Malonyl-coenzyme A:isoflavone 7-O-glucoside-6"-O-malonyltransferase from roots of chick pea (Cicer arietinum L.)

Constitutive overexpression of GsIMaT2 gene from wild soybean enhances rhizobia interaction and increase nodulation in soybean (Glycine max)

BACKGROUND

Since the root nodules formation is regulated by specific and complex interactions of legume and rhizobial genes, there are still too many questions to be answered about the role of the genes involved in the regulation of the nodulation signaling pathway.

RESULTS

The genetic and biological roles of the isoflavone-7-O-beta-glucoside 6″-O-malonyltransferase gene GsIMaT2 from wild soybean (Glycine soja) in the regulation of nodule and root growth in soybean (Glycine max) were examined in this work. The effect of overexpressing GsIMaT2 from G. soja on the soybean nodulation signaling system and strigolactone production was investigated. We discovered that the GsIMaT2 increased nodule numbers, fresh nodule weight, root weight, and root length by boosting strigolactone formation. Furthermore, we examined the isoflavone concentration of transgenic G. max hairy roots 10 and 20 days after rhizobial inoculation. Malonyldaidzin, malonylgenistin, daidzein, and glycitein levels were considerably higher in GsMaT2-OE hairy roots after 10- and 20-days of Bradyrhizobium japonicum infection compared to the control. These findings suggest that isoflavones and their biosynthetic genes play unique functions in the nodulation signaling system in G. max.

CONCLUSIONS

Finally, our results indicate the potential effects of the GsIMaT2 gene on soybean root growth and nodulation. This study provides novel insights for understanding the epistatic relationship between isoflavones, root development, and nodulation in soybean.

HIGHLIGHTS

* Cloning and Characterization of 7-O-beta-glucoside 6″-O-malonyltransferase (GsIMaT2) gene from wild soybean (G. soja). * The role of GsIMaT2 gene in the regulation of root nodule development. *Overexpression of GsMaT2 gene increases the accumulation of isoflavonoid in transgenic soybean hairy roots. * This gene could be used for metabolic engineering of useful isoflavonoid production.

Glycosidically bound aroma precursors in fruits: A comprehensive review

Fruit aroma is mainly contributed by free and glycosidically bound aroma compounds, in which glycosidically bound form can be converted into free form during storage and processing, thereby enhancing the overall aroma property. In recent years, the bound aroma precursors have been widely used as flavor additives in the food industry to enhance, balance and recover the flavor of products. This review summarizes the fruit-derived aroma glycosides in different aspects including chemical structures, enzymatic hydrolysis, biosynthesis and occurrence. Aroma glycosides structurally involve an aroma compound (aglycone) and a sugar moiety (glycone). They can be hydrolyzed to release free volatiles by endo- and/or exo-glucosidase, while their biosynthesis refers to glycosylation process using glycosyltransferases (GTs). So far, aroma glycosides have been found and studied in multiple fruits such as grapes, mangoes, lychees and so on. Additionally, their importance in flavor perception, their utilization in food flavor enhancement and other industrial applications are also discussed. Aroma glycosides can enhance flavor perception via hydrolyzation by β-glucosidase in human saliva. Moreover, they are able to impart product flavor by controlling the liberation of active volatiles in industrial applications. This review provides fundamental information for the future investigation on the fruit-derived aroma glycosides.

Formation of succinyl genistin and succinyl daidzin by Bacillus species

6''-O-Succinyl-4'-hydroxyisoflavone-7-O-beta-D-glucopyranoside (succinyl-beta-daidzin) and 6''-O-succinyl-6,4'-dihydroxyisoflavone-7-O-beta-D-glucopyranoside (succinyl-beta-genistin), 2 new isoflavone metabolites, are found in cheonggukjang or natto, traditional soy-based foods fermented with Bacillus species. Standard isoflavones including daidzin, genistin, daidzein, and genistein, and mixtures of isoflavones extracted from roasted soybeans were added to the medium growing Bacillus subtilis or B. subtilis natto and formation of succinyl-beta-daidzin and succinyl-beta-genistin were monitored by high-performance liquid chromatography (HPLC). Samples containing Bacillus with daidzin and genistin produced succinyl-beta-daidzin and succinyl-beta-genistin, respectively, while those with daidzein and genistein did not produce succinyl derivatives. Daidzin in samples with B. subtilis and B. subtilis natto decreased by 39.7% and 10.7%, respectively, for 4 h incubation while genistin decreased by 66.8% and 17.6%, respectively. Genistein decreased faster than daidzein during incubation with B. subtilis or B. subtilis natto without formation of succinyl derivatives. In the case of mixture of isoflavones, succinyl derivatives increased and beta-glucosides and aglycones of isoflavones decreased significantly for 8 h incubation (P < 0.05).

