Modulation of phenolic metabolism under stress conditions in a Lotus japonicus mutant lacking plastidic glutamine synthetase

Mutation of MYB36 affects isoflavonoid metabolism, growth, and stress responses in Lotus japonicus

Isoflavonoids are mostly produced by legumes although little is known about why and how legumes are able to regulate the biosynthesis of these particular compounds. Understanding the role of potential regulatory genes of the isoflavonoid biosynthetic pathway constitutes an important topic of research. The LORE1 mutation of the gene encoding the transcription factor MYB36 allowed the identification of this gene as a regulator of isoflavonoid biosynthesis in Lotus japonicus plants. The levels of several isoflavonoid compounds were considerably lower in two lines of Ljmyb36 mutant plants compared to the WT. In addition, we found that Ljmyb36 mutant plants were significantly smaller and showed a substantial decrease in the chlorophyll levels under normal growth conditions. The analysis of plants subjected to different types of abiotic stress conditions further revealed that mutant plants presented a higher sensitivity than WT plants, indicating that the MYB36 transcription factor is also involved in the stress response in L. japonicus plants.

Photorespiration: regulation and new insights on the potential role of persulfidation

Photorespiration has been considered a 'futile' cycle in C3 plants, necessary to detoxify and recycle the metabolites generated by the oxygenating activity of Rubisco. However, several reports indicate that this metabolic route plays a fundamental role in plant metabolism and constitutes a very interesting research topic. Many open questions still remain with regard to photorespiration. One of these questions is how the photorespiratory process is regulated in plants and what factors contribute to this regulation. In this review, we summarize recent advances in the regulation of the photorespiratory pathway with a special focus on the transcriptional and post-translational regulation of photorespiration and the interconnections of this process with nitrogen and sulfur metabolism. Recent findings on sulfide signaling and protein persulfidation are also described.

Primary and Secondary Metabolites in Lotus japonicus

Lotus japonicus is a leguminous model plant used to gain insight into plant physiology, stress response, and especially symbiotic plant-microbe interactions, such as root nodule symbiosis or arbuscular mycorrhiza. Responses to changing environmental conditions, stress, microbes, or insect pests are generally accompanied by changes in primary and secondary metabolism to account for physiological needs or to produce defensive or signaling compounds. Here we provide an overview of the primary and secondary metabolites identified in L. japonicus to date. Identification of the metabolites is mainly based on mass spectral tags (MSTs) obtained by gas chromatography linked with tandem mass spectrometry (GC-MS/MS) or liquid chromatography-MS/MS (LC-MS/MS). These MSTs contain retention index and mass spectral information, which are compared to databases with MSTs of authentic standards. More than 600 metabolites are grouped into compound classes such as polyphenols, carbohydrates, organic acids and phosphates, lipids, amino acids, nitrogenous compounds, phytohormones, and additional defense compounds. Their physiological effects are briefly discussed, and the detection methods are explained. This review of the exisiting literature on L. japonicus metabolites provides a valuable basis for future metabolomics studies.

The fate of secondary metabolites in plants growing on Cd-, As-, and Pb-contaminated soils-a comprehensive review

The study used scattered literature to summarize the effects of excess Cd, As, and Pb from contaminated soils on plant secondary metabolites/bioactive compounds (non-nutrient organic substances). Hence, we provided a systematic overview involving the sources and forms of Cd, As, and Pb in soils, plant uptake, mechanisms governing the interaction of these risk elements during the formation of secondary metabolites, and subsequent effects. The biogeochemical characteristics of soils are directly responsible for the mobility and bioavailability of risk elements, which include pH, redox potential, dissolved organic carbon, clay content, Fe/Mn/Al oxides, and microbial transformations. The radial risk element flow in plant systems is restricted by the apoplastic barrier (e.g., Casparian strip) and chelation (phytochelatins and vacuole sequestration) in roots. However, bioaccumulation is primarily a function of risk element concentration and plant genotype. The translocation of risk elements to the shoot via the xylem and phloem is well-mediated by transporter proteins. Besides the dysfunction of growth, photosynthesis, and respiration, excess Cd, As, and Pb in plants trigger the production of secondary metabolites with antioxidant properties to counteract the toxic effects. Eventually, this affects the quantity and quality of secondary metabolites (including phenolics, flavonoids, and terpenes) and adversely influences their antioxidant, antiinflammatory, antidiabetic, anticoagulant, and lipid-lowering properties. The mechanisms governing the translocation of Cd, As, and Pb are vital for regulating risk element accumulation in plants and subsequent effects on secondary metabolites.

