The role of chalcone synthase in the regulation of flavonoid biosynthesis in developing oat primary leaves

Rhizophagus Irregularis regulates flavonoids metabolism in paper mulberry roots under cadmium stress

Broussonetia papyrifera is widely found in cadmium (Cd) contaminated areas, with an inherent enhanced flavonoids metabolism and inhibited lignin biosynthesis, colonized by lots of symbiotic fungi, such as arbuscular mycorrhizal fungi (AMF). However, the physiological and molecular mechanisms by which Rhizophagus irregularis, an AM fungus, regulates flavonoids and lignin in B. papyrifera under Cd stress remain unclear. Here, a pot experiment of B. papyrifera inoculated and non-inoculated with R. irregularis under Cd stress was carried out. We determined flavonoids and lignin concentrations in B. papyrifera roots by LC-MS and GC-MS, respectively, and measured the transcriptional levels of flavonoids- or lignin-related genes in B. papyrifera roots, aiming to ascertain the key components of flavonoids or lignin, and key genes regulated by R. irregularis in response to Cd stress. Without R. irregularis, the concentrations of eriodictyol, quercetin and myricetin were significantly increased under Cd stress. The concentrations of eriodictyol and genistein were significantly increased by R. irregularis, while the concentration of rutin was significantly decreased. Total lignin and lignin monomer had no alteration under Cd stress or with R. irregularis inoculation. As for flavonoids- or lignin-related genes, 26 genes were co-regulated by Cd stress and R. irregularis. Among these genes, BpC4H2, BpCHS8 and BpCHI5 were strongly positively associated with eriodictyol, indicating that these three genes participate in eriodictyol biosynthesis and were involved in R. irregularis assisting B. papyrifera to cope with Cd stress. This lays a foundation for further research revealing molecular mechanisms by which R. irregularis regulates flavonoids synthesis to enhance tolerance of B. papyrifera to Cd stress.

Improvement of Chalcone Synthase Activity and High-Efficiency Fermentative Production of (2S)-Naringenin via In Vivo Biosensor-Guided Directed Evolution

Chalcone synthase (CHS) catalyzes the rate-limiting step of (2S)-naringenin (the essential flavonoid skeleton) biosynthesis. Improving the activity of the CHS by protein engineering enhances (2S)-naringenin production by microbial fermentation and can facilitate the production of valuable flavonoids. A (2S)-naringenin biosensor based on the TtgR operon was constructed in Escherichia coli and its detection range was expanded by promoter optimization to 0-300 mg/L, the widest range for (2S)-naringenin reported. The high-throughput screening scheme for CHS was established based on this biosensor. A mutant, SjCHS1S208N with a 2.34-fold increase in catalytic activity, was discovered by directed evolution and saturation mutagenesis. A pathway for de novo biosynthesis of (2S)-naringenin by SjCHS1S208N was constructed in Saccharomyces cerevisiae, combined with CHS precursor pathway optimization, increasing the (2S)-naringenin titer by 65.34% compared with the original strain. Fed-batch fermentation increased the titer of (2S)-naringenin to 2513 ± 105 mg/L, the highest reported so far. These findings will facilitate efficient flavonoid biosynthesis and further modification of the CHS in the future.

De novo biosynthesis of anticarcinogenic icariin in engineered yeast

Icariin (ICA) has wide applications in nutraceuticals and medicine with strong anticancer activities. However, the structural complexity and low abundance in plants of ICA lead to the unsustainable and high-cost supply from chemical synthesis and plant extraction. Here, the whole biosynthesis pathway of ICA was elucidated, then was constructed in Saccharomyces cerevisiae, including a 13-step heterologous ICA pathway from eleven kinds of plants as well as deletions or overexpression of ten yeast endogenous genes. Spatial regulation of 8-C-prenyltransferase to mitochondria and three-stage sequential control of 4'-O-methyltransferase, 3-OH rhamnosyltransferase, and 7-OH glycosyltransferase expression successfully achieved the de novo synthesis of ICA with a titer of 130 μg/L under shake-flask culture. The ICA synthesis from glucose represents the longest reconstructed pathway of flavonoid in microbe so far. This study provides a potential choice for the sustainable microbial production of number of complex flavonoids.