Flavonoid glucuronides and a chromone from the aquatic macrophyte Stratiotes aloides

The first phytochemical analysis of the aquatic macrophyte Stratiotes aloides afforded two new flavonoid glucuronides, luteolin 7-O-beta-D-glucopyranosiduronic acid-(1-->2)-beta-D-glucopyranoside (1) and chrysoeriol 7-O-beta-D-glucopyranosiduronic acid-(1-->2)-beta-D-glucopyranoside (2), as well as the new 2-(2-hydroxypentyl)-5-carboxy-7-methoxychromone (5) and chrysoeriol 7-O-beta-(6-O-malonyl)glucopyranoside (3), which has been assigned via NMR data for the first time. Additionally, free amino acids such as tryptophan, arginine, leucine, isoleucine, phenylalanine, and tyrosine along with choline, cis-aconitic acid, the phenolic glycoside alpha-arbutine, the chlorophyll derivative phaeophorbide a, and the flavonoid glycoside luteolin 7-O-beta-(6-O-malonyl)glucopyranoside (4) were isolated. Despite the low quantities obtained in some cases (between 50-300 microg), the structures of all compounds were unambiguously elucidated by extensive NMR and MS experiments. With a delay of 2 days compound 1 (10 and 50 microM test concentration) strongly inhibited the growth of human SH-SY5Y neuroblastoma cells in a dose-dependent manner, whereas only a moderate growth inhibition of human Patu 8902 carcinoma cells could be observed. Compounds 1 and 2 showed no activities against the bacteria Escherichia coli BW25113, Pseudomonas pudida KT2440, and Enterobacter cloacae subsp. dissolvens.

Nucleocytoplasmic-localized acyltransferases catalyze the malonylation of 7-O-glycosidic (iso)flavones in Medicago truncatula

(Iso)flavonoids are commonly accumulated as malonylated or acetylated glycoconjugates in legumes. Sequence analysis on EST database of the model legume Medicago truncatula enabled us to identify nine cDNA sequences encoding BAHD super-family enzymes that are distinct from the most of the characterized anthocyanin/flavonol acyltransferase genes in other species. Functional characterization revealed that three of these corresponding enzymes, MtMaT1, 2 and 3, specifically recognize malonyl CoA as an acyl donor and catalyze the malonylation of a range of isoflavone 7-O-glucosides in vitro. These malonyltransferase genes displayed distinct tissue-specific expression patterns and responded differentially to biotic and abiotic stresses. Consistent with gene expression, the level of the accumulated malonyl isoflavone glucoside was altered in the roots of M. truncatula grown under normal and drought-stressed conditions. Overexpression of the MtMaT1 gene in a previously engineered Arabidopsis line that accumulates genistein glycosides (Proc. Natl Acad. Sci. USA, 99, 2002:14578) led to a malonylated product. Confocal microscopy of the transiently expressed MtMaT1-GFP fusion revealed strong fluorescence in both the cytoplasm and nucleus of M. truncatula and tobacco leaf cells. A truncated MtMaT1 lacking the C-terminal polypeptide of 110 amino acid residues that include the DFGWG motif, the single conserved sequence signature of BAHD super-family members, retained considerable catalytic efficiency, but showed an altered optimum pH preference for maximum activity. Such C-terminal polypeptide deletion or deletion of the DFGWG motif alone led to improper folding of the transiently expressed GFP fusion protein in living cells, and impaired nuclear localization of the enzyme.

cDNA cloning of a BAHD acyltransferase from soybean (Glycine max): isoflavone 7-O-glucoside-6''-O-malonyltransferase