Role of Promising Secondary Metabolites to Confer Resistance Against Environmental Stresses in Crop Plants: Current Scenario and Future Perspectives

Plants often face incompatible growing environments like drought, salinity, cold, frost, and elevated temperatures that affect plant growth and development leading to low yield and, in worse circumstances, plant death. The arsenal of versatile compounds for plant consumption and structure is called metabolites, which allows them to develop strategies to stop enemies, fight pathogens, replace their competitors and go beyond environmental restraints. These elements are formed under particular abiotic stresses like flooding, heat, drought, cold, etc., and biotic stress such as a pathogenic attack, thus associated with survival strategy of plants. Stress responses of plants are vigorous and include multifaceted crosstalk between different levels of regulation, including regulation of metabolism and expression of genes for morphological and physiological adaptation. To date, many of these compounds and their biosynthetic pathways have been found in the plant kingdom. Metabolites like amino acids, phenolics, hormones, polyamines, compatible solutes, antioxidants, pathogen related proteins (PR proteins), etc. are crucial for growth, stress tolerance, and plant defense. This review focuses on promising metabolites involved in stress tolerance under severe conditions and events signaling the mediation of stress-induced metabolic changes are presented.

Differential Expression of Calycosin-7-O-β-D-glucoside Biosynthesis Genes and Accumulation of Related Metabolites in Different Organs of Astragalus membranaceus Bge. var. mongholicus (Bge.) Hsiao Under Drought Stress

Calycosin-7-O-β-D-glycoside (CG), as a flavonoid, plays an important role in the abiotic stress response of Astragalus membranaceus Bge. var. mongholicus (Bge.) Hsiao (A. mongholicus). CG is also an active ingredient in A. mongholicus with high medicinal value. However, the response mechanism of the CG biosynthetic pathway of drought stress is not clear. In this research, drought stress was inflicted upon A. mongholicus, and the variations in flavonoid metabolites and the correlating gene expression in CG biosynthesis were studied in roots, stems, and leaves of A. mongholicus by UHPLC-MRM-MS/MS and qRT-PCR. Drought stress reduced the dry weight and increased the content of malondialdehyde (MDA) and proline. Drought was beneficial to the accumulation of L-phenylalanine and 4-coumaric acid in leaves and promoted the accumulation of all target compounds in the roots, except calycosin. Overexpression of AmIOMT was observed in the leaves, but the content of formononetin which is the product of isoflavone O-methyltransferase (IOMT) catalysis was higher in stems than in leaves. This research aims to further understand the acclimation of abiotic stress and the regulation mechanism of flavonoid accumulation in A. mongholicus.

Special Issue Editorial: Plant Nitrogen Assimilation and Metabolism

Nitrogen is an important macronutrient for plant growth and development. Research has long been carried out to elucidate the mechanisms involved in nitrogen uptake, assimilation, and utilization in plants. However, despite recent advances, many of these mechanisms still are not fully understood. In this special issue, several research articles and two reviews, all of them aiming to elucidate some specific aspects of nitrogen (N) metabolism, are presented. Together, the articles in this issue provide a state-of-the-art perspective on important questions related to nitrogen metabolism in photosynthetic organisms, highlighting the fundamental importance of research in this field.

Cell wall response to UV radiation in needles of Picea omorika

The UV-B represents the minor fraction of the solar spectrum, while UV-C is not contained in natural solar radiation, but both radiation types can cause damaging effects in plants. Cell walls (CWs) are one of the targets for external stressors. Juvenile P. omorika trees were treated either with 21 day-high doses UV-B or with 7 day- UV-C in open-top chambers. Using spectroscopic and biochemical techniques, it was shown that the response to UV radiation includes numerous modifications in needle CW structure: relative content of xylan, xyloglucan, lignin and cellulose decreased; cellulose crystallinity changed; yield of lignin monomers with stronger connection of CC in side chain with the ring increased; re-distribution of inter- and intra-polymer H-bonds occurred. The recovery was mediated by an increase in the activities and changes in isoform profiles of CW bound covalent peroxidases (POD) and polyphenol oxidases (PO) (UV-B), and ionic POD and covalent PO (UV-C). A connection between activities of specific POD/PO isoforms and phenolic species (m- and p-coumaric acid, pinoresinol and cinnamic acid derivatives) was demonstrated, and supported by changes in the sRNA profile. In vivo fluorometry showed phenolics accumulation in needle epidermal CWs. These results imply transversal connections between polymers and changed mechanical properties of needle CW as a response to UV. The CW alterations enabled maintenance of physiological functions, as indicated by the preserved chlorophyll content and/or organization. The current study provides evidence that in conifers, needle CW response to both UV-B and UV-C includes biochemical modifications and structural remodeling.

