Characterization of leachianone G 2"-dimethylallyltransferase, a novel prenyl side-chain elongation enzyme for the formation of the lavandulyl group of sophoraflavanone G in Sophora flavescens Ait. cell suspension cultures

The Protective Effect of Sanggenol L Against DMBA-induced Hamster Buccal Pouch Carcinogenesis Induces Apoptosis and Inhibits Cell Proliferative Signalling Pathway

BACKGROUND

Oral squamous cell carcinoma (OSCC) has a poor prognosis when treated with surgery and chemotherapy. Therefore, a new therapy and preventative strategy for OSCC and its underlying mechanisms are desperately needed. The purpose of this study was to examine the chemopreventive effects of sanggenol L on oral squamous cell carcinoma (OSCC). The research focused on molecular signalling pathways in 7,12-dimethylbenz(a)anthracene (DMBA)-induced hamster buccal pouch (HBP) carcinogenesis.

AIM

The purpose of this study was to look at the biochemical and chemopreventive effects of sanggenol L on 7,12-dimethylbenz(a)anthracene (DMBA)-induced HBP (hamster buccal pouch) carcinogenesis via cell proliferation and the apoptotic pathway.

METHODS

After developing squamous cell carcinoma, oral tumours continued to progress leftward into the pouch 3 times per week for 10 weeks while being exposed to 0.5 % reactive DMBA three times per week. Tumour growth was caused by biochemical abnormalities that induced inflammation, increased cell proliferation, and decreased apoptosis.

RESULTS

Oral sanggenol L (10 mg/kg bw) supplementation with cancer-induced model DMBApainted hamsters prevented tumour occurrences, improved biochemistry, inhibited inflammatory markers, decreased cell proliferation marker expression of tumour necrosis factor-alpha (TNF- α), nuclear factor (NF-κB), cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), and induced apoptosis.

CONCLUSION

Sanggenol L could be developed into a new medicine for the treatment of oral carcinogenesis.

Heterologous biosynthesis of isobavachalcone in tobacco based on in planta screening of prenyltransferases

Isobavachalcone (IBC) is a prenylated chalcone mainly distributed in some Fabaceae and Moraceae species. IBC exhibits a wide range of pharmacological properties, including anti-bacterial, anti-viral, anti-inflammatory, and anti-cancer activities. In this study, we attempted to construct the heterologous biosynthesis pathway of IBC in tobacco (Nicotiana tabacum). Four previously reported prenyltransferases, including GuILDT from Glycyrrhiza uralensis, HlPT1 from Humulus lupulus, and SfILDT and SfFPT from Sophora flavescens, were subjected to an in planta screening to verify their activities for the biosynthesis of IBC, by using tobacco transient expression with exogenous isoliquiritigenin as the substrate. Only SfFPT and HlPT1 could convert isoliquiritigenin to IBC, and the activity of SfFPT was higher than that of HlPT1. By co-expression of GmCHS8 and GmCHR5 from Glycine max, endogenous isoliquiritigenin was generated in tobacco leaves (21.0 μg/g dry weight). After transformation with a multigene vector carrying GmCHS8, GmCHR5, and SfFPT, de novo biosynthesis of IBC was achieved in transgenic tobacco T₀ lines, in which the highest amount of IBC was 0.56 μg/g dry weight. The yield of IBC in transgenic plants was nearly equal to that in SfFPT transient expression experiments, in which substrate supplement was sufficient, indicating that low IBC yield was not attributed to the substrate supplement. Our research provided a prospect to produce valuable prenylflavonoids using plant-based metabolic engineering.

