Changes in the profile of flavonoid accumulation in Medicago truncatula leaves during infection with fungal pathogen Phoma medicaginis

Modulation of defense genes and phenolic compounds in wild blueberry in response to Botrytis cinerea under field conditions

Botrytis blight is an important disease of wild blueberry [(Vaccinium angustifolium (Va) and V. myrtilloides (Vm))] with variable symptoms in the field due to differences in susceptibility among blueberry phenotypes. Representative blueberry plants of varying phenotypes were inoculated with spores of B. cinerea. The relative expression of pathogenesis-related genes (PR3, PR4), flavonoid biosynthesis genes, and estimation of the concentration of ten phenolic compounds between uninoculated and inoculated samples at different time points were analyzed. Representative plants of six phenotypes (brown stem Va, green stem Va, Va f. nigrum, tall, medium, and short stems of Vm) were collected and studied using qRT-PCR. The expression of targeted genes indicated a response of inoculated plants to B. cinerea at either 12, 24, 48 or 96 h post inoculation (hpi). The maximum expression of PR3 occurred at 24 hpi in all the phenotypes except Va f. nigrum and tall stem Vm. Maximum expression of both PR genes occurred at 12 hpi in Va f. nigrum. Chalcone synthase, flavonol synthase and anthocyanin synthase were suppressed at 12 hpi followed by an upregulation at 24 hpi. The expression of flavonoid pathway genes was phenotype-specific with their regulation patterns showing temporal differences among the phenotypes. Phenolic compound accumulation was temporally regulated at different post-inoculation time points. M-coumaric acid and kaempferol-3-glucoside are the compounds that were increased with B. cinerea inoculation. Results from this study suggest that the expression of PR and flavonoid genes, and the accumulation of phenolic compounds associated with B. cinerea infection could be phenotype specific. This study may provide a starting point for understanding and determining the mechanisms governing the wild blueberry-B. cinerea pathosystem.

Do Colletotrichum gloeosporioides and Rhizopus stolonifer induce alkaloidal and antifungal responses in Annona muricata seedlings?

The benzylisoquinoline alkaloids of Annona muricata have been isolated, but their physiological or ecological role is unknown. The objective was to explore whether these secondary metabolites are involved in defense against phytopathogenic fungi. To do this, the alkaloidal response of 6-leaf seedlings of A. muricata was analyzed, previously inoculated with Colletotrichum gloeosporioides and Rhizopus stolonifer. Before and after inoculation, alkaloidal extracts of roots, stems, and leaves were obtained, and the antifungal activity was evaluated in vitro. The alkaloids anonaine, reticuline, nornuciferine, assimilobine, and coreximine were identified. C. gloeosporioides caused variable increases in the production of anonaine, reticuline and nornuciferine (10-1200%), while R. stolonifer only stimulated the increase of nornuciferin and anonaine (10%) in the stems and leaves. The alkaloidal extracts of inoculated seedlings increased the antifungal activity, both against the pathogen elicitor and against the second target pathogen. These findings suggest that the alkaloids participate in the antifungal defense mechanism.

Bisoactive metabolite profile and antioxidant properties of brown juice, a processed Alfalfa (Medicago sativa) by-product

Recently, leaf protein concentrate (LPC) has gained increased attention in response to the constantly growing protein demand. Green biorefineries can become more economical by valorizing their by-products and reducing environmental risks. The current study describes the variations in the antioxidant capacity and phytochemical composition of a liquid by-product (referred to as brown juice (BJ)) obtained during the extraction of leaf protein concentrate (LPC) from the fresh biomass of alfalfa (Medicago sativa L.). Four varieties of alfalfa were investigated during three harvest times, i.e., August 2017 (first harvest), September 2017 (second harvest), and June 2018 (third harvest). Also, the fresh BJ was lacto-fermented to extend its preservation period but also modifying its composition. The results of different general phytochemical composition analyses and antioxidant assays revealed similar tendencies across different alfalfa varieties and harvest times. Most of the phytochemicals in the BJ identified by HPLC-MS/MS can be classified as flavonoids/flavonoid derivatives, e.g., apigenin, naringenin, luteolin, formononetin. Substantially, the lacto-fermentation process induced a switch into aglycones, e.g., apigenin content increased by an order of magnitude, while apigenin-7-O-glucuronide content was halved after lacto-fermentation. Additionally, several B vitamins were detected, including B2, B3, and B7. These results could provide a basis for various ways of industrial valorization but need to be strengthened by data generated from large-scale production.

Functions and biosynthesis of plant signaling metabolites mediating plant-microbe interactions

Covering: 2015-2022Plants and microbes have coevolved since their appearance, and their interactions, to some extent, define plant health. A reasonable fraction of small molecules plants produced are involved in mediating plant-microbe interactions, yet their functions and biosynthesis remain fragmented. The identification of these compounds and their biosynthetic genes will open up avenues for plant fitness improvement by manipulating metabolite-mediated plant-microbe interactions. Herein, we integrate the current knowledge on their chemical structures, bioactivities, and biosynthesis with the view of providing a high-level overview on their biosynthetic origins and evolutionary trajectory, and pinpointing the yet unknown and key enzymatic steps in diverse biosynthetic pathways. We further discuss the theoretical basis and prospects for directing plant signaling metabolite biosynthesis for microbe-aided plant health improvement in the future.