Isolation and characterization of chloroplastic glutamine synthetase gene (CsGS2) in tea plant Camellia sinensis

Tea plant (Camellia sinensis) is an ammonium preferring plant species. However, little is known about the mechanism underlying this preference. Herein, a chloroplastic glutamine synthetase gene (CsGS2), which is vital for nitrogen assimilation in mesophyll tissue, was isolated from tea cultivar C. sinensis cv. 'Longjing43'. The full length cDNA of CsGS2 was 1622 bp, having a 1299 bp open reading frame encoding a 432-amino acid protein. Homology search and sequence analysis demonstrated that CsGS2 protein carried the basic characteristics of a canonical GS2 domain and shared high identity with GS2s from other plant species. Subcellular localization and immunolocalization of CsGS2 revealed that it is localized in chloroplast. qRT-PCR and Western blot analyses showed that CsGS2 was expressed in a leaf-specific pattern, such that both CsGS2 and its protein were most abundant in mature leaves. Temporal expression patterns of CsGS2 showed minor differences in response to ammonium and nitrate nutrition. The transcript level of CsGS2 was significantly induced in mature leaves during the development of new shoots, whereas darkness inhibited this induction significantly. These results suggested that CsGS2 does not play a role in the differential utilization mechanisms of differing nitrogen forms in tea, and imply a light dependent transcription regulation in mature leaves during the development of new shoots.

Comparison of Different Extraction Methods for the Phenolic Compounds Recovery with the Antioxidant Activity of Bougainvillea x buttiana

Background:

Bougainvillea x buttiana has long been used as a Mexican conventional medicinal drug to cure different sicknesses.

Objective:

In this work, the consequences of ethanol combination and temperature extraction for phenolic compound recovery with the biological activity in Bougainvillea x buttiana extracts were investigated.

Materials and Methods:

The phenolic recovery from Bougainvillea x buttiana was determined by comparing the effects of ethanol 0%, 50-100% (v/v) and extraction temperature (26, 45 and 64°C). The total phenolic content was investigated using spectrophotometric methods. Antioxidant activity from different Bougainvillea x buttiana extracts was evaluated by determining their potential to scavenge the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical. The chemical compositions and cytotoxic effect of extracts were determined using GC-MS techniques and the crystal violet technique, respectively.

Results:

Our results confirmed that all extractions with different concentrations and temperatures had significant effects over the total phenolic contents and antioxidant activity (DPPH) of the extracts. The best recuperation of the total phenol content was observed in extracts with 60% ethanol at 26°C (201.08 mgEGA/g dry extract). Extracts with 100% ethanol at 26°C showed the highest antioxidant activity (IC50 was 286.75 μg/mL). GC-MS revealed the presence of various phytochemical contents with polar and non-polar properties. The phenolic compounds were investigated as to the structure, quantity and position of the hydroxyl groups on the benzene ring.

Conclusion:

The ethanolic extract of Bougainvillea x buttiana was confirmed to have high phenolic content and contain pharmacologically active compounds, with potent antioxidant effects and low cytotoxic effects.

Flavonoids and Isoflavonoids Biosynthesis in the Model Legume Lotus japonicus; Connections to Nitrogen Metabolism and Photorespiration

Phenylpropanoid metabolism represents an important metabolic pathway from which originates a wide number of secondary metabolites derived from phenylalanine or tyrosine, such as flavonoids and isoflavonoids, crucial molecules in plants implicated in a large number of biological processes. Therefore, various types of interconnection exist between different aspects of nitrogen metabolism and the biosynthesis of these compounds. For legumes, flavonoids and isoflavonoids are postulated to play pivotal roles in adaptation to their biological environments, both as defensive compounds (phytoalexins) and as chemical signals in symbiotic nitrogen fixation with rhizobia. In this paper, we summarize the recent progress made in the characterization of flavonoid and isoflavonoid biosynthetic pathways in the model legume Lotus japonicus (Regel) Larsen under different abiotic stress situations, such as drought, the impairment of photorespiration and UV-B irradiation. Emphasis is placed on results obtained using photorespiratory mutants deficient in glutamine synthetase. The results provide different types of evidence showing that an enhancement of isoflavonoid compared to standard flavonol metabolism frequently occurs in Lotus under abiotic stress conditions. The advance produced in the analysis of isoflavonoid regulatory proteins by the use of co-expression networks, particularly MYB transcription factors, is also described. The results obtained in Lotus japonicus plants can be also extrapolated to other cultivated legume species, such as soybean, of extraordinary agronomic importance with a high impact in feeding, oil production and human health.