Synthetic production of prenylated naringenins in yeast using promiscuous microbial prenyltransferases

Reconstitution of prenylflavonoids using the flavonoid biosynthetic pathway and prenyltransferases (PTs) in microbes can be a promising attractive alternative to plant-based production or chemical synthesis. Here, we demonstrate that promiscuous microbial PTs can be a substitute for regiospecific but mostly unidentified botanical PTs. To test the prenylations of naringenin, we constructed a yeast strain capable of producing naringenin from l-phenylalanine by genomic integration of six exogenous genes encoding components of the naringenin biosynthetic pathway. Using this platform strain, various microbial PTs were tested for prenylnaringenin production. In vitro screening demonstrated that the fungal AnaPT (a member of the tryptophan dimethylallyltransferase family) specifically catalyzed C-3′ prenylation of naringenin, whereas SfN8DT-1, a botanical PT, specifically catalyzed C-8 prenylation. In vivo, the naringenin-producing strain expressing the microbial AnaPT exhibited heterologous microbial production of 3′-prenylnaringenin (3′-PN), in contrast to the previously reported in vivo production of 8-prenylnaringenin (8-PN) using the botanical SfN8DT-1. These findings provide strategies towards expanding the production of a variety of prenylated compounds, including well-known prenylnaringenins and novel prenylflavonoids. These results also suggest the opportunity for substituting botanical PTs, both known and unidentified, that display relatively strict regiospecificity of the prenyl group transfer.

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Promiscuous microbial prenyltransferases replaced regiospecific botanical enzymes.

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A stable yeast strain that produced naringenin from l-phenylalanine was constructed.

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A fungal prenyltransferase (AnaPT) catalyzed C-3′ prenylation of naringenin.

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AnaPT catalyzed the first microbial production of 3′-prenylnaringenin.

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Microbial prenyltransferases permit the production of various prenylated compounds.

LaPT2 Gene Encodes a Flavonoid Prenyltransferase in White Lupin

Legume plants are rich in prenylated flavonoid compounds, which play an important role in plant defense and human health. In the present study, we identified a prenyltransferase (PT) gene, named LaPT2, in white lupin (Lupinus albus), which shows a high identity and close relationship with the other known PT genes involved in flavonoid prenylation in planta. The recombinant LaPT2 protein expressed in yeast cells exhibited a relatively strong activity toward several flavonols (e.g., kaempferol, quercetin, and myricetin) and a relatively weak activity toward flavanone (naringenin). In addition, the recombinant LaPT2 protein was also active toward several other types of flavonoids, including galangin, morin, 5-deoxyquercetin, 4'-O-methylkaempferol, taxifolin, and aromadendrin, with distinct enzymatic affinities. The LaPT2 gene was preferentially expressed in the roots, which is consistent with the presence of prenylated flavonoid kaempferol in the roots. Moreover, we found that the expression level of LaPT2 paralleled with those of LaF3H1 and LaFLS2 genes that were relatively higher in roots and lower in leaves, suggesting that they were essential for the accumulation of prenylated flavonoid kaempferol in roots. The deduced full-length LaPT2 protein and its signal peptide fused with a green fluorescent protein (GFP) are targeted to plastids in the Arabidopsis thaliana protoplast. Our study demonstrated that LaPT2 from white lupin is responsible for the biosynthesis of prenylated flavonoids, in particular flavonols, which could be utilized as phytoalexin for plant defense and bioactive flavonoid compounds for human health.

The different tolerance to magnesium deficiency of two grapevine rootstocks relies on the ability to cope with oxidative stress

BACKGROUND

Magnesium (Mg) deficiency causes physiological and molecular responses, already dissected in several plant species. The study of these responses among genotypes showing a different tolerance to the Mg shortage can allow identifying the mechanisms underlying the resistance to this nutritional disorder. To this aim, we compared the physiological and molecular responses (e.g. changes in root metabolome and transcriptome) of two grapevine rootstocks exhibiting, in field, different behaviors with respect to Mg shortage (1103P, tolerant and SO4 susceptible).

