Cinnamic acid 4-hydroxylase mechanism-based inactivation by psoralen derivatives: cloning and characterization of a C4H from a psoralen producing plant-Ruta graveolens-exhibiting low sensitivity to psoralen inactivation

Convergent evolution of the UbiA prenyltransferase family underlies the independent acquisition of furanocoumarins in plants

Furanocoumarins (FCs) are plant-specialized metabolites with potent allelochemical properties. The distribution of FCs is scattered with a chemotaxonomical tendency towards four distant families with highly similar FC pathways. The mechanism by which this pathway emerged and spread in plants has not been elucidated. Furanocoumarin biosynthesis was investigated in Ficus carica (fig, Moraceae), focusing on the first committed reaction catalysed by an umbelliferone dimethylallyltransferase (UDT). Comparative RNA-seq analysis among latexes of different fig organs led to the identification of a UDT. The phylogenetic relationship of this UDT to previously reported Apiaceae UDTs was evaluated. The expression pattern of F. carica prenyltransferase 1 (FcPT1) was related to the FC contents in different latexes. Enzymatic characterization demonstrated that one of the main functions of FcPT1 is UDT activity. Phylogenetic analysis suggested that FcPT1 and Apiaceae UDTs are derived from distinct ancestors, although they both belong to the UbiA superfamily. These findings are supported by significant differences in the related gene structures. This report describes the identification of FcPT1 involved in FC biosynthesis in fig and provides new insights into multiple origins of the FC pathway and, more broadly, into the adaptation of plants to their environments.

Convergent evolution leading to the appearance of furanocoumarins in citrus plants

Furanocoumarins are defense molecules mainly described in four plant families that are phylogenetically distant. Molecular characterization of the biosynthetic pathway has been started for many years in Apiaceae and Rutaceae. The results obtained thus far in Apiaceae indicated a major role of cytochromes P450 (P450s) in the CYP71 family. In the present work, we describe the importance of another subfamily of P450s, CYP82D, identified by using a deep analysis of the citrus (Rutaceae) genome and microarray database. CYP82D64 is able to hydroxylate xanthotoxin to generate 5-OH-xanthotoxin. Minor and limited amino acid changes in the CYP82D64 coding sequence between Citrus paradisi and Citrus hystrix provide the enzyme in the latter with the ability to hydroxylate herniarin, but with low efficiency. The kinetic constants of the enzyme are consistent with those of other enzymes of this type in plants and indicate that it may be the physiological substrate. The activity of the enzyme is identical to that of CYP71AZ6 identified in parsnip, showing possible evolutionary convergence between these two families of plants. It is highly possible that these molecules are derived from the synthesis of ubiquitous coumarins throughout the plant kingdom.

Pharmacokinetic-pharmacodynamic modeling to study the anti-dysmenorrhea effect of Guizhi Fuling capsule on primary dysmenorrhea rats

BACKGROUND

Primary dysmenorrhea (PDM) is one of the most common gynaecological disorders among women, which seriously affects women's life quality due to its high incidence rate. Guizhi Fuling capsule (GZFLC), a well-known traditional Chinese medical prescription, has been widely used to treat gynecological blood stasis syndromes such as PDM. However, its mechanisms of action and combination were still unknown.

PURPOSE

The aim of this study was to develop a pharmacokinetic-pharmacodynamic (PK-PD) model to assess time-concentration-effect relationships for anti-dysmenorrhea effect of GZFLC and provide better understanding for mechanisms of action and combination of GZFLC.

STUDY DESIGN AND METHODS

The PDM rats model was induced by oxytocin exposure following estradiol benzoate pretreatment. Gallic acid (GA), amygdalin (AMY), albiflorin (ALB), prunasin (PA) and cinnamic acid (CA) were evaluated as bioactive ingredients for investigating PK processes. GA, AMY, ALB and PA exhibited appropriate PK parameters and were selected as the PK markers to map the anti-dysmenorrhea effect of GZFLC. A PK-PD model was established on the basis of GA, AMY, ALB and PA plasma concentrations vs. the values of two ratios (PGE₂/PGF_2α and 6-Keto-PGF_1α/TXB₂), by a two-compartment PK model with a simple E_max model to explain the time delay between the drug plasma concentrations of PK markers and the anti-dysmenorrhea effect.

