LC/MS profiling of flavonoid glycoconjugates isolated from hairy roots, suspension root cell cultures and seedling roots of Medicago truncatula

Hairy Root Cultures as a Source of Polyphenolic Antioxidants: Flavonoids, Stilbenoids and Hydrolyzable Tannins

Due to their chemical properties and biological activity, antioxidants of plant origin have gained interest as valuable components of the human diet, potential food preservatives and additives, ingredients of cosmetics and factors implicated in tolerance mechanisms against environmental stress. Plant polyphenols are the most prominent and extensively studied, albeit not only group of, secondary plant (specialized) metabolites manifesting antioxidative activity. Because of their potential economic importance, the productive and renewable sources of the compounds are desirable. Over thirty years of research on hairy root cultures, as both producers of secondary plant metabolites and experimental systems to investigate plant biosynthetic pathways, brought about several spectacular achievements. The present review focuses on the Rhizobium rhizogenes-transformed roots that either may be efficient sources of plant-derived antioxidants or were used to elucidate some regulatory mechanisms responsible for the enhanced accumulation of antioxidants in plant tissues.

Flavonoid Accumulation Varies in Medicago truncatula in Response to Mercury Stress

Mercury (Hg) contamination is increasing worldwide in both wild ecosystems and agricultural soils due to natural processes, but mostly to anthropic activities. The molecular mechanisms involved in Hg toxicity and tolerance in plants have been extensively studied; however, the role of flavonoids in response to Hg stress remains to be investigated. We conducted a metabolomic study to analyze the changes induced at the secondary metabolite level in three Hg-tolerant and one Hg-sensitive Medicago truncatula cultivars. A total of 46 flavonoid compounds, classified into five different flavonoid families: anthocyanidins, flavones, isoflavones, pterocarpan flavonoids, and flavanones, along with their respective glycoconjugate derivatives, were identified in leaf and root tissues. The synthesis of free isoflavones, followed by monoglycosylation and further malonylation was shown to be characteristic of root samples, whereas higher glycosylation, followed by further acylation with coumaric and ferulic acid was characteristic of leaf tissues. While minor changes were observed in leaves, significant quantitative changes could be observed in roots upon Hg treatment. Some flavonoids were strongly upregulated in roots, including malonylglucosides of biochanin A, formononetin and medicarpin, and aglycones biochanin, daidzein, and irisolidone. Hg tolerance appeared to be mainly associated to the accumulation of formononetin MalGlc, tricin GlcAGlcA, and afrormosin Glc II in leaves, whereas aglycone accumulation was associated with tolerance to Hg stress in roots. The results evidence the alteration of the flavonoid metabolic profile and their glycosylation processes in response to Hg stress. However, notable differences existed between varieties, both in the basal metabolic profile and in the response to treatment with Hg. Overall, we observed an increase in flavonoid production in response to Hg stress, and Hg tolerance appeared to be associated to a characteristic glycosylation pattern in roots, associated with the accumulation of aglycones and monoglycosylated flavonoids. The findings are discussed in the context of the flavonoid biosynthetic pathway to provide a better understanding of the role of these secondary metabolites in the response and tolerance to Hg stress in M. truncatula.

Identification of an Isoflavonoid Transporter Required for the Nodule Establishment of the Rhizobium-Fabaceae Symbiotic Interaction

Nitrogen (N) as well as Phosphorus (P) are key nutrients determining crop productivity. Legumes have developed strategies to overcome nutrient limitation by, for example, forming a symbiotic relationship with N-fixing rhizobia and the release of P-mobilizing exudates and are thus able to grow without supply of N or P fertilizers. The legume-rhizobial symbiosis starts with root release of isoflavonoids that act as signaling molecules perceived by compatible bacteria. Subsequently, bacteria release nod factors, which induce signaling cascades allowing the formation of functional N-fixing nodules. We report here the identification and functional characterization of a plasma membrane-localized MATE-type transporter (LaMATE2) involved in the release of genistein from white lupin roots. The LaMATE2 expression in the root is upregulated under N deficiency as well as low phosphate availability, two nutritional deficiencies that induce the release of this isoflavonoid. LaMATE2 silencing reduced genistein efflux and even more the formation of symbiotic nodules, supporting the crucial role of LaMATE2 in isoflavonoid release and nodulation. Furthermore, silencing of LaMATE2 limited the P-solubilization activity of lupin root exudates. Transport assays in yeast vesicles demonstrated that LaMATE2 acts as a proton-driven isoflavonoid transporter.