RESULTS

The two grapevine rootstocks confirmed, in a controlled growing system, their behavior in relation to the tolerance to Mg deficiency. Differences in metabolite and transcriptional profiles between the roots of the two genotypes were mainly linked to antioxidative compounds and the cell wall constituents. In addition, differences in secondary metabolism, in term of both metabolites (e.g. alkaloids, terpenoids and phenylpropanoids) and transcripts, assessed between 1103P and SO4 suggest a different behavior in relation to stress responses particularly at early stages of Mg deficiency.

CONCLUSIONS

Our results suggested that the higher ability of 1103P to tolerate Mg shortage is mainly linked to its capability of coping, faster and more efficiently, with the oxidative stress condition caused by the nutritional disorder.

Molecular evolution of parsnip (Pastinaca sativa) membrane-bound prenyltransferases for linear and/or angular furanocoumarin biosynthesis

In Apiaceae, furanocoumarins (FCs) are plant defence compounds that are present as linear or angular isomers. Angular isomers appeared during plant evolution as a protective response to herbivores that are resistant to linear molecules. Isomeric biosynthesis occurs through prenylation at the C6 or C8 position of umbelliferone. Here, we report cloning and functional characterization of two different prenyltransferases, Pastinaca sativa prenyltransferase 1 and 2 (PsPT1 and PsPT2), that are involved in these crucial reactions. Both enzymes are targeted to plastids and synthesize osthenol and demethylsuberosin (DMS) using exclusively umbelliferone and dimethylallylpyrophosphate (DMAPP) as substrates. Enzymatic characterization using heterologously expressed proteins demonstrated that PsPT1 is specialized for the synthesis of the linear form, demethylsuberosin, whereas PsPT2 more efficiently catalyses the synthesis of its angular counterpart, osthenol. These results are the first example of a complementary prenyltransferase pair from a single plant species that is involved in synthesizing defensive compounds. This study also provides a better understanding of the molecular mechanisms governing the angular FC biosynthetic pathway in apiaceous plants, which involves two paralogous enzymes that share the same phylogenetic origin.

Antimicrobial action of an endophytic fungi from Sophor flavescens and structure identification of its active constituent

Endophytic fungus BS002 was isolated and characterized from Sophora flavescens by plate method, which has broad antimicrobial activity. Isolation and trace of a new bioactive compound from the fungus' culture extracts with the method of column chromatography and TLC biological autoradiography was conducted. Finally, it was identified as 6,7-(2'E) dibutenyl-5,8-dihydroxy-(Z)-cyclooct-2-ene-1,4-dione by nuclear magnetic resonance, infrared and liquid chromatography-mass spectrometry. The compound presented strong antifungal activities for example: Botryosphaeria berengriana f.sp. piricola, Physalospora piricola, Cladosporium cucumerinum Ell. Arthur., Fusarium oxysporum f.sp. cucumerinum, Fusarium moniliforme. The inhibition to Physalospora piricola was the strongest with an antibacterial diameter of 45 mm. This paper is the first report of the antimicrobial activity of endophytic fungi BS002 that was the secondary metabolites extracted from the seeds of Sophora flavescens. The results provide a broad foreground for biopharmaceuticals and biopesticide.

The biosynthetic origin of irregular monoterpenes in Lavandula: isolation and biochemical characterization of a novel cis-prenyl diphosphate synthase gene, lavandulyl diphosphate synthase

Lavender essential oils are constituted predominantly of regular monoterpenes, for example linalool, 1,8-cineole, and camphor. However, they also contain irregular monoterpenes including lavandulol and lavandulyl acetate. Although the majority of genes responsible for the production of regular monoterpenes in lavenders are now known, enzymes (including lavandulyl diphosphate synthase (LPPS)) catalyzing the biosynthesis of irregular monoterpenes in these plants have not been described. Here, we report the isolation and functional characterization of a novel cis-prenyl diphosphate synthase cDNA, termed Lavandula x intermedia lavandulyl diphosphate synthase (LiLPPS), through a homology-based cloning strategy. The LiLPPS ORF, encoding for a 305-amino acid long protein, was expressed in Escherichia coli, and the recombinant protein was purified by nickel-nitrilotriacetic acid affinity chromatography. The approximately 34.5-kDa bacterially produced protein specifically catalyzed the head-to-middle condensation of two dimethylallyl diphosphate units to LPP in vitro with apparent Km and kcat values of 208 ± 12 μm and 0.1 s(-1), respectively. LiLPPS is a homodimeric enzyme with a sigmoidal saturation curve and Hill coefficient of 2.7, suggesting a positive co-operative interaction among its catalytic sites. LiLPPS could be used to modulate the production of lavandulol and its derivatives in plants through metabolic engineering.