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.

Transcriptome and metabolome profiling in different stages of infestation of Eucalyptus urophylla clones by Ralstonia solanacearum

Eucalyptus urophylla is an economically important tree species that widely planted in tropical and sub-tropical areas around the world, which suffers significant losses due to Ralstonia solanacearum. However, little is known about the molecular mechanism of pathogen-response of Eucalyptus. We collected the vascular tissues of a E. urophylla clone infected by R. solanacearum in the laboratory, and combined transcriptome and metabolome analysis to investigate the defense responses of Eucalyptus. A total of 11 flavonoids that differentially accumulated at the first stage or a later stage after infection. The phenylpropanoid of p-coumaraldehyde, the two alkaloids trigonelline and DL-ephedrine, two types of traditional Chinese medicine with patchouli alcohol and 3-dihydrocadambine, and the amino acid phenylalanine were differentially accumulated after infection, which could be biomarkers indicating a response to R. solanacearum. Differentially expressed genes involved in plant hormone signal transduction, phenylpropanoids, flavonoids, mitogen-activated protein kinase (MAPK) signaling, and amino acid metabolism were activated at the first stage of infection or a later stage, indicating that they may participate in the defense against infection. This study is expected to deliver several insights into the molecular mechanism in response to pathogens in E. urophylla, and the findings have far-reaching implications in the control of E. urophylla pathogens.

From Microns to Meters: Exploring Advances in Legume Microbiome Diversity for Agroecosystem Benefits

Legumes are of primary importance for agroecosystems because they provide protein-rich foods and enhance soil fertility through fixed atmospheric nitrogen. The legume-rhizobia symbiosis that makes this possible has been extensively studied, from basic research on biochemical signaling to practical applications in cropping systems. While rhizobia are the most-studied group of associated microorganisms, the functional benefit they confer to their legume hosts by fixing nitrogen is not performed in isolation. Indeed, non-rhizobia members of the rhizosphere and nodule microbiome are now understood to contribute in multiple ways to nodule formation, legume fitness, and other agroecosystem services. In this review, we summarize advances contributing to our understanding of the diversity and composition of bacterial members of the belowground legume microbiome. We also highlight applied work in legume food and forage crops that link microbial community composition with plant functional benefits. Ultimately, further research will assist in the development of multi-species microbial inoculants and cropping systems that maximize plant nutrient benefits, while reducing sources of agricultural pollution.

Phoma medicaginis Isolate Differences Determine Disease Severity and Phytoestrogen Production in Annual Medicago spp

Phoma black stem and leaf spot disease of annual Medicago spp., caused by Phoma medicaginis, not only can devastate forage and seed yield but can reduce herbage quality by inducing production of phytoestrogens (particularly coumestrol and 4'-O-methylcoumestrol), which can also reduce the ovulation rates of animals grazing infected forage. We determined the consequent phytoestrogen levels on three different annual Medicago species/cultivars (Medicago truncatula cultivar Cyprus, Medicago polymorpha var. brevispina cultivar Serena, and Medicago murex cultivar Zodiac) after inoculation with 35 isolates of P. medicaginis. Across the isolate × cultivar combinations, leaf disease incidence, petiole/stem disease incidence, leaf disease severity, petiole disease severity, and leaf yellowing severity ranged up to 100, 89.4, 100, 58.1, and 61.2%, respectively. Cultivars Cyprus and Serena were the most susceptible and cultivar Zodiac was the most resistant to P. medicaginis. Isolates WAC3653, WAC3658, and WAC4252 produced the most severe disease. Levels of phytoestrogens in stems ranged from 25 to 1,995 mg/kg for coumestrol and from 0 to 418 mg/kg for 4'-O-methylcoumestrol. There was a significant positive relationship of disease incidence and severity parameters with both coumestrol and 4'-O-methylcoumestrol contents, as noted across individual cultivars and across the three cultivars overall, where r = 0.39 and 0.37 for coumestrol and 4'-O-methylcoumestrol, respectively (P < 0.05). Although cultivar Serena was most susceptible to P. medicaginis and produced the highest levels of phytoestrogens in the presence of P. medicaginis, cultivar Zodiac contained the highest levels of phytoestrogens in comparison with other cultivars in the absence of P. medicaginis. There was a 15-fold increase in coumestrol in cultivar Serena but only a 7-fold increase in cultivar Zodiac from infection of P. medicaginis. The study highlights that the intrinsic ability of a particular cultivar to produce phytoestrogens in the absence of the pathogen, and its comparative ability to produce phytoestrogens in the presence of the P. medicaginis, are both important and highly relevant to developing new annual Medicago spp. cultivars that offer improved disease resistance and better animal reproductive outcomes.