UGT84F9 is the major flavonoid UDP-glucuronosyltransferase in Medicago truncatula

Mammalian phase II metabolism of dietary plant flavonoid compounds generally involves substitution with glucuronic acid. In contrast, flavonoids mainly exist as glucose conjugates in plants, and few plant UDP-glucuronosyltransferase enzymes have been identified to date. In the model legume Medicago truncatula, the major flavonoid compounds in the aerial parts of the plant are glucuronides of the flavones apigenin and luteolin. Here we show that the M. truncatula glycosyltransferase UGT84F9 is a bi-functional glucosyl/glucuronosyl transferase in vitro, with activity against a wide range of flavonoid acceptor molecules including flavones. However, analysis of metabolite profiles in leaves and roots of M. truncatula ugt84f9 loss of function mutants revealed that the enzyme is essential for formation of flavonoid glucuronides, but not most flavonoid glucosides, in planta. We discuss the use of plant UGATs for the semi-synthesis of flavonoid phase II metabolites for clinical studies.

Isoflavonoid biosynthesis in cultivated and wild soybeans grown in the field under adverse climate conditions

The cultivation of soybean plants is one of the most important crop production sectors in the world. Isoflavones are an important defence against pathogens in soybeans. The aim of the present study was to analyse isoflavone biosynthesis in wild and cultivated soybeans grown in the field conditions in an unfavourable climate. We analysed by LCMS-IT-TOF the composition and content of isoflavonoids, productivity and fungal disease resistance of wild and cultivated. The Hefeng25 and Sfera varieties have the highest isoflavonoid content and fungal tolerance. We have shown a 3-fold increase of total isoflavonoids in Sfera, comparing with wild type, and 4- and 7-fold increases of total isoflavone aglycones in Hefeng25 and Sfera, respectively. Accordingly, the expression of genes encoding enzymes of the isoflavonoid biosynthetic pathway was also maximal in these cultivars. Thus, biosynthetic status is an important indicator of soybean productivity and resistance to pathogens in adverse climates.

Long-Term Cd Exposure Alters the Metabolite Profile in Stem Tissue of Medicago sativa

As a common pollutant, cadmium (Cd) is one of the most toxic heavy metals accumulating in agricultural soils through anthropogenic activities. The uptake of Cd by plants is the main entry route into the human food chain, whilst in plants it elicits oxidative stress by unbalancing the cellular redox status. Medicago sativa was subjected to chronic Cd stress for five months. Targeted and untargeted metabolic analyses were performed. Long-term Cd exposure altered the amino acid composition with levels of asparagine, histidine and proline decreasing in stems but increasing in leaves. This suggests tissue-specific metabolic stress responses, which are often not considered in environmental studies focused on leaves. In stem tissue, profiles of secondary metabolites were clearly separated between control and Cd-exposed plants. Fifty-one secondary metabolites were identified that changed significantly upon Cd exposure, of which the majority are (iso)flavonoid conjugates. Cadmium exposure stimulated the phenylpropanoid pathway that led to the accumulation of secondary metabolites in stems rather than cell wall lignification. Those metabolites are antioxidants mitigating oxidative stress and preventing cellular damage. By an adequate adjustment of its metabolic composition, M. sativa reaches a new steady state, which enables the plant to acclimate under chronic Cd stress.

Convergent recruitment of 5'-hydroxylase activities by CYP75B flavonoid B-ring hydroxylases for tricin biosynthesis in Medicago legumes

Tricin (3',5'-dimethoxylated flavone) is a predominant flavonoid amongst monocots but occurs only in isolated and unrelated dicot lineages. Although tricin biosynthesis has been intensively studied in monocots, it has remained largely elusive in tricin-accumulating dicots. We investigated a subgroup of cytochrome P450 (CYP) 75B subfamily flavonoid B-ring hydroxylases (FBHs) from two tricin-accumulating legumes, Medicago truncatula and alfalfa (Medicago sativa), by phylogenetic, molecular, biochemical and mutant analyses. Five Medicago cytochrome P450 CYP75B FBHs are phylogenetically distant from other legume CYP75B members. Among them, MtFBH-4, MsFBH-4 and MsFBH-10 were expressed in tricin-accumulating vegetative tissues. In vitro and in planta analyses demonstrated that these proteins catalyze 3'- and 5'-hydroxylations critical to tricin biosynthesis. A key amino acid polymorphism, T492G, at their substrate recognition site 6 domain is required for the novel 5'-hydroxylation activities. Medicago truncatula mtfbh-4 mutants were tricin-deficient, indicating that MtFBH-4 is indispensable for tricin biosynthesis. Our results revealed that these Medicago legumes had acquired the tricin pathway through molecular evolution of CYP75B FBHs subsequent to speciation from other nontricin-accumulating legumes. Moreover, their evolution is independent of that of grass-specific CYP75B apigenin 3'-hydroxylases/chrysoeriol 5'-hydroxylases dedicated to tricin production and Asteraceae CYP75B flavonoid 3',5'-hydroxylases catalyzing the production of delphinidin-based pigments.