Metabolic engineering for the production of prenylated polyphenols in transgenic legume plants using bacterial and plant prenyltransferases

Prenylated polyphenols are secondary metabolites beneficial for human health because of their various biological activities. Metabolic engineering was performed using Streptomyces and Sophora flavescens prenyltransferase genes to produce prenylated polyphenols in transgenic legume plants. Three Streptomyces genes, NphB, SCO7190, and NovQ, whose gene products have broad substrate specificity, were overexpressed in a model legume, Lotus japonicus, in the cytosol, plastids or mitochondria with modification to induce the protein localization. Two plant genes, N8DT and G6DT, from Sophora flavescens whose gene products show narrow substrate specificity were also overexpressed in Lotus japonicus. Prenylated polyphenols were undetectable in these plants; however, supplementation of a flavonoid substrate resulted in the production of prenylated polyphenols such as 7-O-geranylgenistein, 6-dimethylallylnaringenin, 6-dimethylallylgenistein, 8-dimethylallynaringenin, and 6-dimethylallylgenistein in transgenic plants. Although transformants with the native NovQ did not produce prenylated polyphenols, modification of its codon usage led to the production of 6-dimethylallylnaringenin and 6-dimethylallylgenistein in transformants following naringenin supplementation. Prenylated polyphenols were not produced in mitochondrial-targeted transformants even under substrate feeding. SCO7190 was also expressed in soybean, and dimethylallylapigenin and dimethylallyldaidzein were produced by supplementing naringenin. This study demonstrated the potential for the production of novel prenylated polyphenols in transgenic plants. In particular, the enzymatic properties of prenyltransferases seemed to be altered in transgenic plants in a host species-dependent manner.

Production of prenylated flavonoids in tomato fruits expressing a prenyltransferase gene from Streptomyces coelicolor A3(2)

Flavonoids are natural compounds found in many plants, including the important fruit crop, tomato. Prenylated flavonoids consist of a large group of compounds, which often exhibit antitumour, antibacterial and/or anti-androgen activities. In this study, we engineered the biosynthesis of prenylated flavonoids using a Streptomyces prenyltransferase HypSc (SCO7190) possessing broad-range substrate specificity, in tomato as a host plant. LC/MS/MS analysis demonstrated the generation of 3'-dimethylallyl naringenin in tomato fruits when recombinant HypSc protein was targeted to the plastids, whereas the recombinant protein hardly produced this compound in vitro. This is the first report confirming the accumulation of a prenylated flavonoid using a bacterial prenyltransferase in transgenic plants, and our results suggest that the product specificities of prenyltransferases can be significantly influenced by the host plant.

Functional characterization of LePGT1, a membrane-bound prenyltransferase involved in the geranylation of p-hydroxybenzoic acid