Separation of Chromatographic Co-Eluted Compounds by Clustering and by Functional Data Analysis

Peak overlapping is a common problem in chromatography, mainly in the case of complex biological mixtures, i.e., metabolites. Due to the existence of the phenomenon of co-elution of different compounds with similar chromatographic properties, peak separation becomes challenging. In this paper, two computational methods of separating peaks, applied, for the first time, to large chromatographic datasets, are described, compared, and experimentally validated. The methods lead from raw observations to data that can form inputs for statistical analysis. First, in both methods, data are normalized by the mass of sample, the baseline is removed, retention time alignment is conducted, and detection of peaks is performed. Then, in the first method, clustering is used to separate overlapping peaks, whereas in the second method, functional principal component analysis (FPCA) is applied for the same purpose. Simulated data and experimental results are used as examples to present both methods and to compare them. Real data were obtained in a study of metabolomic changes in barley (Hordeum vulgare) leaves under drought stress. The results suggest that both methods are suitable for separation of overlapping peaks, but the additional advantage of the FPCA is the possibility to assess the variability of individual compounds present within the same peaks of different chromatograms.

Transcriptome and metabolome profiling in naturally infested Casuarina equisetifolia clones by Ralstonia solanacearum

Casuarina equisetifolia is an important pioneer tree and suffers from bacterial wilt caused by Ralstonia solanacearum. We collected resistant (R) and susceptible (S) C. equisetifolia clones naturally infected by R. solanacearum and compared their transcriptome and metabolome with a clone (CK) from a non-infested forest, in order to study their response and resistance to bacterial wilt. We identified 18 flavonoids differentially accumulated among the three clonal groups as potential selection biomarkers against R. solanacearum. Flavonoid synthesis-related genes were up-regulated in the resistant clones, probably enhancing accumulation of flavonoids and boosting resistance against bacterial wilt. The down-regulation of auxin/indoleacetic acid-related genes and up-regulation of brassinosteroid, salicylic acid and jasmonic acid-related differentially expressed genes in the R vs CK and R vs S clonal groups may have triggered defense signals and increased expression of defense-related genes against R. solanacearum. Overall, this study provides an important insight into pathogen-response and resistance to bacterial wilt in C. equisetifolia.

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.

Dragon’s Blood from Dracaena cambodiana in China: Applied History and Induction Techniques toward Formation Mechanism

Dragon’s blood that is extracted from Dracaena plants has been widely used as traditional medicine in various ancient cultures. The application of dragon’s blood has a cherished history in China, even though the original plants were not discovered for some period. Dracaena cochinchinensis and Dracaena cambodiana were successively discovered in southern China during the 1970s–1980s. In the last half of the century, Chinese scientists have extensively investigated the production of dragon’s blood from these two Dracaena species, whereas these results have not been previously systematically summarized, as in the present paper. Herein, we present the applied history in ancient China and artificially induced technologies for dragon’s blood development based on these two Dracaena species, in particular, using tissue cultures seedlings and tender plants of D. cambodiana. Big data research, including transcriptomic and genomic studies, has suggested that dragon’s blood might be a defense substance that is secreted by Dracaena plants in response to (a)biotic stimuli. This review represents an effort to highlight the progress and achievements from applied history as well as induction techniques that are used for the formation of dragon’s blood that have taken place in China. Such knowledge might aid in the global conservation of wild Dracaena species and contribute to understanding dragon blood formation mechanisms, eventually assisting in the efficient utilization of limited Dracaena plant resources for the sustainable production of dragon’s blood.

Flavonoids with antibacterial and antioxidant potentials from the stem bark of Uapaca heudelotti

Two flavonol glycosides; U1: naringenin-7-O-glucoside and U2: kaempferol-3-O-glucoside were isolated for the first time, from ethyl acetate fraction of the stem bark of a traditional medicinal plant called Uapaca heudelotti. IR and NMR spectroscopy were used to elucidate the structures of the isolated compound. The two compounds were active against the 7 tested microorganisms; Escherichia coli, Bacillus subtilis, Salmonella typhi, Streptococcus pyogenes, Klebsiella pneumoniae, Staphylococcus aureus and Proteus mirabilis. The zones of inhibition of the compounds ranged from 16 to 23 mm. The MIC value was as low as 6.25 μg/mL against Salmonella typhi, Streptococcus pyogenes, and Bacillus subtilis. The radical scavenging activity of compound U1 and U2 was 80 and 85 % at 240 μg/mL, while that of the standard drug was 98% at 240 μg/mL. The results show an existent possibility of using the plant for the treatment of microbial diseases.

Extraction and Determination of Polar Bioactive Compounds from Alfalfa (Medicago sativa L.) Using Supercritical Techniques

The aim of this research was to select parameters for supercritical extraction with CO₂ of Medicago sativa L., considered as functional food, in quarter-technical plant, providing the highest concentration of bioactive polar constituents and simultaneously maintaining the highest efficiency of the process. For the purpose of optimization, mathematical statistics was used. Qualitative analysis of products was performed with supercritical fluid chromatography (SFC). The SFC analysis revealed a proper separation of flavonoids and phenolics acids for dedicated TFC and TPC optimal parameters. The obtained results have proved that it is a possibility to extract polar compounds with non-polar solvent under higher values of pressure and temperature and to enrich product with desired group of bioactive compounds with proper optimization. The proposed extraction technique allows to obtain on an industrial scale, using an environmentally friendly solvent, a preparation rich in biologically active nutrients that can be implemented in the cosmetics, pharmaceutical and food industries.