Metabolomic Determination of Specialized Metabolites Using Liquid Chromatography-Tandem Mass Spectrometry in the Traditional Chinese Medicines Astragali Radix and Hedysari Radix

The Traditional Chinese Medicines (TCMs) Astragali Radix (AR) derived from Astragalus membranaceus (Fisch.) Bge. var. mongholicus (Bge.) Hsiao and A. membranaceus (Fisch.) Bge., and Hedysari Radix (HR) derived from Hedysarum polybotrys Hand.-Mazz. (family Leguminosae) are well-known for increasing the tonic effects on “Qi.” A better insight into the specialized (secondary) metabolites is essential to understand the effects of TCM; however, such metabolites remain largely unknown. Here, we performed a metabolomics-based analysis using liquid chromatography-tandem mass spectrometry in 3 plant tissues—periderm, phloem, and xylem—to identify potential bioactive metabolites. Multivariate statistical analysis revealed 29 metabolites showing a significant difference between groups and 10 biomarker candidates of AR and HR. An anti-inflammatory assay showed that the xylem of both AR and HR and the phloem of HR showed higher anti-inflammatory activity than the positive control quercetin in terms of nitric oxide inhibition.

MtABCG20 is an ABA exporter influencing root morphology and seed germination of Medicago truncatula

Abscisic acid (ABA) integrates internal and external signals to coordinate plant development, growth and architecture. It plays a central role in stomatal closure, and prevents germination of freshly produced seeds and germination of non-dormant seeds under unfavorable circumstances. Here, we describe a Medicago truncatula ATP-binding cassette (ABC) transporter, MtABCG20, as an ABA exporter present in roots and germinating seeds. In seeds, MtABCG20 was found in the hypocotyl-radicle transition zone of the embryonic axis. Seeds of mtabcg20 plants were more sensitive to ABA upon germination, due to the fact that ABA translocation within mtabcg20 embryos was impaired. Additionally, the mtabcg20 produced fewer lateral roots and formed more nodules compared with wild-type plants in conditions mimicking drought stress. Heterologous expression in Arabidopsis thaliana provided evidence that MtABCG20 is a plasma membrane protein that is likely to form homodimers. Moreover, export of ABA from Nicotiana tabacum BY2 cells expressing MtABCG20 was faster than in the BY2 without MtABCG20. Our results have implications both in legume crop research and determination of the fundamental molecular processes involved in drought response and germination.

Distinctive Patterns of Flavonoid Biosynthesis in Roots and Nodules of Datisca glomerata and Medicago spp. Revealed by Metabolomic and Gene Expression Profiles

Plants within the Nitrogen-fixing Clade (NFC) of Angiosperms form root nodule symbioses with nitrogen-fixing bacteria. Actinorhizal plants (in Cucurbitales, Fagales, Rosales) form symbioses with the actinobacteria Frankia while legumes (Fabales) form symbioses with proteobacterial rhizobia. Flavonoids, secondary metabolites of the phenylpropanoid pathway, have been shown to play major roles in legume root nodule symbioses: as signal molecules that in turn trigger rhizobial nodulation initiation signals and acting as polar auxin transport inhibitors, enabling a key step in nodule organogenesis. To explore a potentially broader role for flavonoids in root nodule symbioses across the NFC, we combined metabolomic and transcriptomic analyses of roots and nodules of the actinorhizal host Datisca glomerata and legumes of the genus Medicago. Patterns of biosynthetic pathways were inferred from flavonoid metabolite profiles and phenylpropanoid gene expression patterns in the two hosts to identify similarities and differences. Similar classes of flavonoids were represented in both hosts, and an increase in flavonoids generally in the nodules was observed, with differences in flavonoids prominent in each host. While both hosts produced derivatives of naringenin, the metabolite profile in D. glomerata indicated an emphasis on the pinocembrin biosynthetic pathway, and an abundance of flavonols with potential roles in symbiosis. Additionally, the gene expression profile indicated a decrease in expression in the lignin/monolignol pathway. In Medicago sativa, by contrast, isoflavonoids were highly abundant featuring more diverse and derived isoflavonoids than D. glomerata. Gene expression patterns supported these differences in metabolic pathways, especially evident in a difference in expression of cinnamic acid 4-hydroxylase (C4H), which was expressed at substantially lower levels in D. glomerata than in a Medicago truncatula transcriptome where it was highly expressed. C4H is a major rate-limiting step in phenylpropanoid biosynthesis that separates the pinocembrin pathway from the lignin/monolignol and naringenin-based flavonoid branches. Shikimate O-hydroxycinnamoyltransferase, the link between flavonoid biosynthesis and the lignin/monolignol pathway, was also expressed at much lower levels in D. glomerata than in M. truncatula. Our results indicate (a) a likely major role for flavonoids in actinorhizal nodules, and (b) differences in metabolic flux in flavonoid and phenylpropanoid biosynthesis between the different hosts in symbiosis.