The AS-PT (aromatic substrate prenyltransferase) family plays a critical role in the biosynthesis of important quinone compounds such as ubiquinone and plastoquinone, although biochemical characterizations of AS-PTs have rarely been carried out because most members are membrane-bound enzymes with multiple transmembrane alpha-helices. PPTs [PHB (p-hydroxybenzoic acid) prenyltransferases] are a large subfamily of AS-PTs involved in ubiquinone and naphthoquinone biosynthesis. LePGT1 [Lithospermum erythrorhizon PHB geranyltransferase] is the regulatory enzyme for the biosynthesis of shikonin, a naphthoquinone pigment, and was utilized in the present study as a representative of membrane-type AS-PTs to clarify the function of this enzyme family at the molecular level. Site-directed mutagenesis of LePGT1 with a yeast expression system indicated three out of six conserved aspartate residues to be critical to the enzymatic activity. A detailed kinetic analysis of mutant enzymes revealed the amino acid residues responsible for substrate binding were also identified. Contrary to ubiquinone biosynthetic PPTs, such as UBIA in Escherichia coli which accepts many prenyl substrates of different chain lengths, LePGT1 can utilize only geranyl diphosphate as its prenyl substrate. Thus the substrate specificity was analysed using chimeric enzymes derived from LePGT1 and UBIA. In vitro and in vivo analyses of the chimeras suggested that the determinant region for this specificity was within 130 amino acids of the N-terminal. A 3D (three-dimensional) molecular model of the substrate-binding site consistent with these biochemical findings was generated.

Cloning and characterization of naringenin 8-prenyltransferase, a flavonoid-specific prenyltransferase of Sophora flavescens

Prenylated flavonoids are natural compounds that often represent the active components in various medicinal plants and exhibit beneficial effects on human health. Prenylated flavonoids are hybrid products composed of a flavonoid core mainly attached to either 5-carbon (dimethylallyl) or 10-carbon (geranyl) prenyl groups derived from isoprenoid (terpenoid) metabolism, and the prenyl groups are crucial for their biological activity. Prenylation reactions in vivo are crucial coupling processes of two major metabolic pathways, the shikimate-acetate and isoprenoid pathways, in which these reactions are also known as a rate-limiting step. However, none of the genes responsible for the prenylation of flavonoids has been identified despite more than 30 years of research in this field. We have isolated a prenyltransferase gene from Sophora flavescens, SfN8DT-1, responsible for the prenylation of the flavonoid naringenin at the 8-position, which is specific for flavanones and dimethylallyl diphosphate as substrates. Phylogenetic analysis shows that SfN8DT-1 has the same evolutionary origin as prenyltransferases for vitamin E and plastoquinone. The gene expression of SfN8DT-1 is strictly limited to the root bark where prenylated flavonoids are solely accumulated in planta. The ectopic expression of SfN8DT-1 in Arabidopsis thaliana resulted in the formation of prenylated apigenin, quercetin, and kaempferol, as well as 8-prenylnaringenin. SfN8DT-1 represents the first flavonoid-specific prenyltransferase identified in plants and paves the way for the identification and characterization of further genes responsible for the production of this large and important class of secondary metabolites.

Biogenesis, molecular regulation and function of plant isoprenoids

Isoprenoids represent the oldest class of known low molecular-mass natural products synthesized by plants. Their biogenesis in plastids, mitochondria and the endoplasmic reticulum-cytosol proceed invariably from the C5 building blocks, isopentenyl diphosphate and/or dimethylallyl diphosphate according to complex and reiterated mechanisms. Compounds derived from the pathway exhibit a diverse spectrum of biological functions. This review centers on advances obtained in the field based on combined use of biochemical, molecular biology and genetic approaches. The function and evolutionary implications of this metabolism are discussed in relation with seminal informations gathered from distantly but related organisms.

Transporters of secondary metabolites

The membrane transport of plant secondary metabolites is a newly developing research area. Recent progress in genome and expressed sequence tag (EST) databases has revealed that many transporters and channels exist in plant genome. Studies of the genetic sequences that encode these proteins, and of phenotypes caused by the mutation of these sequences, have been used to characterize the membrane transport of plant secondary metabolites. Such studies have clarified that membrane transport is fairly specific and highly regulated for each secondary metabolite. Not only genes that are involved in the biosynthesis of secondary metabolites but also genes that are involved in their transport will be important for systematic metabolic engineering aimed at increasing the productivity of valuable secondary metabolites in planta.