Metabolomics of Solanum lycopersicum Infected with Phytophthora infestans Leads to Early Detection of Late Blight in Asymptomatic Plants

Tomato crops suffer attacks of various pathogens that cause large production losses. Late blight caused by Phytophthora infestans is a devastating disease in tomatoes because of its difficultly to control. Here, we applied metabolomics based on liquid chromatography⁻mass spectrometry (LC-MS) and metabolic profiling by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) in combination with multivariate data analysis in the early detection of late blight on asymptomatic tomato plants and to discriminate infection times of 4, 12, 24, 36, 48, 60, 72 and 96 h after inoculation (hpi). MALDI-MS and LC-MS profiles of metabolites combined with multivariate data analysis are able to detect early-late blight-infected tomato plants, and metabolomics based on LC-MS discriminates infection times in asymptomatic plants. We found the metabolite tomatidine as an important biomarker of infection, saponins as early infection metabolite markers and isocoumarin as early and late asymptomatic infection marker along the post infection time. MALDI-MS and LC-MS analysis can therefore be used as a rapid and effective method for the early detection of late blight-infected tomato plants, offering a suitable tool to guide the correct management and application of sanitary defense approaches. LC-MS analysis also appears to be a suitable tool for identifying major metabolites of asymptomatic late blight-infected tomato plants.

Time-course metabolic profiling in alfalfa leaves under Phoma medicaginis infection

Information on disease process and pathogenicity mechanisms is important for understanding plant disease. Spring black stem and leaf spot caused by the necrotrophic pathogen Phoma medicaginis var. medicaginis Malbr. & Roum causes large losses to alfalfa. However, till now, little is known about alfalfa-P. medicagnis interactions and the pathogenicity mechanisms of the pathogen. Here, alfalfa inoculated with P. medicaginis was subjected to GC-MS based metabolic profiling. The metabolic response in P. medicaginis-inoculated and mock-inoculated alfalfa leaves was assessed at 2, 4, 6, 8, 12, 16, 20, 24, 26 and 28 days post inoculation. In total, 101 peaks were detected in the control and inoculated groups, from which 70 metabolites were tentatively identified. Using multivariate analysis, 16 significantly regulated compounds, including amino acids, nitrogen-containing compounds and organic acids, polyols, fatty acids, and sugars were tentatively identified (Variable importance values, VIP>1.0 and p <0.05). Among these metabolites, the levels of malate, 5-oxoproline, palmitic acid and stearic acid were increased significantly in P. medicaginis-infected alfalfa leaves compared to the controls. In contrast, the levels ofγ-aminobutyric acid and 2-pyrrolidinone were significantly decreased in infected leaves compared to the controls. Further metabolic pathway analysis of the 16 significantly regulated compounds demonstrated that glycolysis, the tricarboxylic acid cycle, and β-oxidation of fatty acids were significantly induced in the alfalfa leaves at later stages of P. medicaginis infection. The strong induction of tricarboxylic acid cycle pathways at later infection stages caused by the pathogen may induce senescence in the alfalfa leaves, leading to plant death. However, intermediate metabolites of these metabolic pathways, and inositol phosphate, glutathione, the metabolic pathways of some amino acids accumulated rapidly and strongly at early stages of infection, which may enhance the ability of alfalfa to resist necrotrophic P. medicaginis disease. Understanding metabolic pathways is essential for understanding pathogenesis.

Isoflavonoids as wound healing agents from Ononidis Radix

ETHNOPHARMACOLOGICAL RELEVANCE

Dried roots of Ononis spinosa L. are traditionally used for their diuretic, anti-inflammatory and wound healing effects.

AIM OF THE STUDY

Isolation of the bioactive compounds of Ononis spinosa L. subsp. leiosperma (Boiss.) Sirj.

MATERIALS AND METHODS

Ethyl acetate extract prepared from the roots of Ononis spinosa L. subsp. leiosperma (Boiss.) Sirj. was subjected to silica gel column. The fractions were tested for their wound healing and anti-inflammatory activities. Linear incision and circular excision wound models and hydroxypyroline estimation assay were used for the wound healing activity. Carrageenan-induced hind paw edema, TPA-induced ear edema and acetic acid-induced increase in capillary permeability tests as acute inflammation; FCA-induced arthritis as chronic inflammation models were used for the assessment of anti-inflammatory activity. Antioxidant capacities of the fractions were tested using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, 2,2-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid (ABTS) scavenging activity assay, reducing power assay and hydroxyl radical (OH^-) scavenging assay. The isolation procedure was continued with the active fraction (Fr-E5).