A comparative study of biotechnological approaches for producing valuable flavonoids in Prosopis farcta

The callus and hairy root cultures of Prosopis farcta were established to develop effective strategies to enhance its valuable and medicinally important flavonoid compounds. For callus induction, the hypocotyl, cotyledon and shoot explants were subjected to different plant hormones, naphthalene acetic acid (NAA), benzylaminopurine (BAP), kinetin and dichlorophenoxyacetic acid (2,4-D). Greater callus induction was obtained from hypocotyl explants on MS medium containing 3.0 mg L^-1 NAA + 2.0 mg L^-1 BAP. With the addition of 0.5 mg L^-1 asparagine to this medium, the maximum callus growth was achieved. Hairy root culture of P. farcta was performed using transformation of different explants with strains of Agrobacterium rhizogenes LBA9404, A4, AR15834. The AR15834 strain was more effective for hairy root induction where it caused hairy root formation on 59% of the infected cotyledon explants. We compared profiles of flavonoids isolated from seedling roots, hairy roots, and callus cultures of P. farcta. The colorimetric analysis showed that the content of total flavonoids of hairy roots was 1.54 and 2.52 times higher than in seedling roots and callus, respectively. The presence of flavonoids was verified by LC/MS in positive ion mode. The results showed that flavonoid composition was different in the roots and callus. Naringenin was the major constituent in callus, whereas resveratrol, quercetin and myricetin were the most abundant compounds found in hairy roots. The main objective of this research was to establish hairy roots in P. farcta to synthesize flavonoids at levels comparable to in vitro-grown roots. The present study also opens up a way to further improve the production of pharmaceutically valuable flavonoids and to produce desired metabolites using the hairy root culture system.

Characterization of UGT716A1 as a Multi-substrate UDP:Flavonoid Glucosyltransferase Gene in Ginkgo biloba

Ginkgo biloba L., a "living fossil" and medicinal plant, is a well-known rich source of bioactive flavonoids. The molecular mechanism underlying the biosynthesis of flavonoid glucosides, the predominant flavonoids in G. biloba, remains unclear. To better understand flavonoid glucosylation in G. biloba, we generated a transcriptomic dataset of G. biloba leaf tissue by high-throughput RNA sequencing. We identified 25 putative UDP-glycosyltransferase (UGT) unigenes that are potentially involved in the flavonoid glycosylation. Among them, we successfully isolated and expressed eight UGT genes in Escherichia coli, and found that recombinant UGT716A1 protein was active toward broad range of flavonoid/phenylpropanoid substrates. In particular, we discovered the first recombinant UGT protein, UGT716A1 from G. biloba, possessing unique activity toward flavanol gallates that have been extensively documented to have significant bioactivity relating to human health. UGT716A1 expression level paralleled the flavonoid distribution pattern in G. biloba. Ectopic over-expression of UGT716A1 in Arabidopsis thaliana led to increased accumulation of several flavonol glucosides. Identification and comparison of the in vitro enzymatic activity of UGT716A1 homologs revealed a UGT from the primitive land species Physcomitrella patens also showed broader substrate spectrum than those from higher plants A. thaliana, Vitis vinifera, and Medicago truncatula. The characterization of UGT716A1 from G. biloba bridges a gap in the evolutionary history of UGTs in gymnosperms. We also discuss the implication of UGT716A1 for biosynthesis, evolution, and bioengineering of diverse glucosylated flavonoids.

Medicago truncatula ABCG10 is a transporter of 4-coumarate and liquiritigenin in the medicarpin biosynthetic pathway

The ABCG10 protein of the model legume Medicago truncatula is required for efficient de novo production of the phenylpropanoid-derived phytoalexin medicarpin. Silencing the expression of MtABCG10 results, inter alia, in a lower accumulation of medicarpin and its precursors. In this study, we demonstrate that the impairment of medicarpin biosynthesis can be partially averted by the exogenous application of 4-coumarate, an early precursor of the core phenylpropanoid pathway, and the deoxyisoflavonoid formononetin. Experiments conducted using HPLC/MS in a heterologous system as well as in vitro transport assays with labelled substrate revealed that MtABCG10 is responsible for the membrane translocation of 4-coumarate and liquiritigenin, molecules representing key branching points in the phenylpropanoid pathway. The identification of transporters participating in the distribution of precursors is an important step in understanding phenylpropanoid biosynthesis.