RESULTS

The PDM rat model has been successfully established. Compared with the normal treated group, the bioactive ingredients in PDM treated group exhibited significant changing trends of PK behaviors, such as better absorption and distribution, slower elimination and delays in reaching the maximum concentration (T_max). The analysis of PK-PD parameters indicated that the active metabolites and prototypes of bioactive ingredients in GZFLC were inclined to regulate the activity of prostacyclin synthetase and thromboxane synthetase to control the production of TXA₂ and PGI₂ so as to treat PDM. As the main effective medicinal materials for the treatment of PDM in GZFLC prescription Persicae Semen, Moutan Cortex and Paeonia lactiflora Pall, Persicae Semen played the most important role, while the role of Paeonia lactiflora Pall was the weakest.

CONCLUSION

The PK-PD model results provided scientific basis for clarifying compatibility mechanisms of GZFLC prescription and a better understanding for biosynthetic mechanisms of four prostaglandins (PGE₂, PGF_2α, 6-Keto-PGF_1α and TXB₂) in the treatment of PDM by GZFLC. Investigations on the relationship between the effects and the bioactive ingredients are of benefit to explore the mechanisms of action and combination for traditional Chinese medical prescriptions (TCP) and facilitate the development of future clinical applications of TCP.

The isolation and functional characterization of three liverwort genes encoding cinnamate 4-hydroxylase

The plant phenylpropanoid pathway is responsible for the synthesis of a wide variety of secondary metabolites. The second step in phenylpropanoid synthesis is carried out by the cytochrome P450 monooxygenase enzyme cinnamate 4-hydroxylase (C4H), which catalyzes the p-hydroxylation of trans-cinnamic acid to p-coumarate. Genes encoding C4H have been characterized in many vascular plant species, but as yet not in any bryophyte species. Here, a survey of the transcriptome sequences of four liverwort species was able to identify eight putative C4Hs. The three liverwort C4H genes taken forward for isolation and functional characterization were harbored by Plagiochasma appendiculatum (PaC4H) and Marchantia paleacea (MpC4H1 and MpC4H2). When the genes were heterologously expressed in yeast culture, an assay of enzyme activity indicated that PaC4H and MpC4H1 had a higher level of activity than MpC4H2. The favored substrate (trans-cinnamic acid) of all three liverwort C4Hs was the same as that of higher plant C4Hs. The co-expression of PaC4H in yeast cells harboring PaPAL (a P. appendiculatum ene encoding phenylalanine ammonia lyase) allowed the conversion of L-phenylalanine to p-coumaric acid. Furthermore, the expression level of PaC4H was enhanced after treatment with abiotic stress inducers UV irradiation or salicylic acid in the thallus of P. appendiculatum. The likelihood is that high activity C4Hs evolved in the liverworts and have remained highly conserved across the plant kingdom.

The Distribution of Coumarins and Furanocoumarins in Citrus Species Closely Matches Citrus Phylogeny and Reflects the Organization of Biosynthetic Pathways