A cDNA from soybean (Glycine max (L.) Merr.), GmIF7MaT, encoding malonyl-CoA:isoflavone 7-O-glucoside-6''-O-malonyltransferase, was cloned and characterized. Soybeans produce large amounts of isoflavones, which primarily accumulate in the form of their 7-O-(6''-O-malonyl-beta-D-glucosides). The cDNA was obtained by a homology-based strategy for the cDNA cloning of some flavonoid glucoside-specific malonyltransferases of the BAHD family. The expressed gene product, GmIF7MaT, efficiently catalyzed specific malonyl transfer reactions from malonyl-CoA to isoflavone 7-O-beta-D-glucosides yielding the corresponding isoflavone 7-O-(6''-O-malonyl-beta-D-glucosides) (IF7MaT activity). The k(cat) values of GmIF7MaT were much greater than those of other flavonoid glucoside-specific malonyltransferases with their preferred substrates, while the K(m) values were at comparable levels. GmIF7MaT was expressed in the roots of G. max seedlings more abundantly than in hypocotyl and cotyledon. Native IF7MaT activity was also observed in the roots, suggesting that GmIF7MaT is involved in the biosynthesis from isoflavone 7-O-beta-D-glucosides to the corresponding isoflavone 7-O-(6''-O-malonyl-beta-D-glucosides) in G. max. This protein is a member of flavonoid glucoside-specific acyltransferases in the BAHD family.

Biosynthesis of malonylated flavonoid glycosides on the basis of malonyltransferase activity in the petals of Clitoria ternatea

The crude malonyltransferase from the petals of Clitoria ternatea was characterized enzymatically to investigate its role on the biosynthetic pathways of anthocyanins and flavonol glycosides. In C. ternatea, a blue flower cultivars (DB) and mauve flower variety (WM) accumulate polyacylated anthocyanins (ternatins) and delphinidin 3-O-(6''-O-malonyl)-beta-glucoside which is one of the precursors of ternatins, respectively. Moreover, WM accumulates minor delphinidin glycosides - 3-O-beta-glucoside, 3-O-(2''-O-alpha-rhamnosyl)-beta-glucoside, 3-O-(2''-O-alpha-rhamnosyl-6''-O-malonyl)-beta-glucoside of delphinidin. These glycosidic patterns for minor anthocyanins in WM are also found among the minor flavonol glycosides in all the varieties including a white flower variety (WW) although the major flavonol glycosides are 3-O-(2''-O-alpha-rhamnosyl)-beta-glucoside, 3-O-(6''-O-alpha-rhamnosyl)-beta-glucoside, 3-O-(2'',6''-di-O-alpha-rhamnosyl)-beta-glucoside of kaempferol, quercetin, and myricetin. How do the enzymatic characteristics affect the variety of glycosidic patterns in the flavonoid glycoside biosynthesis among these varieties? While the enzyme from DB highly preferred delphinidin 3-O-beta-glucoside in the presence of malonyl-CoA, it also has a preference for other anthocyanidin 3-O-beta-glucosides. It could use flavonol 3-O-beta-glucosides in much lower specific activities than anthocyanins; however, it could not utilize 3-O-(2''-O-alpha-rhamnosyl)-beta-glucosides of anthocyanins and flavonols, and 3,3'-di- and 3,3',5'-tri-O-beta-glucoside of delphinidin - other possible precursors in ternatins biosynthesis. It highly preferred malonyl-CoA as an acyl donor in the presence of delphinidin 3-O-beta-glucoside. The crude enzymes prepared from WM and WW had the same enzymatic characteristics. These results suggested that 3-O-(2''-O-alpha-rhamnosyl-6''-O-malonyl)-beta-glucosides of flavonoids were synthesized via 3-O-(6''-O-malonyl)-beta-glucosides rather than via 3-O-(2''-O-alpha-rhamnosyl)-beta-glucosides, and that malonylation proceeded prior to glucosylation at the B-ring of delphinidin in the early biosynthetic steps towards ternatins. It seemed that the substrate specificities largely affected the difference in the accumulated amount of malonylated glycosides between anthocyanins and flavonols although they are not simply proportional to the accumulation ratio. This enzyme might join in the production of both malonylanthocyanins and flavonol malonylglycosides as a result of broad substrate specificities towards flavonoid 3-O-beta-glucosides.

Phytoestrogens

Collectively, plants contain several different families of natural products among which are compounds with weak estrogenic or antiestrogenic activity toward mammals. These compounds, termed phytoestrogens, include certain isoflavonoids, flavonoids, stilbenes, and lignans. The best-studied dietary phytoestrogens are the soy isoflavones and the flaxseed lignans. Their perceived health beneficial properties extend beyond hormone-dependent breast and prostate cancers and osteoporosis to include cognitive function, cardiovascular disease, immunity and inflammation, and reproduction and fertility. In the future, metabolic engineering of plants could generate novel and exquisitely controlled dietary sources with which to better assess the potential health beneficial effects of phytoestrogens.