PlantMAT: A Metabolomics Tool for Predicting the Specialized Metabolic Potential of a System and for Large-Scale Metabolite Identifications

Custom software entitled Plant Metabolite Annotation Toolbox (PlantMAT) has been developed to address the number one grand challenge in metabolomics, which is the large-scale and confident identification of metabolites. PlantMAT uses informed phytochemical knowledge for the prediction of plant natural products such as saponins and glycosylated flavonoids through combinatorial enumeration of aglycone, glycosyl, and acyl subunits. Many of the predicted structures have yet to be characterized and are absent from traditional chemical databases, but have a higher probability of being present in planta. PlantMAT allows users to operate an automated and streamlined workflow for metabolite annotation from a user-friendly interface within Microsoft Excel, a familiar, easily accessed program for chemists and biologists. The usefulness of PlantMAT is exemplified using ultrahigh-performance liquid chromatography-electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UHPLC-ESI-QTOF-MS/MS) metabolite profiling data of saponins and glycosylated flavonoids from the model legume Medicago truncatula. The results demonstrate PlantMAT substantially increases the chemical/metabolic space of traditional chemical databases. Ten of the PlantMAT-predicted identifications were validated and confirmed through the isolation of the compounds using ultrahigh-performance liquid chromatography-mass spectrometry-solid-phase extraction (UHPLC-MS-SPE) followed by de novo structural elucidation using 1D/2D nuclear magnetic resonance (NMR). It is further demonstrated that PlantMAT enables the dereplication of previously identified metabolites and is also a powerful tool for the discovery of structurally novel metabolites.

Bioactivity of Diterpens from the Ethyl Acetate Extract of Kingiodendron pinnatum Rox. Hams

Background:

Kingiodendron pinnatum Rox. Hams. is an endangered medicinal plant used in gonorrhoe, catarrhal conditions of genito-urinary and respiratory tracts. The scientific and pharmacological formulation of K. pinnatum has not been established so far though it is being traditionally used by tribes of the region.

Objective:

P hytochemical screening and identification of the bioactive compounds from the ethyl acetate extract of Kingiodendron pinnatum Rox. Hams.

Materials and Methods:

Chromatographic separation was carried out by thin layer chromatography and column chromatography. Bio-autography of the column fractioned extract and TLC chromatogram were evaluated in vitro for antibacterial activity. The PTLC, HP TLC were used for crude extract and HPLC, LCMS, FTIR, ¹HNMR and ¹³CNMR were employed for the isolated compound in the ethyl acetate extract of K. pinnatum.

Results:

Evaluation of solvent system for chromatographic separation revealed that ethyl acetate: petroleum ether in the ratio of 7:2.5 ml was the most appropriate one for the separation of diterpene compounds. The antibacterial bio-autography screening of TLC separated compound showed positive activity with Staphylococcus aureus and negative activity with Escherichia coli. Spectroscopic analysis of the isolated compound from the ethyl acetate extract of K. pinnatum revealed the presence of diterpene compound.

Conclusion:

It is evident from the present study that the ethyl acetate extract of K. pinnatum is rich in diterpene compounds and having potential antibacterial activity.

SUMMARY

Novel extraction method for phytochemicls from Kingidendron pinnatum at RT

Antibacterial property of diterpens extracted from Kingiodendron pinnatum Rox. Hams aganist S. aureus

Abbreviations Used: TLC: Thin Layer Chromatography, PTLC: Preparatory Thin Layer Chromatography, HPTLC: High perormence Thin Layer chromatography, HPLC: High Performance Liquid Chromatography, LC-MS: Liquid chromatography Mass Spectra, FTIR: Fourier Transform Infrared Chromatography, NMR: Nuclear Magnetic Resonance

Amelioratory effect of flavonoids rich Pergularia daemia extract against CFA induced arthritic rats

PURPOSE

Pergularia daemia Forsk. (Asclepiadaceae) is a traditionally reported medicinal herb used to treat joint pain and arthritis. However, there are no scientific reports about anti-arthritic activity of P. daemia methanolic extract on rats as animal model. This study identifies bioactive compounds present in the P. daemia methanolic extract and evaluates its anti-arthritic potential in CFA induced arthritic rats.

METHODS AND RESULTS

Phytoconstituents of P. daemia extract were examined using LC-ESI/MS method. Anti-arthritic activity of P. daemia extract was determined by various biochemical experiments (RF, ESR and CRP), ultrasonography and histological analysis. LC-ESI/MS analysis resulted in the identification of major flavonoids compounds such as formononetin, qurecetin, chrysoeriol, taxifolin and naringenin. Serum biomarker analysis, after the treatment with PDME (500mg/kg b.w.) revealed that the hemoglobin (11.84±0.42g/dL) and RBC (8.38±0.67million/mm(3)) levels were significantly increased whereas WBC (8.91±0.38thousands/mm(3)), RF (17.94±0.45IU/mL), ESR (7.91±0.12mm/h) and CRP (22.56±0.26mg/L) levels were decreased when compared with the CFA induced arthritic control group. Histology results revealed that treatment with PDME has resulted in significant prevention against bony destruction by decreasing soft tissue swelling and narrowing of joint spaces (250 and 500mg/kg b.w.).