Citrus plants are able to produce defense compounds such as coumarins and furanocoumarins to cope with herbivorous insects and pathogens. In humans, these chemical compounds are strong photosensitizers and can interact with medications, leading to the "grapefruit juice effect". Removing coumarins and furanocoumarins from food and cosmetics imply additional costs and might alter product quality. Thus, the selection of Citrus cultivars displaying low coumarin and furanocoumarin contents constitutes a valuable alternative. In this study, we performed ultra-performance liquid chromatography coupled with mass spectrometry analyses to determine the contents of these compounds within the peel and the pulp of 61 Citrus species representative of the genetic diversity all Citrus. Generally, Citrus peel contains larger diversity and higher concentrations of coumarin/furanocoumarin than the pulp of the same fruits. According to the chemotypes found in the peel, Citrus species can be separated into 4 groups that correspond to the 4 ancestral taxa (pummelos, mandarins, citrons and papedas) and extended with their respective secondary species descendants. Three of the 4 ancestral taxa (pummelos, citrons and papedas) synthesize high amounts of these compounds, whereas mandarins appear practically devoid of them. Additionally, all ancestral taxa and their hybrids are logically organized according to the coumarin and furanocoumarin pathways described in the literature. This organization allows hypotheses to be drawn regarding the biosynthetic origin of compounds for which the biogenesis remains unresolved. Determining coumarin and furanocoumarin contents is also helpful for hypothesizing the origin of Citrus species for which the phylogeny is presently not firmly established. Finally, this work also notes favorable hybridization schemes that will lead to low coumarin and furanocoumarin contents, and we propose to select mandarins and Ichang papeda as Citrus varieties for use in creating species devoid of these toxic compounds in future breeding programs.

A coumarin-specific prenyltransferase catalyzes the crucial biosynthetic reaction for furanocoumarin formation in parsley

Furanocoumarins constitute a sub-family of coumarin compounds with important defense properties against pathogens and insects, as well as allelopathic functions in plants. Furanocoumarins are divided into two sub-groups according to the alignment of the furan ring with the lactone structure: linear psoralen and angular angelicin derivatives. Determination of furanocoumarin type is based on the prenylation position of the common precursor of all furanocoumarins, umbelliferone, at C6 or C8, which gives rise to the psoralen or angelicin derivatives, respectively. Here, we identified a membrane-bound prenyltransferase PcPT from parsley (Petroselinum crispum), and characterized the properties of the gene product. PcPT expression in various parsley tissues is increased by UV irradiation, with a concomitant increase in furanocoumarin production. This enzyme has strict substrate specificity towards umbelliferone and dimethylallyl diphosphate, and a strong preference for the C6 position of the prenylated product (demethylsuberosin), leading to linear furanocoumarins. The C8-prenylated derivative (osthenol) is also formed, but to a much lesser extent. The PcPT protein is targeted to the plastids in planta. Introduction of this PcPT into the coumarin-producing plant Ruta graveolens showed increased consumption of endogenous umbelliferone. Expression of PcPT and a 4-coumaroyl CoA 2'-hydroxylase gene in Nicotiana benthamiana, which does not produce furanocoumarins, resulted in formation of demethylsuberosin, indicating that furanocoumarin production may be reconstructed by a metabolic engineering approach. The results demonstrate that a single prenyltransferase, such as PcPT, opens the pathway to linear furanocoumarins in parsley, but may also catalyze the synthesis of osthenol, the first intermediate committed to the angular furanocoumarin pathway, in other plants.

Coumarin and furanocoumarin quantitation in citrus peel via ultraperformance liquid chromatography coupled with mass spectrometry (UPLC-MS)

Coumarins and furanocoumarins are secondary metabolites commonly found in citrus plants. These molecules are allelochemical compounds in plants that have controversial effects on humans, such as phototoxicity and the commonly described interactions with drugs, referred to as the "grapefruit juice effect". Thus, it is important to develop a reliable method to identify and quantitate the coumarins and furanocoumarins in citrus extracts. For this purpose, we herein describe an ultraperformance liquid chromatography coupled with mass spectrometry (UPLC-MS)-based method. We first developed a rapid UPLC method (20 min) to separate the isomers of each furanocoumarin. A subsequent single ion monitoring MS detection method was performed to distinguish between the molecules, which were possibly coeluting but had different molecular weights. The method was successfully used to separate and quantitate 6 coumarins and 21 furanocoumarins in variable amounts within peel extracts (flavedo and albedo) of 6 varieties of Citrus (sweet orange, lemon, grapefruit, bergamot, pummelo, and clementine). This method combines high selectivity and sensitivity in a rapid analysis and is useful for fingerprinting Citrus species via their coumarin and furanocoumarin contents.