RESULTS

Fr-E5 exhibited remarkable wound healing activity with the 33.4% tensile strength value on the linear incision wound model and 51.4% reduction of the wound area at the day 12 on the circular excision wound model. Hydroxyproline content of the tissue treated by Fr-E5 was found to be 30.9 ± 0.72μg/mg. Acetic acid induced increase in capillary permeability test results revealed that Fr-E5 inhibited inflammation by the value of 40.3%. Fr-E5 showed 28.1-32.2% inhibition in carrageenan-induced hind paw edema test while did not possess activity on TPA-induced ear edema and FCA-induced arthritis models. Trifolirhizin, ononin, medicarpin-3-O-glucoside, onogenin-7-O-glucoside and sativanone-7-O-glucoside were isolated from Fr-E5 and tested for their wound healing activities using by measuring their inhibition of hyaluronidase, collagenase and elastase enzymes. Ononin and sativanone-7-O-glucoside inhibited hyaluronidase and elastase enzymes by 31.66% and 41.75%; 45.58% and 46.88% values respectively at the dose of 100μg/mL.

CONCLUSION

Among five isolated compounds, ononin and sativanone-7-O-glucoside were found to inhibit hyaluronidase and elastase enzymes. According to the results, these compounds may majorly be responsible for the wound healing activity of the extract.

Isolation and Characterization of Key Genes that Promote Flavonoid Accumulation in Purple-leaf Tea (Camellia sinensis L.)

There were several high concentrations of flavonoid components in tea leaves that present health benefits. A novel purple-leaf tea variety, 'Mooma1', was obtained from the natural hybrid population of Longjing 43 variety. The buds and young leaves of 'Mooma1' were displayed in bright red. HPLC and LC-MS analysis showed that anthocyanins and O-Glycosylated flavonols were remarkably accumulated in the leaves of 'Mooma1', while the total amount of catechins in purple-leaf leaves was slightly decreased compared with the control. A R2R3-MYB transcription factor (CsMYB6A) and a novel UGT gene (CsUGT72AM1), that were highly expressed in purple leaf were isolated and identified by transcriptome sequencing. The over-expression of transgenic tobacco confirmed that CsMYB6A can activate the expression of flavonoid-related structural genes, especially CHS and 3GT, controlling the accumulation of anthocyanins in the leaf of transgenic tobacco. Enzymatic assays in vitro confirmed that CsUGT72AM1 has catalytic activity as a flavonol 3-O-glucosyltransferase, and displayed broad substrate specificity. The results were useful for further elucidating the molecular mechanisms of the flavonoid metabolic fluxes in the tea plant.

Functional Genomics in the Study of Metabolic Pathways in Medicago truncatula: An Overview

In addition to its value as a model system for studies on symbiotic nitrogen fixation, Medicago truncatula has recently become an organism of choice for dissection of complex pathways of secondary metabolism. This work has been driven by two main reasons, both with practical implications. First Medicago species possess a wide range of flavonoid and terpenoid natural products, many of which, for example, the isoflavonoids and triterpene saponins, have important biological activities impacting both plant and animal (including human) health. Second, M. truncatula serves as an excellent model for alfalfa, the world's major forage legume, and forage quality is determined in large part by the concentrations of products of secondary metabolism, particularly lignin and condensed tannins. We here review recent progress in understanding the pathways leading to flavonoids, lignin, and triterpene saponins through utilization of genetic resources in M. truncatula.

Ethylene Signaling Is Important for Isoflavonoid-Mediated Resistance to Rhizoctonia solani in Roots of Medicago truncatula

The root-infecting necrotrophic fungal pathogen Rhizoctoniasolani causes significant disease to all the world's major food crops. As a model for pathogenesis of legumes, we have examined the interaction of R. solani AG8 with Medicago truncatula. RNAseq analysis of the moderately resistant M. truncatula accession A17 and highly susceptible sickle (skl) mutant (defective in ethylene sensing) identified major early transcriptional reprogramming in A17. Responses specific to A17 included components of ethylene signaling, reactive oxygen species metabolism, and consistent upregulation of the isoflavonoid biosynthesis pathway. Mass spectrometry revealed accumulation of the isoflavonoid-related compounds liquiritigenin, formononetin, medicarpin, and biochanin A in A17. Overexpression of an isoflavone synthase in M. truncatula roots increased isoflavonoid accumulation and resistance to R. solani. Addition of exogenous medicarpin suggested this phytoalexin may be one of several isoflavonoids required to contribute to resistance to R. solani. Together, these results provide evidence for the role of ethylene-mediated accumulation of isoflavonoids during defense against root pathogens in legumes. The involvement of ethylene signaling and isoflavonoids in the regulation of both symbiont-legume and pathogen-legume interactions in the same tissue may suggest tight regulation of these responses are required in the root tissue.