Cloning of a CHS gene of Poncirus trifoliata and its expression in response to soil water deficit and arbuscular mycorrhizal fungi

Flavonoids are secondary metabolites widely found in plants with antioxidants, of which chalcone synthase (CHS) is a key enzyme required in flavonoid synthesis pathways. The objective of this study was to clone a CHS gene from trifoliate orange (Poncirus trifoliata) and analyze its biological information and partial functions. A PtCHS gene (NCBI accession: MZ350874) was cloned from the genome-wide of trifoliate orange, which has 1156 bp in length, encoding 391 amino acids, with a predicted protein relative molecular mass of 42640.19, a theoretical isoelectric point of 6.28, and a lipid coefficient of 89.82. The protein is stable, hydrophilic, and high sequence conservation (92.49% sequence homology with CHS gene of other species). PtCHS was highly expressed in stems, leaves and flowers, but very low expression in roots and seeds. Soil water deficit could up-regulate expressions of PtCHS in leaves. An arbuscular mycorrhizal fungus, Funneliformis mosseae, significantly increased plant biomass production, CHS activity, expressions of PtCHS, and total flavonoid content in leaves and roots, independent of soil water status. Total flavonoids were significantly positively correlated with PtCHS expression in leaves only and also positively with root mycorrhizal colonization. Such results provide insight into the important functions of PtCHS in trifoliate orange.

Optimum chalcone synthase for flavonoid biosynthesis in microorganisms

Chalcones and the subsequently generated flavonoids, as well as flavonoid derivatives, have been proven to have a variety of physiological activities and are widely used in: the pharmaceutical, food, feed, and cosmetic industries. As the content of chalcones and downstream products in native plants is low, the production of these compounds by microorganisms has gained the attention of many researchers and has a history of more than 20 years. The mining and engineering of chalcone synthase (CHS) could be one of the most important ways to achieve more efficient production of chalcones and downstream products in microorganisms. CHS has a broad spectrum of substrates, and its enzyme activity and expression level can significantly affect the efficiency of the biosynthesis of flavonoids. This review summarizes the recent advances in the: structure, mechanism, evolution, substrate spectrum, transformation, and expression regulation in the flavonoid biosynthesis of this vital enzyme. Future development directions were also suggested. The findings may further promote the research and development of flavonoids and health products, making them vital in the fields of human diet and health.

Bioconversion of Callus-Produced Precursors to Silymarin Derivatives in Silybum marianum Leaves for the Production of Bioactive Compounds

The present study aimed to investigate the enzymatic potential of Silybum marianum leaves to bioconvert phenolic acids produced in S. marianum callus into silymarin derivatives as chemopreventive agent. Here we demonstrate that despite the fact that leaves of S. marianum did not accumulate silymarin themselves, expanding leaves had the full capacity to convert di-caffeoylquinic acid to silymarin complex. This was proven by HPLC separations coupled with electrospray ionization mass spectrometry (ESI-MS) analysis. Soaking the leaf discs with S. marianum callus extract for different times revealed that silymarin derivatives had been formed at high yield after 16 h. Bioconverted products displayed the same retention time and the same mass spectra (MS or MS/MS) as standard silymarin. Bioconversion was achieved only when using leaves of a specific age, as both very young and old leaves failed to produce silymarin from callus extract. Only medium leaves had the metabolic capacity to convert callus components into silymarin. The results revealed higher activities of enzymes of the phenylpropanoid pathway in medium leaves than in young and old leaves. It is concluded that cotyledon-derived callus efficiently produces compounds that can be bio-converted to flavonolignans in leaves tissue of S. marianum.