Molecular characterization of ferulate 5-hydroxylase gene from kenaf (Hibiscus cannabinus L.)

The purpose of this study is to clone and characterize the expression pattern of a F5H gene encoding ferulate 5-hydroxylase in the phenylpropanoid pathway from kenaf (Hibiscus cannabinus L.). Kenaf is a fast-growing dicotyledonous plant valued for its biomass. F5H, a cytochrome P450-dependent monooxygenase (CYP84), is a key enzyme for syringyl lignin biosynthesis. The full length of the F5H ortholog was cloned and characterized. The full-length F5H ortholog consists of a 1,557-bp open reading frame (ORF) encoding 518 amino acids (GenBank Accession number JX524278). The deduced amino acid sequence showed that kenaf F5H had the highest similarity (78%) with that of Populus trichocarpa. Transcriptional analysis of F5H ortholog was conducted using quantitative real-time PCR during the developmental stages of various tissues and in response to various abiotic stresses. The highest transcript level of the F5H ortholog was observed in immature flower tissues and in early stage (6 week-old) of stem tissues, with a certain level of expression in all tissues tested. The highest transcript level of F5H ortholog was observed at the late time points after treatments with NaCl (48 h), wounding (24 h), cold (24 h), abscisic acid (24 h), and methyl jasmonate (24 h).

The evolution of phenylpropanoid metabolism in the green lineage

Phenolic secondary metabolites are only produced by plants wherein they play important roles in both biotic and abiotic defense in seed plants as well as being potentially important bioactive compounds with both nutritional and medicinal benefits reported for animals and humans as a consequence of their potent antioxidant activity. During the long evolutionary period in which plants have adapted to the environmental niches in which they exist (and especially during the evolution of land plants from their aquatic algal ancestors), several strategies such as gene duplication and convergent evolution have contributed to the evolution of this pathway. In this respect, diversity and redundancy of several key genes of phenolic secondary metabolism such as polyketide synthases, cytochrome P450s, Fe(2+)/2-oxoglutarate-dependent dioxygenases and UDP-glycosyltransferases have played an essential role. Recent technical developments allowing affordable whole genome sequencing as well as a better inventory of species-by-species chemical diversity have resulted in a dramatic increase in the number of tools we have to assess how these pathways evolved. In parallel, reverse genetics combined with detailed molecular phenotyping is allowing us to elucidate the functional importance of individual genes and metabolites and by this means to provide further mechanistic insight into their biological roles. In this review, phenolic metabolite-related gene sequences (for a total of 65 gene families including shikimate biosynthetic genes) are compared across 23 independent species, and the phenolic metabolic complement of various plant species are compared with one another, in attempt to better understand the evolution of diversity in this crucial pathway.

CYP98A22, a phenolic ester 3'-hydroxylase specialized in the synthesis of chlorogenic acid, as a new tool for enhancing the furanocoumarin concentration in Ruta graveolens

BACKGROUND

Furanocoumarins are molecules with proven therapeutic properties and are produced in only a small number of medicinal plant species such as Ruta graveolens. In vivo, these molecules play a protective role against phytophageous insect attack. Furanocoumarins are members of the phenylpropanoids family, and their biosynthetic pathway is initiated from p-coumaroyl coA. The enzymes belonging to the CYP98A cytochrome P450 family have been widely described as being aromatic meta-hydroxylases of various substrates, such as p-coumaroyl ester derivatives, and are involved in the synthesis of coumarins such as scopoletin. In furanocoumarin-producing plants, these enzymes catalyze the step directly downstream of the junction with the furanocoumarin biosynthetic pathway and might indirectly impact their synthesis.

