serve as a source for secondary metabolites and can be also improved by metabolic engineering, more often cell or organ cultures of relevant plant species are of interest. It should be noted that only in few cases the production for commercial application in such cultures has been achieved. Their genetic manipulation is sometimes faster and the production of a specific metabolite is more reliable, because of less environmental influences. In addition, upscaling in bioreactors is nowadays possible for many of these cultures, so some are already used in industry. There are approaches to alter the profile of metabolites not only by using plant genes, but also by using bacterial genes encoding modifying enzymes. Also, strategies to cope with unwanted or even toxic compounds are available. The need for metabolic engineering of plant secondary metabolite pathways is increasing with the rising demand for (novel) compounds with new bioactive properties. Here, we give some examples of recent developments for the metabolic engineering of plants and organ cultures, which can be used in the production of metabolites with interesting properties.     

Total biosynthesis of antitumor nonribosomal peptides in Escherichia coli

Nonribosomal peptides (NRPs) are a class of microbial secondary metabolites that have a wide variety of medicinally important biological activities, such as antibiotic (vancomycin), immunosuppressive (cyclosporin A), antiviral (luzopeptin A) and antitumor (echinomycin and triostin A) activities. However, many microbes are not amenable to cultivation and require time-consuming empirical optimization of incubation conditions for mass production of desired secondary metabolites for clinical and commercial use. Therefore, a fast, simple system for heterologous production of natural products is much desired. Here we show the first example of the de novo total biosynthesis of biologically active forms of heterologous NRPs in Escherichia coli. Our system can serve not only as an effective and flexible platform for large-scale preparation of natural products from simple carbon and nitrogen sources, but also as a general tool for detailed characterizations and rapid engineering of biosynthetic pathways for microbial syntheses of novel compounds and their analogs.     

bZIP转录因子调控植物次生代谢产物生物合成的研究进展

植物次生代谢产物是通过次生代谢产生的一类小分子有机化合物,是植物适应环境的表现,次生代谢产物也是重要药物和化工原料的来源。bZIP转录因子是普遍存在于真核生物中的一类多基因家族,可有效调控植物次生代谢产物的生物合成。本文概述了植物bZIP转录因子的结构和类型,重点阐述了bZIP转录因子调控萜类、黄酮类和生物碱等植物次生代谢产物生物合成的研究进展,并对研究前景进行了展望。深入探讨bZIP转录因子的调控机制,有助于利用基因工程技术优化植物次生代谢途径,提高次生代谢产物的含量,在新药创制、工农业生产等方面具有广泛的应用前景。     

次生代谢产物与植物抗病防御反应

次生代谢产物是由植物次生代谢产生的许多结构不同的小分子有机化合物,它们广泛参与植物的生长、发育、防御等生理过程。次生代谢产物在植物的抗病防御反应中发挥着重要作用,可以作为生化壁垒防御病原物侵染,还可以作为信号物质参与植物的抗病反应;在植物与病原物互作中,植物合成新的抗菌物质植保素,原有的抗菌物质也会增加。植物次生代谢产物的积累受到病原物、发育,环境等多种因素的调节。本文重点介绍次生代谢产物在植物抗病防御中的相关作用以及影响其合成的各种因素。     

Aspergillus nidulans Synthesize Insect Juvenile Hormones upon Expression of a Heterologous Regulatory Protein and in Response to Grazing by Drosophila melanogaster Larvae

Secondary metabolites are known to serve a wide range of specialized functions including communication, developmental control and defense. Genome sequencing of several fungal model species revealed that the majority of predicted secondary metabolite related genes are silent in laboratory strains, indicating that fungal secondary metabolites remain an underexplored resource of bioactive molecules. In this study, we combine heterologous expression of regulatory proteins in Aspergillus nidulans with systematic variation of growth conditions and observe induced synthesis of insect juvenile hormone-III and methyl farnesoate. Both compounds are sesquiterpenes belonging to the juvenile hormone class. Juvenile hormones regulate developmental and metabolic processes in insects and crustaceans, but have not previously been reported as fungal metabolites. We found that feeding by Drosophila melanogaster larvae induced synthesis of juvenile hormone in A. nidulans indicating a possible role of juvenile hormone biosynthesis in affecting fungal-insect antagonisms.     

Metabolomic analysis reveals reliance on secondary plant metabolites to facilitate carnivory in the Cape sundew,Drosera capensis

Background and AimsSecondary metabolites are integral to multiple key plant processes (growth regulation, pollinator attraction and interactions with conspecifics, competitors and symbionts) yet their role in plant adaptation remains an underexplored area of research. Carnivorous plants use secondary metabolites to acquire nutrients from prey, but the extent of the role of secondary metabolites in plant carnivory is not known. We aimed to determine the extent of the role of secondary metabolites in facilitating carnivory of the Cape sundew, Drosera capensis.MethodsWe conducted metabolomic analysis of 72 plants in a time-series experiment before and after simulated prey capture. We used ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) and the retention time index to identify compounds in the leaf trap tissue that changed up to 72 h following simulated prey capture. We identified associated metabolic pathways, and cross-compared these compounds with metabolites previously known to be involved in carnivorous plants across taxa.Key ResultsFor the first time in a carnivorous plant, we have profiled the whole-leaf metabolome response to prey capture. Reliance on secondary plant metabolites was higher than previously thought – 2383 out of 3257 compounds in fed leaves had statistically significant concentration changes in comparison with unfed controls. Of these, ~34 compounds are also associated with carnivory in other species; 11 are unique to Nepenthales. At least 20 compounds had 10-fold changes in concentration, 12 of which had 30-fold changes and are typically associated with defence or attraction in non-carnivorous plants.ConclusionsSecondary plant metabolites are utilized in plant carnivory to an extent greater than previously thought – we found a whole-metabolome response to prey capture. Plant carnivory, at the metabolic level, likely evolved from at least two distinct functions: attraction and defence. Findings of this study support the hypothesis that secondary metabolites play an important role in plant diversification and adaptation to new environments.