Cloning and expression analysis of chalcone synthase gene from Coleus forskohlii

Flavonoids are an important class of secondary metabolites that play various roles in plants such as mediating defense, floral pigmentation and plant-microbe interaction. Flavonoids are also known to possess antioxidant and antimicrobial activities. Coleus forskohlii (Willd.) Briq. (Lamiaceae) is an important medicinal herb with a diverse metabolic profile, including production of a flavonoid, genkwanin. However, components of the flavonoid pathway have not yet been studied in this plant. Chalcone synthase (CHS) catalyses the first committed step of flavonoid biosynthetic pathway. Full-length cDNA, showing homology with plant CHS gene was isolated from leaves of C. forskohlii and named CfCHS (GenBank accession no. KF643243). Theoretical translation of CfCHS nucleotide sequence shows that it encodes a protein of 391 amino acids with a molecular weight of 42.75 kDa and pI 6.57. Expression analysis of CfCHS in different tissues and elicitor treatments showed that methyl jasmonate (MeJA) strongly induced its expression. Total flavonoids content and antioxidant activity of C. forskohlii also got enhanced in response to MeJA, which correlated with increased CfCHS expression. Induction of CfCHS by MeJA suggest its involvement in production of flavonoids, providing protection from microbes during herbivory or mechanical wounding. Further, our in silico predictions and experimental data suggested that CfCHS may be posttranscriptionally regulated by miR34.

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.

Gene Expression Changes during the Gummosis Development of Peach Shoots in Response to Lasiodiplodia theobromae Infection Using RNA-Seq

Lasiodiplodia theobromae is a causal agent of peach (Prunus persica L.) tree gummosis, a serious disease affecting peach cultivation and production. However, the molecular mechanism underlying the pathogenesis remains unclear. RNA-Seq was performed to investigate gene expression in peach shoots inoculated or mock-inoculated with L. theobromae. A total of 20772 genes were detected in eight samples; 4231, 3750, 3453, and 3612 differentially expressed genes were identified at 12, 24, 48, and 60 h after inoculation, respectively. Furthermore, 920 differentially co-expressed genes (515 upregulated and 405 downregulated) were found, respectively. Gene ontology annotation revealed that phenylpropanoid biosynthesis and metabolism, uridine diphosphate-glucosyltransferase activity, and photosynthesis were the most differentially regulated processes during gummosis development. Significant differences were also found in the expression of genes involved in glycometabolism and in ethylene and jasmonic acid biosynthesis and signaling. These data illustrate the dynamic changes in gene expression in the inoculated peach shoots at the transcriptome level. Overall, gene expression in defense response and glycometabolism might result in the gummosis of peach trees induced by L. theobromae.

BTH and BABA induce resistance in pea against rust (Uromyces pisi) involving differential phytoalexin accumulation

MAIN CONCLUSION

Systemic acquired resistance elicitors, BTH and BABA, reduce rust penetration in pea through phytoalexins pathway but differing in their mode of action. It has been previously shown that rust (Uromyces pisi) infection can be reduced in pea (Pisum sativum) by exogenous applications of systemic acquired resistance elicitors such as BTH and BABA. This protection is known to be related with the induction of the phenolic pathway but the particular metabolites involved have not been determined yet. In this work, we tackled the changes induced in phytoalexin content by BTH and BABA treatments in the context of the resistance responses to pea rust. Detailed analysis through high-performance liquid chromatography (HPLC) showed qualitative and quantitative differences in the content, as well as in the distribution of phytoalexins. Thus, following BTH treatment, we observed an increase in scopoletin, pisatin and medicarpin contents in all, excreted, soluble and cell wall-bound fraction. This suggests fungal growth impairment by both direct toxic effect as well as plant cell wall reinforcement. The response mediated by BTH was genotype-dependent, since coumarin accumulation was observed only in the resistant genotype whereas treatment by BABA primed phytoalexin accumulation in both genotypes equally. Exogenous application to the leaves of scopoletin, medicarpin and pisatin lead to a reduction of the different fungal growth stages, confirming a role for these phytoalexins in BTH- and BABA-induced resistance against U. pisi hampering pre- and postpenetration fungal stages.

Priming maize resistance by its neighbors: activating 1,4-benzoxazine-3-ones synthesis and defense gene expression to alleviate leaf disease

Plant disease can be effectively suppressed in intercropping systems. Our previous study demonstrated that neighboring maize plants can restrict the spread of soil-borne pathogens of pepper plants by secreting defense compounds into the soil. However, whether maize plant can receive benefits from its neighboring pepper plants in an intercropping system is little attention. We examined the effects of maize roots treated with elicitors from the pepper pathogen Phytophthora capsici and pepper root exudates on the synthesis of 1,4-benzoxazine-3-ones (BXs), the expression of defense-related genes in maize, and their ability to alleviate the severity of southern corn leaf blight (SCLB) caused by Bipolaris maydis. We found that SCLB was significantly reduced after the above treatments. The contents of 1,4-benzoxazine-3-ones (BXs: DIBOA, DIMBOA, and MBOA) and the expression levels of BX synthesis and defense genes in maize roots and shoots were up-regulated. DIMBOA and MBOA effectively inhibited the mycelium growth of Bipolaris maydis at physiological concentrations in maize shoots. Further studies suggested that the defense related pathways or genes in maize roots and shoots were activated by elicitors from the P. capsici or pepper root exudates. In conclusion, maize increased the levels of BXs and defense gene expression both in roots and shoots after being triggered by root exudates and pathogen from neighboring pepper plants, eventually enhancing its resistance.

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.