RESULTS

In this work, we describe the cloning and functional characterization of the first CYP98A encoding gene isolated from R. graveolens. Using Nicotiana benthamiana as a heterologous expression system, we have demonstrated that this enzyme adds a 3-OH to p-coumaroyl ester derivatives but is more efficient to convert p-coumaroyl quinate into chlorogenic acid than to metabolize p-coumaroyl shikimate. Plants exposed to UV-B stress showed an enhanced expression level of the corresponding gene. The R. graveolens cyp98a22 open reading frame and the orthologous Arabidopsis thaliana cyp98a3 open reading frame were overexpressed in stable transgenic Ruta plants. Both plant series were analyzed for their production of scopoletin and furanocoumarin. A detailed analysis indicates that both genes enhance the production of furanocoumarins but that CYP98A22, unlike CYP98A3, doesn't affect the synthesis of scopoletin.

CONCLUSIONS

The overexpression of CYP98A22 positively impacts the concentration of furanocoumarins in R. graveolens. This gene is therefore a valuable tool to engineer plants with improved therapeutical values that might also be more resistant to phytophageous insects.

Mutations in the cinnamate 4-hydroxylase gene impact metabolism, growth and development in Arabidopsis

The initial reactions of the phenylpropanoid pathway convert phenylalanine to p-coumaroyl CoA, a branch point metabolite from which many phenylpropanoids are made. Although the second enzyme of this pathway, cinnamic acid 4-hydroxylase (C4H), is well characterized, a mutant for the gene encoding this enzyme has not yet, to our knowledge, been identified, presumably because knock-out mutations in this gene would have severe phenotypes. This work describes the characterization of an allelic series of Arabidopsis reduced epidermal fluorescence 3 (ref3) mutants, each of which harbor mis-sense mutations in C4H (At2g30490). Heterologous expression of the mutant proteins in Escherichia coli yields enzymes that exhibit P420 spectra, indicative of mis-folded proteins, or have limited ability to bind substrate, indicating that the mutations we have identified affect protein stability and/or enzyme function. In agreement with the early position of C4H in phenylpropanoid metabolism, ref3 mutant plants accumulate decreased levels of several different classes of phenylpropanoid end-products, and exhibit reduced lignin deposition and altered lignin monomer content. Furthermore, these plants accumulate a novel hydroxycinnamic ester, cinnamoylmalate, which is not found in the wild type. The decreased C4H activity in ref3 also causes pleiotropic phenotypes, including dwarfism, male sterility and the development of swellings at branch junctions. Together, these observations indicate that C4H function is critical to the normal biochemistry and development of Arabidopsis.

Combined effects of Psoralens and ultraviolet-B on growth, pigmentation and biochemical parameters of Abelmoschus esculentus L

The effects of pre-treatment of Psoralens (furocoumarin compounds) and supplemental ultraviolet-B (sUV-B) were studied on plant growth, photosynthetic and non-photosynthetic pigments, protein, phenylalanine ammonia lyase (PAL) activity and antioxidative defense potential as well as their ultimate effects on biomass production in Abelmoschus esculentus L. (Okra) plants. Psoralens are capable of absorbing radiant energy and stimulating the pigmentation of human skin when photo-activated in presence of UV-A or UV-B making them beneficial in the treatment of vitilago. Pre-treatment of Psoralens against sUV-B (pUV-B), stimulates higher production of UV-B protective pigments (flavonoids and carotenoids) and helps in maintaining its biomass against UV-B stress. Antioxidative defense system in the test plant was activated by combined treatment of Psoralens and sUV-B as evidenced by the enhanced activity of enzymatic (ascorbate peroxidase-APX, superoxide dismutase-SOD, POX) and non-enzymatic (ascorbic acid and phenol) antioxidants. Individual treatments of Psoralens and sUV-B showed inhibitory effect on various morphological traits i.e. reduction in plant height, leaf area and ultimately on biomass production. Our results clearly indicated that adverse effect of sUV-B on biomass production was ameliorated by pre- treatment with Psoralens.