Hydroxysafflor Yellow A: A Systematical Review on Botanical Resources, Physicochemical Properties, Drug Delivery System, Pharmacokinetics, and Pharmacological Effects

Hydroxysafflower yellow A (HSYA), as a principal natural ingredient extracted from safflower (Carthamus tinctorius L.), has significant pharmacological activities, such as antioxidant, anti-inflammatory, anticoagulant, and anticancer effects. However, chemical instability and low bioavailability have been severely hampering the clinical applications of HSYA during the treatment of cardiovascular and cerebrovascular disease. Therefore, this present review systematically summarized the materials about HSYA, including acquisition methods, extraction and detection methods, pharmacokinetics, pharmacological effects and molecular mechanism, especially focus on the possible causes and resolutions about the chemical instability and low bioavailability of HSYA, in order to provide relatively comprehensive basic data for the related research of HSYA.

Differential interaction of the dark septate endophyte Cadophora sp. and fungal pathogens in vitro and in planta

Dark septate endophytes (DSEs) present a group of widespread root-colonizing fungi. The role of these endophytes in ecosystems and their interactions with plant pathogens are not well understood. In the current study, we assessed the antagonistic potential of the model DSE Cadophora sp. against the tomato soilborne pathogens Rhizoctonia solani, Pythium aphanidermatum and Verticillium dahliae. To investigate their interactions, we conducted in vitro assays followed by a greenhouse experiments in which tomato plants were inoculated with different combinations of the DSE and pathogens. RNA accumulation of selected tomato pathogenesis-related genes and of Cadophora sp. genes with putative antifungal function was analyzed. Cadophora sp. inhibited the growth of the fungal pathogens in vitro and vice versa; a negative impact of the pathogens on the growth of the DSE was also detected. In roots, however, this mutual negative interaction could not be observed. Expression analyses of plant genes could not explain this differential effect, but among the Cadophora sp. genes analyzed, a gene coding for a chalcone synthase was downregulated in planta. The data indicate that plants can change the interaction between fungi and, therefore, in vitro detected antagonism does not necessarily reflect the situation inside the plant.

Improving acetyl-CoA biosynthesis in Saccharomyces cerevisiae via the overexpression of pantothenate kinase and PDH bypass

BACKGROUND

Acetyl-CoA is an important precursor in Saccharomyces cerevisiae. Various approaches have been adopted to improve its cytosolic level previously with the emphasis on engineering the "acetyl-" part of acetyl-CoA. To the best of our knowledge, there have been no reports on engineering the "-CoA" part so far.

RESULTS

In this study, we had tried to engineer S. cerevisiae from both the "-CoA" part via pantothenate kinase overexpression (PanK from S. cerevisiae, the rate-limiting enzyme for CoA synthesis) and the "acetyl-"part through PDH bypass introduction (ALD6 from S. cerevisiae and SeAcs^L641P from Salmonella enteric). A naringenin-producing reporter strain had been constructed to reflect cytosolic acetyl-CoA level as acetyl-CoA is the precursor of naringenin. It was found that PanK overexpression or PDH bypass introduction alone only led to a twofold or 6.74-fold increase in naringenin titer, but the combination of both (strain CENFPAA01) had resulted in 24.4-fold increase as compared to the control (strain CENF09) in the presence of 0.5 mM substrate p-coumaric acid. The supplement of PanK substrate pantothenate resulted in another 19% increase in naringenin production.

CONCLUSIONS

To greatly enhance acetyl-CoA level in yeast cytosol, it is feasible to engineer both the "acetyl-" part and the "-CoA" part simultaneously. Insufficient CoA supply might aggravate acetyl-CoA shortage and cause low yield of target product.

Analysis of response mechanism in soybean under low oxygen and flooding stresses using gel-base proteomics technique

A proteomics approach was used to analyze the response mechanism in soybean seedlings under low oxygen and flooding stresses. Three-day-old soybean seedlings were subjected to low oxygen and flooding stresses. Growth of root was suppressed in both stresses with more extent of suppression in flooded seedlings at 3 and 6 days following the treatments. Proteins were extracted from roots and separated by two-dimensional polyacrylamide gel electrophoresis. Of total 1,233 protein spots, 27 protein spots were commonly changed under low oxygen and flooding stresses; while the differential change in 4 and 18 protein spots was specific to low oxygen and flooding stresses, respectively. Proteins related to metabolism and energy were increased; while protein destination/storage related proteins were decreased commonly under low oxygen and flooding stresses. Protein specie, TCP domain class transcription factor was decreased specifically under low oxygen stress; while decrease of nine proteins related to metabolism, protein destination/storage and disease/defense was specific in flooded seedlings. The decrease in majority of the proteins related to protein destination/storage specifically in flooded seedlings implies the misfolding of proteins resulting in flooded injuries in an independent way of oxygen deprivation. These results suggest that decrease in proteins related to protein destination/storage and disease/defense causes more growth suppression in soybean seedlings under flooding stress compared to low oxygen stress.