3,4-Dichloroaniline is detoxified and exported via different pathways in Arabidopsis and soybean

The metabolic fate of [UL-14C]-3,4-dichloroaniline (DCA) was investigated in Arabidopsis root cultures and soybean plants over a 48 h period following treatment via the root media. DCA was rapidly taken up by both species and metabolised, predominantly to N-malonyl-DCA in soybean and N-glucosyl-DCA in Arabidopsis. Synthesis occurred in the roots and the respective conjugates were largely exported into the culture medium, a smaller proportion being retained within the plant tissue. Once conjugated, the DCA metabolites in the medium were not then readily taken up by roots of either species. The difference in the routes of DCA detoxification in the two plants could be explained partly by the relative activities of the respective conjugating enzymes, soybean containing high DCA-N-malonyltransferase activity, while in Arabidopsis DCA-N-glucosyltransferase activity predominated. A pre-treatment of plants with DCA increased DCA-N-malonyltransferase activity in soybean but not in Arabidopsis, indicating differential regulation of this enzyme in the two plant species. This study demonstrates that DCA can undergo two distinct detoxification mechanisms which both lead to the export of conjugated metabolites from roots into the surrounding medium in contrast to the vacuolar deposition more commonly associated with the metabolism of xenobiotics in plants.

Elicitor-induced changes in isoflavonoid metabolism in red clover roots

When roots of 5-d-old red clover (Trifolium pratense L.) seedlings were treated with chitohexaose and CuCl(2), constitutive glucosidic conjugates of formononetin (F) and (-)-maackiain (Ma) promptly disappeared. Free F and Ma, which were not detected in the control tissues, rapidly appeared to reach the maximum levels 24 h after the initiation of treatment and then declined. The pattern of appearance and disappearance was the same between the tissues treated with chitohexaose and CuCl(2). The enzyme activities related to isoflavonoid metabolism were investigated using crude extracts from elicitor-treated roots. The conjugate-forming glucosyltransferase and malonyltransferase activities were lost or markedly reduced after elicitor treatment. On the other hand, malonylesterase and glucosidase activities remained unchanged or showed only slight increase. Phenylalanine ammonia-lyase activity disappeared following elicitor treatment. These results indicated that free aglycones were produced from the conjugate pool by hydrolysis under conditions in which the biosynthetic pathway was extinguished. The amount of Ma produced did not explain that of MaGM lost (about 45%). Since Ma, but not its conjugates, served as a substrate for peroxidase from the elicitor-treated roots, Ma was considered to be converted to insoluble materials.

Anthocyanin 5-aromatic acyltransferase from Gentiana triflora. Purification, characterization and its role in anthocyanin biosynthesis

Acylation with hydroxycinnamic acids stabilizes anthocyanins and makes their colour bluer (bathochromic shift). We purified to homogeneity one acylation enzyme, hydroxycinnamoyl-CoA:anthocyanidin 3,5-diglucoside 5-O-glucoside-6"'-O-hydroxycinnamoyltransferase, from blue petals of Gentiana triflora. It is a single polypeptide protein of 52 kDa with a pI of 4.6. It catalyzes the transfer of the p-coumaric acid and caffeic acid from their CoA esters to the 5-glucosyl moiety of anthocyanidin 3,5-diglucosides but could not use malonyl-CoA as an acyl donor. Neither anthocyanidin 3-monoglucoside nor anthocyanins aromatically acylated at the 3-glucosyl moiety could be acylated by this enzyme. Aromatic acylation of anthocyanidin 3,5-diglucoside by this enzyme caused a bathochromic shift and increased pigment stability in neutral to weakly basic pH. Other anthocyanins from the petals of G. triflora were isolated and their structures were determined by fast-atom-bombardment MS and NMR. The biosynthetic pathway of gentiodelphin, a diacylated anthocyanin accumulating in G. triflora petals, is proposed on the basis of these results.