CONCLUSION

Anti-arthritic effect of P. daemia might be due to the presence of these bioactive flavonoids. These findings lend pharmacological support to the reported folkloric use of P. daemia in the treatment and management of painful, arthritic inflammatory conditions.

Proteomics and Metabolomics: Two Emerging Areas for Legume Improvement

The crop legumes such as chickpea, common bean, cowpea, peanut, pigeonpea, soybean, etc. are important sources of nutrition and contribute to a significant amount of biological nitrogen fixation (>20 million tons of fixed nitrogen) in agriculture. However, the production of legumes is constrained due to abiotic and biotic stresses. It is therefore imperative to understand the molecular mechanisms of plant response to different stresses and identify key candidate genes regulating tolerance which can be deployed in breeding programs. The information obtained from transcriptomics has facilitated the identification of candidate genes for the given trait of interest and utilizing them in crop breeding programs to improve stress tolerance. However, the mechanisms of stress tolerance are complex due to the influence of multi-genes and post-transcriptional regulations. Furthermore, stress conditions greatly affect gene expression which in turn causes modifications in the composition of plant proteomes and metabolomes. Therefore, functional genomics involving various proteomics and metabolomics approaches have been obligatory for understanding plant stress tolerance. These approaches have also been found useful to unravel different pathways related to plant and seed development as well as symbiosis. Proteome and metabolome profiling using high-throughput based systems have been extensively applied in the model legume species, Medicago truncatula and Lotus japonicus, as well as in the model crop legume, soybean, to examine stress signaling pathways, cellular and developmental processes and nodule symbiosis. Moreover, the availability of protein reference maps as well as proteomics and metabolomics databases greatly support research and understanding of various biological processes in legumes. Protein-protein interaction techniques, particularly the yeast two-hybrid system have been advantageous for studying symbiosis and stress signaling in legumes. In this review, several studies on proteomics and metabolomics in model and crop legumes have been discussed. Additionally, applications of advanced proteomics and metabolomics approaches have also been included in this review for future applications in legume research. The integration of these "omics" approaches will greatly support the identification of accurate biomarkers in legume smart breeding programs.

Expression Analysis of Phenylalanine Ammonia Lyase Gene and Rosmarinic Acid Production in Salvia officinalis and Salvia virgata Shoots Under Salicylic Acid Elicitation

Partial fragments of phenylalanine ammonia lyase (PAL) genes were cloned and characterized from Salvia officinalis (SoPAL) and Salvia virgata (SvPAL). Different concentrations (250 and 500 μM) of exogenous salicylic acid (SA) were used when correlation between PAL expression and rosmarinic acid (RA) accumulation was compared. The results showed that the deduced cDNA sequences of the partial genes had high similarities with those of known PAL gene from other plant species. Semi-quantitative reverse transcription PCR (RT-PCR) analysis revealed that exogenous application of SA led to up-regulating of the PAL expression. Further analysis showed that in S. virgata, at higher concentration of SA, higher accumulation of RA was achieved, while in S. officinalis, the higher RA accumulation was observed at lower concentration of SA. It was concluded that there was no positive correlation between the intensity of PAL transcription and the RA accumulation in the studied species. Therefore, despite of the increase in transcription rate of the PAL at the higher concentration of SA, the lower amounts of RA were accumulated in the case of S. officinalis. Consequently, the hypothesis that PAL is the rate-determining step in RA biosynthesis is not always valid and probably some other unknown factors participate in the synthesis of phenolics.

Mass spectrometric profiling of flavonoid glycoconjugates possessing isomeric aglycones

In fields such as food and nutrition science or plant physiology, interest in untargeted profiling of flavonoids continues to expand. The group of flavonoids encompasses several thousands of chemically distinguishable compounds, among which are a number of isobaric compounds with the same elemental composition. Thus, the mass spectrometric identification of these compounds is challenging, especially when reference standards are not available to support their identification. Many different types of isomers of flavonoid glycoconjugates are known, i.e. compounds that differ in their glycosylation position, glycan sequence or type of interglycosidic linkage. This work focuses on the mass spectrometric identification of flavonoid glycoconjugate isomers possessing the same glycan mass and differing only in their aglycone core. A non-targeted HPLC-ESI-MS/MS profiling method using a triple quadrupole MS is presented herein, which utilizes in-source fragmentation and a pseudo-MS(3) approach for the selective analysis of flavonoid glycoconjugates with isomeric/isobaric aglycones. A selective MRM-based identification of the in-source formed isobaric aglycone fragments was established. Additionally, utilizing the precursor scanning capability of the employed triple quadrupole instrument, the developed method enabled the determination of the molecular weight of the studied intact flavonoid glycoconjugate. The versatility of the method was proven with various types of flavonoid aglycones, i.e. anthocyanins, flavonols, flavones, flavanones and isoflavones, along with their representative glycoconjugates. The developed method was also successfully applied to a commercially available sour cherry sample, in which 16 different glycoconjugates of pelargonidin, genistein, cyanidin, kaempferol and quercetin could be tentatively identified, including a number of compounds containing isomeric/isobaric aglycones.