Arabidopsis thaliana mutants devoid of chloroplast glutamine synthetase (GS2) have non-lethal phenotype under photorespiratory conditions

Chloroplast located Glutamine Synthetase (GS2) is believed to play a major role in the reassimilation of ammonium generated by photorespiration, being GS2 knockout mutants unable to grow under photorespiratory conditions (low-CO₂ atmosphere) in the species characterized so far (Barley, Lotus). To investigate the importance of GS2 in A. thaliana nitrogen metabolism mutant plants devoid of this GS isoenzyme were characterized. It was shown that GS2 mutants although smaller, slightly chlorotic and with the nitrogen metabolism impaired, were able to grow and complete their life cycle under ordinary air conditions. Surprisingly, GS2 mutants were more tolerant to salt stress than wild-type plants. The lack of GS2 seems to be compensated by higher expression of some GS cytosolic isogenes, namely GLN1;2 and GLN1;3 and by glutamate dehydrogenase, whose activity and expression is enhanced in the GS2 mutant plants and might account for the increased tolerance to salt stress. Under conditions that minimize photorespiration (CO2-enriched atmosphere) plant growth and ammonium assimilation impairment is less evident in the GS2 mutant plants and is accompanied by an adjustment of levels of expression of the cytosolic isogenes, with an increase in the expression of GLN1;3 and a decrease in the expression of the GLN1;1 and GLN1;2. Altogether the results confirm a major role of GS2 in the assimilation of ammonium released during photorespiration, but suggest a redundancy of activity with cytosolic GSs and GDH and further support the involvement of the chloroplastic isoenzyme in primary nitrogen assimilation and plant growth and development in A. thaliana.

Response of Phenylpropanoid Pathway and the Role of Polyphenols in Plants under Abiotic Stress

Phenolic compounds are an important class of plant secondary metabolites which play crucial physiological roles throughout the plant life cycle. Phenolics are produced under optimal and suboptimal conditions in plants and play key roles in developmental processes like cell division, hormonal regulation, photosynthetic activity, nutrient mineralization, and reproduction. Plants exhibit increased synthesis of polyphenols such as phenolic acids and flavonoids under abiotic stress conditions, which help the plant to cope with environmental constraints. Phenylpropanoid biosynthetic pathway is activated under abiotic stress conditions (drought, heavy metal, salinity, high/low temperature, and ultraviolet radiations) resulting in accumulation of various phenolic compounds which, among other roles, have the potential to scavenge harmful reactive oxygen species. Deepening the research focuses on the phenolic responses to abiotic stress is of great interest for the scientific community. In the present article, we discuss the biochemical and molecular mechanisms related to the activation of phenylpropanoid metabolism and we describe phenolic-mediated stress tolerance in plants. An attempt has been made to provide updated and brand-new information about the response of phenolics under a challenging environment.

Induction of isoflavonoid biosynthesis in Lotus japonicus after UV-B irradiation

Enhanced ultraviolet radiation (UV) is an important environmental factor that may cause reductions in the growth and productivity of plants. In the present work we studied the response to UV-B radiation in leaves of the model legume Lotus japonicus. After UV-B treatment, induction of phenyalanine-ammonia lyase gene expression and enzyme activity was detected. Among the ten genes encoding for PAL found in the L. japonicus genome, LjPAL1 was both the most expressed and the most induced. All the genes encoding for enzymes of the isoflavonoid pathway were also strongly induced; this was paralleled by a marked accumulation of vestitol and isoliquiritigenin. Moreover, accumulation of several other isoflavonoids was also detected. In vitro measurements of the free radical scavenging capacity of vestitol indicated that this compound can be an appropriate free radical scavenger, suggesting a possible role for this molecule in the response to abiotic stress. On the other hand, an increase of flavonol levels was not observed while the expression of the key enzymes for flavonol biosynthesis flavanone-3-hydroxylase and flavonol synthase was decreased. Taken together, these results indicate that L. japonicus follows a peculiar strategy in its response to UV radiation by accumulating isoflavonoids as an possible alternative to accumulation of flavonols as observed in other plant species.