Structural analysis and profiling of phenolic secondary metabolites of Mexican lupine species using LC-MS techniques

Flavonoid glycoconjugates from roots and leaves of eight North America lupine species (Lupinus elegans, Lupinus exaltatus, Lupinus hintonii, Lupinus mexicanus, Lupinus montanus, Lupinus rotundiflorus, Lupinus stipulatus, Lupinus sp.), three Mediterranean species (Lupinus albus, Lupinus angustifolius, Lupinus luteus) and one species from South America domesticated in Europe (Lupinus mutabilis) were analyzed using two LC/MS systems: low-resolution ion trap instrument and high-resolution quadrupole-time-of-flight spectrometer. As a result of the LC/MS profiling using the CID/MS(n) experiments structures of 175 flavonoid glycoconjugates found in 12 lupine species were identified at three confidence levels according to the Metabolomic Standard Initiative, mainly at level 2 and 3, some of them were classified to the level 1. Among the flavonoid derivatives recognized in the plant extracts were isomeric or isobaric compounds, differing in the degree of hydroxylation of the aglycones and the presence of glycosidic, acyl or alkyl groups in the molecules. The elemental composition of the glycoconjugate molecules was established from the exact m/z values of the protonated/deprotonated molecules ([M+H](+)/[M-H](-)) measured with the accuracy better than 5 ppm. Information concerning structures of the aglycones, the type of sugar moieties (hexose, deoxyhexose or pentose) and, in some cases, their placement on the aglycones as well as the acyl substituents of the flavonoid glycoconjugates was achieved in experiments, in which collision-induced dissociation was applied. Flavonoid aglycones present in the studied O-glycoconjugates were unambiguously identified after the comparison of the pseudo-MS(3) spectra with the spectra registered for the standards. Isomers of flavonoid glycoconjugates, in which one or two sugar moieties were attached to 4'- or 7-hydroxyl groups or directly to the C-6 or C-8 of the aglycones, could be distinguished on the basis of the MS(2) spectra. However, the collision energy applied in the CID experiments had to be optimized for each group of the compounds and there were no universal settings that allowed the acquisition of structural information for all the compounds present in the sample. Information obtained from the flavonoid conjugate profiling was used for the chemotaxonomic comparison of the studied lupine species. A clear-cut discrimination of the Mediterranean and North American lupines was obtained as a result of this analysis.

Changes of phenolic secondary metabolite profiles in the reaction of narrow leaf lupin (Lupinus angustifolius) plants to infections with Colletotrichum lupini fungus or treatment with its toxin

Plant interactions with environmental factors cause changes in the metabolism and regulation of biochemical and physiological processes. Plant defense against pathogenic microorganisms depends on an innate immunity system that is activated as a result of infection. There are two mechanisms of triggering this system: basal immunity activated as a result of a perception of microbe-associated molecular patterns through pattern recognition receptors situated on the cell surface and effector-triggered immunity (ETI). An induced biosynthesis of bioactive secondary metabolites, in particular phytoalexins, is one of the mechanisms of plant defense to fungal infection. Results of the study on narrow leaf lupin (Lupinus angustifolius L.) plants infected with the anthracnose fungus Colletotrichum lupini and treated with fungal phytotoxic metabolites are described in the paper. The C. lupini phytotoxins were isolated from liquid cultures, purified and partially characterized with physicochemical methods. Accumulation of secondary metabolites on leaf surface and within the tissues of plants either infected, treated with the fungal phytotoxin or submitted to both treatments was studied using GC-MS and LC-MS, respectively. Substantial differences in isoflavone aglycones and glycoconjugate profiles occurred in response to different ways of plant treatment.

Genes of phenylpropanoid pathway are activated in early response to Fusarium attack in flax plants

Fusarium is the most common flax pathogen causing serious plant diseases and in most cases leading to plant death. To protect itself, the plant activates a number of genes and metabolic pathways, both to counteract the effects of the pathogen, and to eliminate the threat. The identification of the plant genes which respond to infection is the approach, that has been used in this study. Forty-seven flax genes have been identified by means of cDNA subtraction method as those, which respond to pathogen infection. Subtracted genes were classified into several classes and the prevalence of the genes involved in the broad spectrum of antioxidants biosynthesis has been noticed. By means of semi-quantitative RT-PCR and metabolite profiling, the involvement of subtracted genes controlling phenylpropanoid pathway in flax upon infection was positively verified. We identified the key genes of the synthesis of these compounds. At the same time we determined the level of the metabolites produced in the phenylpropanoid pathway (flavonoids, phenolic acids) in early response to Fusarium attack by means of GC-MS technique. To the best of our knowledge this is the first report to describe genes and metabolites of early flax response to pathogens studied in a comprehensive way.

Phytoalexins in defense against pathogens

Plants use an intricate defense system against pests and pathogens, including the production of low molecular mass secondary metabolites with antimicrobial activity, which are synthesized de novo after stress and are collectively known as phytoalexins. In this review, we focus on the biosynthesis and regulation of camalexin, and its role in plant defense. In addition, we detail some of the phytoalexins produced by a range of crop plants from Brassicaceae, Fabaceae, Solanaceae, Vitaceae and Poaceae. This includes the very recently identified kauralexins and zealexins produced by maize, and the biosynthesis and regulation of phytoalexins produced by rice. Molecular approaches are helping to unravel some of the mechanisms and reveal the complexity of these bioactive compounds, including phytoalexin action and metabolism.