A generic multiple reaction monitoring based approach for plant flavonoids profiling using a triple quadrupole linear ion trap mass spectrometry

Flavonoids are one of the largest classes of plant secondary metabolites serving a variety of functions in plants and associating with a number of health benefits for humans. Typically, they are co-identified with many other secondary metabolites using untargeted metabolomics. The limited data quality of untargeted workflow calls for a shift from the breadth-first to the depth-first screening strategy when a specific biosynthetic pathway is focused on. Here we introduce a generic multiple reaction monitoring (MRM)-based approach for flavonoids profiling in plants using a hybrid triple quadrupole linear ion trap (QTrap) mass spectrometer. The approach includes four steps: (1) preliminary profiling of major aglycones by multiple ion monitoring triggered enhanced product ion scan (MIM-EPI); (2) glycones profiling by precursor ion triggered EPI scan (PI-EPI) of major aglycones; (3) comprehensive aglycones profiling by combining MIM-EPI and neutral loss triggered EPI scan (NL-EPI) of major glycone; (4) in-depth flavonoids profiling by MRM-EPI with elaborated MRM transitions. Particularly, incorporation of the NH3 loss and sugar elimination proved to be very informative and confirmative for flavonoids screening. This approach was applied for profiling flavonoids in Astragali radix (Huangqi), a famous herb widely used for medicinal and nutritional purposes in China. In total, 421 flavonoids were tentatively characterized, among which less than 40 have been previously reported in this medicinal plant. This MRM-based approach provides versatility and sensitivity that required for flavonoids profiling in plants and serves as a useful tool for plant metabolomics.

Selective responses of enzymes in the two parallel pathways of rosmarinic acid biosynthetic pathway to elicitors in Salvia miltiorrhiza hairy root cultures

Rosmarinic acid and salvianolic acid B are two important phenolic compounds with therapeutic properties in Salvia miltiorrhiza Bunge. The biosynthesis of rosmarinic acid is initiated by two parallel pathways, namely the phenylpropanoid pathway and the tyrosine-derived pathway. Salvianolic acid B is a structural dimer of rosmarinic acid and is believed to be derived from rosmarinic acid. In the current study, methyl jasmonate (MeJA) and hyphal extracts from fungi were used as elicitors to examine the relationship between enzymes in the two parallel pathways and accumulation of phenolic compounds in S. miltiorrhiza hairy root cultures. The results showed that accumulations of rosmarinic acid, salvianolic acid B and total phenolics were enhanced by MeJA while suppressed by fugal extracts. Responses of enzymes in the tyrosine-derived pathway, at both the gene transcript and enzyme activity levels, showed a better consistency with alterations of phenolic compounds content after the two elicitors treated. Our study implied that compared with enzymes in the phenylpropanoid pathway, enzymes in the tyrosine-derived pathway are more correlated to rosmarinic acid and salvianolic acid B biosynthesis in S. miltiorrhiza hairy roots.

Natural product biosynthesis in Medicago species

The genus Medicago, a member of the legume (Fabaceae) family, comprises 87 species of flowering plants, including the forage crop M. sativa (alfalfa) and the model legume M. truncatula (barrel medic). Medicago species synthesize a variety of bioactive natural products that are used to engage into symbiotic interactions but also serve to deter pathogens and herbivores. For humans, these bioactive natural products often possess promising pharmaceutical properties. In this review, we focus on the two most interesting and well characterized secondary metabolite classes found in Medicago species, the triterpene saponins and the flavonoids, with a detailed overview of their biosynthesis, regulation, and profiling methods. Furthermore, their biological role within the plant as well as their potential utility for human health or other applications is discussed. Finally, we give an overview of the advances made in metabolic engineering in Medicago species and how the development of novel molecular and omics toolkits can influence a better understanding of this genus in terms of specialized metabolism and chemistry. Throughout, we critically analyze the current bottlenecks and speculate on future directions and opportunities for research and exploitation of Medicago metabolism.