Isolation and functional characterization of CYP71AJ4 encoding for the first P450 monooxygenase of angular furanocoumarin biosynthesis

The biosynthesis of linear and angular furanocoumarins is still poorly understood at the molecular level, with only psoralen synthase (CYP71AJ1) identified from Ammi majus. Using cDNA probes inferred from CYP71AJ1, three orthologs were isolated from Apium graveolens (CYP71AJ2) and Pastinaca sativa (CYP71AJ3 and -4) and functionally expressed in yeast cells. CYP71AJ2 and CYP71AJ3 displayed psoralen synthase activity, whereas CYP71AJ4 only catalyzed the conversion of (+)-columbianetin to angelicin and negligible amounts of a hydroxylated columbianetin by-product. CYP71AJ4 thus constitutes the first fully characterized P450 monooxygenase specific for the angular furanocoumarin pathway. The angelicin synthase exhibited an apparent K(m) of 2.1 +/- 0.4 microm for (+)-columbianetin and a k(cat) of 112 +/- 14 min(-1). Moreover, the use of 3'-deuterated (+)-columbianetin as substrate led to an almost complete "metabolic switch," resulting in the synthesis of anti-3'-hydroxy-3'-deuterated(+)-columbianetin. This confirms that angelicin synthase attacks columbianetin by syn-elimination of hydrogen from C-3'. Sequence comparison between psoralen synthase (CYP71AJ3) and angelicin synthase (CYP71AJ4) showed 70% identity, whereas the identity dropped to 40% in those regions thought to provide the substrate recognition sites. Accordingly, CYP71AJ3 and CYP71AJ4 might be derived from a common ancestor of unknown functionality by gene duplication and subsequent molecular evolution.

Non-natural cinnamic acid derivatives as substrates of cinnamate 4-hydroxylase

Cinnamate 4-hydroxylase (C4H), a monooxygenase in the plant phenylpropanoid pathway, was assayed for its ability to hydroxylate 29 substrate analogues. Nine of the tested analogues with various aromatic side chains, including 3-coumaric acid, were metabolized by C4H. Seven products from these reactive analogues were characterized using LC/MS, 1H NMR and 13C NMR spectroscopic analysis. For example, caffeic acid was the product of 3-coumaric acid. The products 4-hydroxy-2-chlorocinnamic acid and 4-hydroxy-2-ethoxycinnamic acid are novel compounds that have not been previously reported. The kinetic parameters of C4H towards these analogues were determined.

Molecular cloning and functional characterization of psoralen synthase, the first committed monooxygenase of furanocoumarin biosynthesis

Ammi majus L. accumulates linear furanocoumarins by cytochrome P450 (CYP)-dependent conversion of 6-prenylumbelliferone via (+)-marmesin to psoralen. Relevant activities, i.e. psoralen synthase, are induced rapidly from negligible background levels upon elicitation of A. majus cultures with transient maxima at 9-10 h and were recovered in labile microsomes. Expressed sequence tags were cloned from elicited Ammi cells by a nested DD-RT-PCR strategy with CYP-specific primers, and full-size cDNAs were generated from those fragments correlated in abundance with the induction profile of furanocoumarin-specific activities. One of these cDNAs representing a transcript of maximal abundance at 4 h of elicitation was assigned CYP71AJ1. Functional expression in Escherichia coli or yeast cells initially failed but was accomplished eventually in yeast cells after swapping the N-terminal membrane anchor domain with that of CYP73A1. The recombinant enzyme was identified as psoralen synthase with narrow substrate specificity for (+)-marmesin. Psoralen synthase catalyzes a unique carbon-chain cleavage reaction concomitantly releasing acetone by syn-elimination. Related plants, i.e. Heracleum mantegazzianum, are known to produce both linear and angular furanocoumarins by analogous conversion of 8-prenylumbelliferone via (+)-columbianetin to angelicin, and it was suggested that angelicin synthase has evolved from psoralen synthase. However, (+)-columbianetin failed as substrate but competitively inhibited psoralen synthase activity. Analogy modeling and docked solutions defined the conditions for high affinity substrate binding and predicted the minimal requirements to accommodate (+)-columbianetin in the active site cavity. The studies suggested that several point mutations are necessary to pave the road toward angelicin synthase evolution.