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

Hairy roots and suspension cell cultures are commonly used in deciphering different problems related to the biochemistry and physiology of plant secondary metabolites. Here, we address about the issue of possible differences in the profiles of flavonoid compounds and their glycoconjugates derived from various plant materials grown in a standard culture media. We compared profiles of flavonoids isolated from seedling roots, hairy roots, and suspension root cell cultures of a model legume plant, Medicago truncatula. The analyses were conducted with plant isolates as well as the media. The LC/MS profiles of target natural products obtained from M. truncatula seedling roots, hairy roots, and suspension root cell cultures differed substantially. The most abundant compounds in seedlings roots were mono- and diglucuronides of isoflavones and/or flavones. This type of glycosylation was not observed in hairy roots or suspension root cell cultures. The only recognized glycoconjugates in the latter samples were glucose derivatives of isoflavones. Application of a high-resolution mass spectrometer helped evaluate the elemental composition of protonated molecules, such as [M + H](+). Comparison of collision-induced dissociation MS/MS spectra registered with a quadrupole time-of-flight analyzer for tissue extracts and standards allowed us to estimate the aglycone structure on the basis of the pseudo-MS(3) experiment. Structures of these natural products were described according to the registered mass spectra and literature data. The analyses conducted represent an overview of flavonoids and their conjugates in different types of plant material representing the model legume, M. truncatula. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11306-011-0287-2) contains supplementary material, which is available to authorized users.

Expression of coordinately regulated defence response genes and analysis of their role in disease resistance in Medicago truncatula

Microarray technology was used to identify the genes associated with disease defence responses in the model legume Medicago truncatula. Transcript profiles from M. truncatula cv. Jemalong genotype A17 leaves inoculated with Colletotrichum trifolii and Erysiphe pisi and roots infected with Phytophthora medicaginis were compared to identify the genes expressed in response to all three pathogens and genes unique to an interaction. The A17 genotype is resistant to C. trifolii and E. pisi, exhibiting a hypersensitive response after inoculation, and is moderately susceptible to P. medicaginis. Among the most strongly up-regulated genes in all three interactions were those encoding a hevein-like protein, thaumatin-like protein (TLP) and members of the pathogenesis response (PR)10 family. Transcripts of genes for enzymes in the phenylpropanoid pathway leading to the production of isoflavonoid phytoalexins increased dramatically in response to inoculation with the foliar pathogens. In P. medicaginis-inoculated roots, transcripts of genes in the phenylpropanoid pathway peaked at 5 days post-inoculation, when symptoms became visible. Transcript accumulation of three PR10 family members, a TLP and chalcone synthase (CHS) was assessed in M. truncatula genotype R108 plants. The R108 plants are resistant to C. trifolii and moderately susceptible to E. pisi and P. medicaginis. Transcript accumulation paralleled the stages of pathogen development. To evaluate the role of a TLP, a PR10 family member and CHS in disease resistance, transgenic R108 plants containing interfering RNA (RNAi) constructs were produced. Reduced expression of PR10 and TLP had no effect on the disease phenotype, whereas reduced expression of CHS resulted in increased susceptibility to necrotrophic pathogens.

In-source fragmentation and accurate mass analysis of multiclass flavonoid conjugates by electrospray ionization time-of-flight mass spectrometry

In-source collision-induced dissociation (CID) fragmentation features of multiclass flavonoid glycoconjugates were examined using liquid chromatography electrospray time-of-flight mass spectrometry. Systematic experiments were performed to search for optimal conditions for in-source fragmentation in both positive and negative ion modes. The objective of the study was to attain uniformly appropriate conditions for a wide range of analytes independently of the aglycone, the attached sugar part and the type of bond between the aglycone and the glycan moieties (O- or C-glycosides). Studied substances included representatives of flavonols, flavones, flavanones and anthocyanins and, regarding their glycan parts, mono-, di- and triglycosides with varying distribution of carbohydrate moieties (di-O-glycosides, O-diglycosides, O,C-diglycosides). The breakdown properties of the analytes along with the abundances of the characteristic diagnostic ions required for structural elucidation of complex flavonoid derivatives were evaluated. An optimized value was found for the instrument parameter (fragmentor voltage) affecting the in-source CID fragmentation of the analytes [230 V (ESI+) and 330 V (ESI-)]. Thus, appropriate performance in terms of both highly sensitive full-scan acquisition and fragmentation information was obtained for all the investigated flavonoids. In addition, singularities in the abundance of selected diagnostic ions (e.g. Y(0), Y(1) and Y*) due to variations in the interglycosidic linkage (rutinoside-neohesperidoside) in the glycan part were found and are also evaluated and discussed in detail. The combination of in-source CID fragmentation with high mass accuracy MS detection establishes a working basis for the development of versatile and useful LC-MS methods for wide-scope screening, non-targeted detection and tentative identification of flavonoid derivatives.