Stepwise response of MeJA-induced genes and pathways in leaves of C. roseus

Catharanthus roseus is a perennial herb known for the production of important terpenoid indole alkaloids (TIAs) in addition to a variety of phenolic compounds. The goal of the present work was to detect the prolonged effects of MeJA (6 uM) treatment across time (up to 24 days) in order to detect the stepwise response of MeJA-induced genes and pathways in leaves of C. rouses. Prolonged exposure of plants to MeJA (6 uM) treatment for different time points (6, 12 and 24 days) indicated that genes in the indole alkaloid biosynthesis pathway and upstream pathways were triggered earlier (e.g., 6 days) than those in the anthocyanin biosynthesis pathway and its upstream pathways (e.g., 12 days). Three enzymes, e.g., T16H, OMT, and D4H, in the six-step vindoline biosynthesis and two enzymes, e.g., TDC and STR, acting consecutively in the conversion of tryptophan to strictosidine, were activated after 6 days of MeJA treatment. Two other key enzymes, e.g., TRP and CYP72A1, acting concurrently upstream of the TIA biosynthesis pathway were upregulated after 6 days. The genes encoding TDC and STR might concurrently act as a master switch of the TIA pathway towards the production of the indole alkaloids. On the other hand, we speculate that the gene encoding PAL enzyme also acts as the master switch of phenylpropanoid biosynthesis and the downstream flavonoid biosynthesis and anthocyanin biosynthesis pathways towards the production of several phenolic compounds. PAL and the downstream enzymes were activated 12 days after treatment. Cluster analysis confirmed the concordant activities of the flower- and silique-specific bHLH25 transcription factor and the key enzyme in the TIA biosynthesis pathway, e.g., STR. Due to the stepwise response of the two sets of pathways, we speculate that enzymes activated earlier likely make TIA biosynthesis pathway a more favourable target in C. roseus than anthocyanin biosynthesis pathway.

A Comparative Metabolomics Analysis Reveals the Tissue-Specific Phenolic Profiling in Two Acanthopanax Species

Acanthopanax senticosus (Rupr. Maxim.) Harms (ASH) and Acanthopanax sessiliflorus (Rupr. Maxim.) Seem (ASS), are members of the Araliaceae family, and both are used in Asian countries. These herbals have drawn much attention in recent years due to their strong biological activity, with innocuity and little side effects. However, the common and distinct mode of compound profiles between ASH and ASS is still unclear. In this study, a high performance liquid chromatograph-mass spectrometry (HPLC-MS) method was developed to simultaneously quantify the seven major active compounds, including protocatechuate, eleutheroside B, eleutheroside E, isofraxidin, hyperoside, kaempferol and oleanolic acid. Then the targeted metabolomics were conducted to identify 19 phenolic compounds, with tight relation to the above mentioned active compounds, including nine C6C3C6-type, six C6C3-type and four C6C1-type in the two Acanthopanax species studied here. The results showed that the seven active compounds presented a similar trend of changes in different tissues, with more abundant accumulation in roots and stems for both plants. From the view of plant species, the ASH plants possess higher abundance of compounds, especially in the tissues of roots and stems. For phenolics, the 19 phenols detected here could be clearly grouped into five main clusters based on their tissue-specific accumulation patterns. Roots are the tissue for the most abundance of their accumulations. C6C3C6-type compounds are the most widely existing type in both plants. In conclusion, the tissue- and species-specificity in accumulation of seven active compounds and phenolics were revealed in two Acanthopanax species.

Lipidomics Unravels the Role of Leaf Lipids in Thyme Plant Response to Drought Stress

Thymus is one of the best known genera within the Labiatae (Lamiaceae) family, with more than 200 species and many medicinal and culinary uses. The effects of prolonged drought on lipid profile were investigated in tolerant and sensitive thyme plants (Thymus serpyllum L. and Thymus vulgaris L., respectively). Non-targeted non-polar metabolite profiling was carried out using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry with one-month-old plants exposed to drought stress, and their morpho-physiological parameters were also evaluated. Tolerant and sensitive plants exhibited clearly different responses at a physiological level. In addition, different trends for a number of non-polar metabolites were observed when comparing stressed and control samples, for both sensitive and tolerant plants. Sensitive plants showed the highest decrease (55%) in main lipid components such as galactolipids and phospholipids. In tolerant plants, the level of lipids involved in signaling increased, while intensities of those induced by stress (e.g., oxylipins) dramatically decreased (50–60%), in particular with respect to metabolites with m/z values of 519.3331, 521.3488, and 581.3709. Partial least square discriminant analysis separated all the samples into four groups: tolerant watered, tolerant stressed, sensitive watered and sensitive stressed. The combination of lipid profiling and physiological parameters represented a promising tool for investigating the mechanisms of plant response to drought stress at non-polar metabolome level.