A set of regioselective O-methyltransferases gives rise to the complex pattern of methoxylated flavones in sweet basil

Polymethoxylated flavonoids occur in a number of plant families, including the Lamiaceae. To date, the metabolic pathways giving rise to the diversity of these compounds have not been studied. Analysis of our expressed sequence tag database for four sweet basil (Ocimum basilicum) lines afforded identification of candidate flavonoid O-methyltransferase genes. Recombinant proteins displayed distinct substrate preferences and product specificities that can account for all detected 7-/6-/4'-methylated, 8-unsubstituted flavones. Their biochemical specialization revealed only certain metabolic routes to be highly favorable and therefore likely in vivo. Flavonoid O-methyltransferases catalyzing 4'- and 6-O-methylations shared high identity (approximately 90%), indicating that subtle sequence changes led to functional differentiation. Structure homology modeling suggested the involvement of several amino acid residues in defining the proteins' stringent regioselectivities. The roles of these individual residues were confirmed by site-directed mutagenesis, revealing two discrete mechanisms as a basis for the switch between 6- and 4'-O-methylation of two different substrates. These findings delineate major pathways in a large segment of the flavone metabolic network and provide a foundation for its further elucidation.

Accumulation of tilianin and rosmarinic acid and expression of phenylpropanoid biosynthetic genes in Agastache rugosa

Korean mint (Agastache rugosa), a perennial, medicinal plant of the Labiatae family, has many useful constituents, including monoterpenes and phenylpropanoids. Among these, tilianin and rosmarinic acid, 2 well-known natural products, have many pharmacologically useful properties. Chalcone synthase (CHS) and chalcone isomerase (CHI) catalyze the first and second committed steps in the phenylpropanoid pathway of plants, leading to the production of tilianin. In this study, cDNAs encoding CHS (ArCHS) and CHI (ArCHI) were isolated from A. rugosa using rapid amplification of cDNA ends (RACE)-PCR. Amino acid sequence alignments showed that ArCHS and ArCHI shared high sequence identity and active sites with their respective orthologous genes. Quantitative real-time PCR analysis was used to determine the expression levels of genes involved in tilianin and rosmarinic acid biosyntheses in the flowers, leaves, stems, and roots of A. rugosa. High-performance liquid chromatography (HPLC) revealed that the accumulation pattern of tilianin matched the expression patterns of ArCHS and ArCHI in different organs of A. rugosa. Moreover, acacetin, the precursor of tilianin, also demonstrated an accumulation pattern congruent with the expression of these 2 genes. The transcription levels of ArPAL, ArC4H, and Ar4CL were the highest in the leaves or flowers of the plant, which also contained a relatively high amount of rosmarinic acid. However, the roots showed a significant content of rosmarinic acid, although the transcription of ArPAL, ArC4H, and Ar4CL were low. The findings of our study support the medicinal usefulness of A. rugosa and indicate targets for increasing tilianin and rosmarinic acid production in this plant.

Quantitative trait loci and metabolic pathways: genetic control of the concentration of maysin, a corn earworm resistance factor, in maize silks