Combining metabolomics and gene expression analysis reveals that propionyl- and butyryl-carnitines are involved in late stages of arbuscular mycorrhizal symbiosis

The arbuscular mycorrhizal (AM) symbiosis is a widespread mutualistic association between soil fungi (Glomeromycota) and the roots of most plant species. AM fungi are obligate biotrophs whose development is partially under the control of their plant host. We explored the possibility to combine metabolomic and transcriptomic approaches to find putative mycorrhiza-associated metabolites regulating AM fungal development. Methanol extracts of Medicago truncatula roots colonized or not with the AM fungus Rhizophagus irregularis were analyzed and compared by ultra-high-performance liquid chromatography (UHPLC), high-resolution mass spectrometry (Q-TOF), and multivariate statistical discrimination. We detected 71 mycorrhiza-associated analytes exclusively present or at least 10-fold more abundant in mycorrhizal roots. To identify among these analytes those that could regulate AM fungal development, we fractionated by preparative and semi-preparative HPLC the mycorrhizal and non-mycorrhizal root extracts and established how the 71 analytes were distributed among the fractions. Then we tested the activity of the fractions on germinating spores of R. irregularis by quantifying the expression of 96 genes known for their diverse in planta expression patterns. These investigations reveal that propionyl- and butyryl-carnitines accumulated in mycorrhizal roots. The results suggest that these two molecules regulate fungal gene expression in planta and represent interesting candidates for further biological characterization.

Metabolomics in plants and humans: applications in the prevention and diagnosis of diseases

In the recent years, there has been an increase in the number of metabolomic approaches used, in parallel with proteomic and functional genomic studies. The wide variety of chemical types of metabolites available has also accelerated the use of different techniques in the investigation of the metabolome. At present, metabolomics is applied to investigate several human diseases, to improve their diagnosis and prevention, and to design better therapeutic strategies. In addition, metabolomic studies are also being carried out in areas such as toxicology and pharmacology, crop breeding, and plant biotechnology. In this review, we emphasize the use and application of metabolomics in human diseases and plant research to improve human health.

Structural characterization of flavonoid glycosides from leaves of wheat (Triticum aestivum L.) using LC/MS/MS profiling of the target compounds

The aim of this study was to present integrated mass spectrometric methods for the structural characterization and identification of flavonoid glycoconjugates. During the liquid chromatography/mass spectrometry analyses, TriVersa NanoMate chip-based system with nanoelectrospray ionization and fraction collection was combined to a quadrupole time-of-flight mass spectrometer. In the extract samples prepared from green leaves of wheat plantlets, 41 flavonoid derivatives were recognized. Part of the target natural products had the full structure being characterized after the registration of mass spectra, where m/z values for protonated [M + H](+) and deprotonated molecules [M - H](-) were annotated. MS(2) and pseudo-MS(3) experiments were performed for [M + H](+) or [M - H](-) and aglycone ions (Y0(+/-)-type), respectively. It should be underlined that pseudo-MS(3) mass spectra were registered for aglycone product ions in the mass spectra of O-glycosides present in the extract samples. In many cases, only tentative structural identification of aglycones was possible, mainly because of the presence of numerous C-monoglycoside or C-diglycoside in the samples. Acylation of the sugar moiety and/or methylation of the aglycone in the flavonoid glycosides under study was observed. The existence of isobaric and/or isomeric compounds was demonstrated in the extract studied. The collision-induced dissociation mass spectra registered for C,O-diglycosides and C,C-diglycosides did not permit to draw complete structural conclusions about the compounds studied. For the investigated class of natural products, unambiguous classification of sugar moieties linked to the aglycones from the recorded mass spectra was not possible. Registration of the positive and negative ion mass spectra did not lead to the precise conclusion about the glycosylation position at C-6 or C-8, and O-4' or O-7 atoms. It was possible, on the basis of the collected MS(2) spectra, to differentiate between O-glycosides and C-glycosides present in the samples analyzed.

A Medicago truncatula ABC transporter belonging to subfamily G modulates the level of isoflavonoids

Full-sized ATP-binding cassette (ABC) transporters of the G subfamily (ABCG) are considered to be essential components of the plant immune system. These proteins have been proposed to be implicated in the active transmembrane transport of various secondary metabolites. Despite the importance of ABCG-based transport for plant-microbe interactions, these proteins are still poorly recognized in legumes. The experiments described here demonstrated that the level of Medicago truncatula ABCG10 (MtABCG10) mRNA was elevated following application of fungal oligosaccharides to plant roots. Spatial expression pattern analysis with a reporter gene revealed that the MtABCG10 promoter was active in various organs, mostly within their vascular tissues. The corresponding protein was located in the plasma membrane. Silencing of MtABCG10 in hairy roots resulted in lower accumulation of the phenylpropanoid pathway-derived medicarpin and its precursors. PCR-based experiments indicated that infection with Fusarium oxysporum, a root-infecting pathogen, progressed faster in MtABCG10-silenced composite plants (consisting of wild-type shoots on transgenic roots) than in the corresponding controls. Based on the presented data, it is proposed that in Medicago, full-sized ABCG transporters might modulate isoflavonoid levels during the defence response associated with de novo synthesis of phytoalexins.