Deep Sequencing of Suppression Subtractive Hybridisation Drought and Recovery Libraries of the Non-model Crop Trifolium repens L

White clover is a short-lived perennial whose persistence is greatly affected by abiotic stresses, particularly drought. The aim of this work was to characterize its molecular response to water deficit and recovery following re-hydration to identify targets for the breeding of tolerant varieties. We created a white clover reference transcriptome of 16,193 contigs by deep sequencing (mean base coverage 387x) four Suppression Subtractive Hybridization (SSH) libraries (a forward and a reverse library for each treatment) constructed from young leaf tissue of white clover at the onset of the response to drought and recovery. Reads from individual libraries were then mapped to the reference transcriptome and processed comparing expression level data. The pipeline generated four robust sets of transcripts induced and repressed in the leaves of plants subjected to water deficit stress (6,937 and 3,142, respectively) and following re-hydration (6,695 and 4,897, respectively). Semi-quantitative polymerase chain reaction was used to verify the expression pattern of 16 genes. The differentially expressed transcripts were functionally annotated and mapped to biological processes and pathways. In agreement with similar studies in other crops, the majority of transcripts up-regulated in response to drought belonged to metabolic processes, such as amino acid, carbohydrate, and lipid metabolism, while transcripts involved in photosynthesis, such as components of the photosystem and the biosynthesis of photosynthetic pigments, were up-regulated during recovery. The data also highlighted the role of raffinose family oligosaccharides (RFOs) and the possible delayed response of the flavonoid pathways in the initial response of white clover to water withdrawal. The work presented in this paper is to our knowledge the first large scale molecular analysis of the white clover response to drought stress and re-hydration. The data generated provide a valuable genomic resource for marker discovery and ultimately for the improvement of white clover.

The Combined Effects of Ethylene and MeJA on Metabolic Profiling of Phenolic Compounds in Catharanthus roseus Revealed by Metabolomics Analysis

Phenolic compounds belong to a class of secondary metabolites and are implicated in a wide range of responsive mechanisms in plants triggered by both biotic and abiotic elicitors. In this study, we approached the combinational effects of ethylene and MeJA (methyl jasmonate) on phenolic compounds profiles and gene expressions in the medicinal plant Catharanthus roseus. In virtue of a widely non-targeted metabolomics method, we identified a total of 34 kinds of phenolic compounds in the leaves, composed by 7 C6C1-, 11 C6C3-, and 16 C6C3C6 compounds. In addition, 7 kinds of intermediates critical for the biosynthesis of phenolic compounds and alkaloids were identified and discussed with phenolic metabolism. The combinational actions of ethylene and MeJA effectively promoted the total phenolic compounds, especially the C6C1 compounds (such as salicylic acid, benzoic acid) and C6C3 ones (such as cinnamic acid, sinapic acid). In contrast, the C6C3C6 compounds displayed a notably inhibitory trend in this case. Subsequently, the gene-to-metabolite networks were drawn up by searching for correlations between the expression profiles of 5 gene tags and the accumulation profiles of 41 metabolite peaks. Generally, we provide an insight into the controlling mode of ethylene-MeJA combination on phenolic metabolism in C. roseus leaves.

Use of transcriptomics and co-expression networks to analyze the interconnections between nitrogen assimilation and photorespiratory metabolism

Nitrogen is one of the most important nutrients for plants and, in natural soils, its availability is often a major limiting factor for plant growth. Here we examine the effect of different forms of nitrogen nutrition and of photorespiration on gene expression in the model legume Lotus japonicus with the aim of identifying regulatory candidate genes co-ordinating primary nitrogen assimilation and photorespiration. The transcriptomic changes produced by the use of different nitrogen sources in leaves of L. japonicus plants combined with the transcriptomic changes produced in the same tissue by different photorespiratory conditions were examined. The results obtained provide novel information on the possible role of plastidic glutamine synthetase in the response to different nitrogen sources and in the C/N balance of L. japonicus plants. The use of gene co-expression networks establishes a clear relationship between photorespiration and primary nitrogen assimilation and identifies possible transcription factors connected to the genes of both routes.