Plant biochemistry of xenobiotics: isolation and properties of soybean O- and N-glucosyl and O- and N-malonyltransferases for chlorinated phenols and anilines

O-Glucosyltransferase (O-GT), O-malonyltransferase (O-MAT), N-glucosyltransferase (N-GT), and N-malonyltransferase (N-MAT) activities have been detected in cultured soybean cells, using pentachlorophenol and 3,4-dichloroaniline as xenobiotic standard substrates. The O-GT was purified approximately 1000-fold, and the N-MAT approximately 70-fold. There was an extensive copurification of O-GT and O-MAT. The following functional molecular weight values were obtained, 47 kDA (O-GT), 48 kDA (O-MAT) 43 kDa (N-GT), and 48 kDa (N-MAT). O-GT and N-MAT appeared to be monomeric polypeptides with isoelectric points of approximately 4.8 and approximately 6.1, respectively. The O-GT, N-GT, and N-MAT activities had marked substrate specificities for chlorinated aromatic xenobiotics and thus illustrate the existence of plant isoenzymes with specificity for xenobiotics.

Purfication and properties of a specific isoflavone 7-O-glucoside-6''-malonate malonyestrase from roots of chickpea (Cicer arietinum L.)

Protein extracts from roots of chickpea (Cicer arietinum L.) plants contained high esterase activity hydrolyzing malonate hemiesters of isoflavone 7-O-glucosides. Using 5,7-dihydroxy-4'-methoxyisoflavone (biochanin A) 7-O-glucoside-6"-malonate as a substrate, a specific malonylesterase was purified about 700-fold to near homogeneity. The purified enzyme possesses an extremely low enzyme activity with synthetic esterase substrates. Various putative nonspecific esterases, as tested with alpha-naphthylacetate, were removed during enzyme purification. The malonylesterase demonstrated a very high molecular mass in gel chromatography and in sedimentation analyses with sucrose gradients (greater than or equal to 2 X 10(6)). Analytical sodium dodecyl sulfate-polyacrylamide gel electrophoresis pointed to a single subunit of 32,000. The catalyzed reaction showed a pH optimum at 7.5 and a temperature optimum between 30 and 35 degrees C. The apparent Km for biochanin A 7-O-glucoside-6"-malonate was (4.2 +/- 1.2) X 10(-4) M. The malonylesterase was insensitive to the esterase inhibitors eserine and neostigmine (10(-3) M) as well as phenylmethylsulfonyl fluoride, paraoxon, and diisopropylfluorophosphate (10(-4) M). On the other hand enzyme activity was totally inhibited by Hg2+ ions (10(-5) M) and p-hydroxymercuribenzoate (10(-4) M), whereas iodoacetamide (10(-6)-10(-4) M) inhibited only partially. Di- and tricarboxylic acids strongly stimulated enzyme activity at 10(-2) M. These properties indicate that the malonylesterase from chickpea roots greatly differs from other known esterases. The possible biological function of the specific malonylesterase is discussed in relation to isoflavone conjugate metabolism in chickpea.

Efficient uptake of flavonoids into parsley (Petroselinum hortense) vacuoles requires acylated glycosides

Vacuoles were prepared from cultured parsley cells by polyamine-induced rupture of protoplasts. Acid-phosphatase activity, associated exclusively with the vacuoles, served for determination of vacuole yield in subsequent transport studies. Isolated vacuoles rapidly accumulated [2‴-(14)C]apigenin 7-O-(6-O-malonylglucoside) or 2″-(14)C]β-methyl D-6-O-malonylglucoside added at approximately 20 nM and 1.5 μM concentration, respectively, to the incubation mixture. The accumulation was linear with time and strongly dependent on alkaline buffer conditions as well as on the age of the vacuole preparation. Subsequent addition of a malonic hemiester esterase did not relase the label from the vacuoles. Moreover, neither [2-(14)C]apigenin 7-O-glucoside or [2-(14)C]malonic acid accumulated in the vacuoles under any assay conditions, nor did such compounds or β-methyl D-glucopyranoside, a malonic diester, and a succinic monoester inhibit transport of the acylated flavonoid. Transport was, however, inhibited by β-methyl D-6-O-malonylglucopyranoside. Vacuoles which had been incubated for more than 40 min at pH 8.0 did not stain any more with neutral-red dye and concomitantly lost the previously accumulated acylated glucoside. Our data confirm that malonylglucoside uptake by parsley vacuoles involves selective transport sites. It is suggested that changes in the molecular symmetry of the malonylglucosides are responsible for vacuolar trapping of flavonoids in parsley.