Interpretation of quantitative trait locus (QTL) studies of agronomic traits is limited by lack of knowledge of biochemical pathways leading to trait expression. To more fully elucidate the biological significance of detected QTL, we chose a trait that is the product of a well-characterized pathway, namely the concentration of maysin, a C-glycosyl flavone, in silks of maize, Zea mays L. Maysin is a host-plant resistance factor against the corn earworm, Helicoverpa zea (Boddie). We determined silk maysin concentrations and restriction fragment length polymorphism genotypes at flavonoid pathway loci or linked markers for 285 F2 plants derived from the cross of lines GT114 and GT119. Single-factor analysis of variance indicated that the p1 region on chromosome 1 accounted for 58.0% of the phenotypic variance and showed additive gene action. The p1 locus is a transcription activator for portions of the flavonoid pathway. A second QTL, represented by marker umc 105a near the brown pericarp1 locus on chromosome 9, accounted for 10.8% of the variance. Gene action of this region was dominant for low maysin, but was only expressed in the presence of a functional p1 allele. The model explaining the greatest proportion of phenotypic variance (75.9%) included p1, umc105a, umc166b (chromosome 1), r1 (chromosome 10), and two epistatic interaction terms, p1 x umc105a and p1 x r1. Our results provide evidence that regulatory loci have a central role and that there is a complex interplay among different branches of the flavonoid pathway in the expression of this trait.

Dynamics of auxin movement in the gravistimulated leaf-sheath pulvinus of oat (Avena sativa)

The role of auxin redistribution in the graviresponse of the leaf-sheath pulvinus of oat (Avena sativa L.) was assessed using 3H-indole-3-acetic acid (3H-IAA) preloaded into isolated pulvini. When pulvini were totally isolated from subtending nodal tissue as well as leaf-sheath and internode, gravistimulation failed to induce an asymmetric growth response. Presence of either the nodal tissue or the internode/leaf-sheath tissue was sufficient to restore a normal graviresponse. Gravistimulation of totally isolated pulvini inhibited basipetal export of label (i.e., 3H-IAA) without generating any asymmetry of label within the pulvinus. In contrast, gravistimulation of pulvini with nodes intact generated an asymmetric distribution of label (initiation by 1 h; final ratio, lower/upper = 1.5) as well as the upward bending response. The kinetics of formation of the asymmetry of label paralleled the kinetics of initiation of the asymmetric growth response. The addition of 0.1 M sucrose to all agar blocks shortened both the time to initiation of label redistribution and the time to initial upward bending. However, sucrose did not change the final magnitude of label asymmetry although it increased the final steady state bending rate four fold. The inhibitors of polar auxin transport N-1-naphthylphthalamaic acid (NPA), 2,3,5-triiodobenzoic acid (TIBA), morphactin, naringenin, kaempferol and myricetin all significantly decreased the bending response of oat pulvini, but this inhibition was less than 50%. In contrast, TIBA and naringenin (each at 100 micromoles), effectively eliminated the redistribution of label, but did not eliminate the bending response. These results indicate that the active basipetal export of auxin is inhibited by gravistimulation of the oat pulvinus, while active lateral transport is induced. It is concluded that, while lateral transport of auxin occurs following gravistimulation, it is not necessary for a graviresponse. Other processes, such as localized changes in tissue responsiveness or the conversion of conjugated hormone to free (active) hormone, may suffice to drive the graviresponse.

Cloning and molecular characterization of the chalcone synthase multigene family of Petunia hybrida

Chalcone synthase-encoding genes (chs) in Petunia hybrida comprise a multigene family. Some of the chs genes have been grouped into a subfamily, based upon their strong cross-hybridization and tight genomic linkage. From genomic libraries eight 'complete' chs genes, two chs gene 5'-fragments and two chs gene 3'-fragments have been isolated. The nucleotide sequence of six complete chs genes is presented and discussed in relation to their evolutionary origin and expression in different tissues. Each member of the family consists of two exons separated by an intron of variable size and sequence, which is located at a conserved position. The chs gene fragments represent single exons. Homology between non-linked chs genes is approx. 80% at the DNA level and restricted to protein-coding sequences. Homology between subfamily members (which are tightly linked) is higher (90-99%) and extends into untranslated regions of the gene, strengthening the view that they arose by recent gene duplications. The chsD gene contains a mutated translation stop codon, suggesting that this is an inactive (pseudo)gene. None of the other members of the gene family exhibits characteristics of a pseudogene, indicating that if gene inactivation has occurred during their evolution, it must characteristics of a pseudogene, indicating that if gene inactivation has occurred during their evolution, it must have been a recent event. Homology at the protein level between some (expressed) chs genes is surprisingly low. The possibility that these genes encode proteins with slightly different enzymatic activities is discussed.

Differential regulation of soybean chalcone synthase genes in plant defence, symbiosis and upon environmental stimuli

Four independent recombinant lambda clones hybridizing to parsley chalcone synthase (CHS) cDNA were isolated from a soybean (Glycine max) genomic library. Restriction fragment length polymorphism (RFLP) analysis indicated that the CHS gene family comprises six members. The CHS genes were found to be clustered with three genes on a 10 kb segment and pairs on others. DNA sequences of the 5'-, the coding-, and the 3' untranslated regions were determined for three different genes. A consensus alignment of the 5' regions revealed extensive homology between them for up to 150 bp upstream of the TATA box. Developmental regulation of CHS was observed in uninfected and in rhizobium-infected roots. Regulation at the level of transcription by different stimuli was investigated in the root, stem and cotyledons of soybean seedlings. Our results suggest a co-operative induction of CHS genes by wounding and elicitor treatment of cotyledons. The most rapid transcript accumulation, however, was observed in roots and stems. The induction of CHS genes by light was found to be UV dependent. A possible involvement of different members of the CHS gene family in response to elicitor versus UV treatment was analysed by the use of gene specific probes, and unexpectedly revealed that only CHS 1 transcription was induced by either elicitor or UV treatment of seedlings.

Time courses for phytochrome-induced enzyme levels in phenylpropanoid metabolism (phenylalanine ammonia-lyase, naringenin-chalcone synthase) compared with time courses for phytochrome-mediated end-product accumulation (anthocyanin, quercetin)

Time course for changes in the levels of enzymes characteristic of general phenylpropanoid metabolism (phenylalanine ammonia-lyase, PAL; EC 4.3.1.5) and of the flavonoid-glycoside branch pathway (naringenin-chalcone synthase, CHS; EC 2.3.1.74) were measured in the cotyledons of mustard (Sinapis alba L.) seedlings and compared with the rates of accumulation of related end products (anthocyanin and quercetin). Induction of enzyme levels and of end-product accumulation was carried out with red and far-red (FR) light, operating via phytochrome. The data are compatible with the concept that the phytochrome-mediated appearance of enzymes such as PAL and CHS is indeed a prerequisite for the appearance of anthocyanins and flavonols. However, there is no close correlation between enzyme levels and the rates of synthesis of end products which could justify the identification of specific rate-limiting enzymes. Rather, the data indicate that there is a second phytochrome-dependent step, beyond enzyme induction, where the actual rate of flavonoid accumulation is determined. Anthocyanin and quercetin accumulation respond differently to light. However, the relative action of continuous FR, red light pulses and 'stored phytochrome signal' is the same in both cases. This indicates that the mode of operation of phytochrome is the same in both cases. The two syntheses differ only in the degree of responsiveness towards phytochrome. The time course for changes in CHS levels in continuous FR, i.e. under conditions of phytochrome photosteady state, is similar to the time course for PAL levels whereas the time courses in darkness, following transfer from FR to darkness, are totally different. In the case of CHS, a transient rise is observed whereas, with PAL, an instantaneous drop in enzyme level occurs after transfer from FR to darkness. It is concluded that the 'stored phytochrome signal' operates in darkness in the case of CHS but not in the case of PAL.

Chalcone synthases from spinach (Spinacia oleracea L.) : I. Purification, peptide patterns, and immunological properties of different forms

The two chalcone-synthase forms from leaves ofSpinacia oleracea L. were purified to apparent homogeneity. Antibodies were raised against both proteins in rabbits. The specificity of the antibodies was tested using immunotitration, immunoblotting, and immunoelectrophoresis techniques. The antibodies exhibited exclusive specificity for chalcone synthase and did not discriminate between the two antigens. The homodimeric chalcone synthases had the same subunit molecular weight but differed in their apparent native molecular weights. The peptide maps indicated extensive homology between the proteins. Chalcone-synthase activity was not detected in isolated spinach chloroplasts. Both enzyme forms were present in spinach cell-suspension cultures in which they were induced by light.