Identification of a Flavin Monooxygenase-Like Flavonoid 8-Hydroxylase with Gossypetin Synthase Activity from Lotus japonicus.

Lotus japonicus is a model legume that accumulates 8-hydroxyflavonol derivatives, such as gossypetin (8-hydroxyquercetin) 3-O-glycoside, which confer the yellow color to its petals. An enzyme, flavonoid 8-hydroxylase (F8H; LjF8H), is assumed to be involved in the biosynthesis, but the specific gene is yet to be identified. The LjF8H cDNA was isolated as a flavin adenine dinucleotide (FAD)-binding monooxygenase-like protein using flower buds and flower-specific EST data of L. japonicus. LjF8H is a single copy gene on chromosome III consisting of six exons. The conserved FAD- and NAD(P)H-dependent oxidase motifs were found in LjF8H. Phylogenetic analysis suggested that LjF8H is a member of the flavin monooxygenase group but distinctly different from other known flavonoid oxygenases. Analysis of recombinant yeast microsome expressing LjF8H revealed that the enzyme catalyzed the 8-hydroxylation of quercetin. Other flavonoids, such as naringenin, eriodictyol, apigenin, luteolin, taxifolin and kaempferol, also acted as substrates of LjF8H. This broad substrate acceptance was unlike known F8Hs in other plants. Interestingly, flavanone and flavanonol, which have saturated C-C bond at positions 2 and 3 of the flavonoid C-ring, produced 6-hyroxylflavonoids as a by-product of the enzymatic reaction. Furthermore, LjF8H only accepted the 2S-isomer of naringenin, suggesting that the conformational state of the substrates might affect product specificity. The overexpression of LjF8H in Arabidopsis thaliana and Petunia hybrida synthesized gossypetin and 8-hydroxykaempferol, respectively, indicating that LjF8H was functional in plant cells. In conclusion, this study represents the first instance of cloning and identification of F8Hs responsible for gossypetin biosynthesis.

Determination of Absolute Purities of Hygroscopic Substances by Quantitative NMR Analysis for the Standardization of Quantitative Reagents in the Japanese Pharmacopoeia (Part 2).

As a new absolute quantitation method for low-molecular compounds, quantitative NMR (qNMR) has emerged. In the Japanese Pharmacopoeia (JP), 15 compounds evaluated by qNMR are listed as reagents used as the HPLC reference standards in the assay of crude drug section of the JP. In a previous study, we revealed that humidity affects purity values of hygroscopic reagents and that (i) humidity control before and during weighing is important for a reproducible preparation and (ii) indication of the absolute amount (not purity value), which is not affected by water content, is important for hygroscopic products determined by qNMR. In this study, typical and optimal conditions that affect the determination of the purity of ginsenoside Rb1 (GRB1), saikosaponin a (SSA), and barbaloin (BB) (i.e., hygroscopic reagents) by qNMR were examined. First, the effect of humidity before and during weighing on the purity of commercial GRB1, with a purity value determined by qNMR, was examined. The results showed the importance afore-mentioned. The results of SSA, which is relatively unstable in the dissolved state, suggested that the standardization of humidity control before and during weighing for a specific time provides a practical approach for hygroscopic products. In regard to BB, its humidity control for a specific time, only before weighing, is enough for a reproducible purity determination.

[Quantitative Determination Method of Aconitum Monoester Alkaloids Using Relative Molar Sensitivity (RMS) for the Assay in the Japanese Pharmacopoeia].

Recently, a novel quantitative method using relative molar sensitivity (RMS) was applied to quantify the ingredients of drugs and foods. An important development in this regard can be observed in the Japanese Pharmacopoeia (JP) 18, where the quantification of perillaldehyde, an unstable compound, in crude drug "Perilla Herb," was revised to incorporate the RMS method. In this study, the primary objective was to improve the tester safety and reduce the amount of reagents used in the JP test. To achieve this, the quantification of three toxic Aconitum monoester alkaloids (AMAs) was explored using the RMS method, employing a single reference compound for all three targets. These AMAs, namely benzoylmesaconine hydrochloride, benzoylhypaconine hydrochloride, and 14-anisoylaconine hydrochloride, which are the quantitative compounds of Kampo extracts containing Aconite Root (AR), were quantified using the reference compound benzoic acid (BA). Reliable RMS values were obtained using both 1H-quantitative NMR and HPLC/UV. Using the RMS of three AMAs relative to the BA, the AMA content (%) in commercial AMAs quantitative reagents were determined without analytical standards. Moreover, the quantitative values of AMAs using the RMS method and the calibration curve method using the three analytical standards were similar. Additionally, similar values were achieved for the three AMAs in the Kampo extracts containing AR using the RMS and the modified JP18 calibration curve methods. These results suggest that the RMS method is suitable for quantitative assays of the Kampo extracts containing AR and can serve as an alternative to the current method specified in the JP18.

The soybean F3'H protein is localized to the tonoplast in the seed coat hilum.

We previously isolated a soybean (Glycine max (L.) Merr.) flavonoid 3'-hydroxylase (F3'H) gene (sf3'h1) corresponding to the T locus, which controls pubescence and seed coat color, from two near-isogenic lines (NILs), To7B (TT) and To7G (tt). The T allele is also associated with chilling tolerance. Here, Western-blot analysis shows that the sf3'h1 protein was predominantly detected in the hilum and funiculus of the immature seed coat in To7B, whereas sf3'h1 was not detected in To7G. A truncated sf3'h1 protein isolated from To7G was detected only upon enrichment by immunoprecipitation. An analysis using diphenylboric acid 2-aminoethyl ester (DBPA) staining revealed that flavonoids accumulated in the hilum and the funiculus in both To7B and To7G. Further, the scavenging activity of the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical in methanol extracts from the funiculus and hilum of To7B was higher than that of To7G. Moreover, the enzymatic activity of F3'H was detected using microsomal fractions from yeast transformed with sf3'h1 from To7B, but not from To7G. These results indicate that sf3'h1 is involved in flavonoid biosynthesis in the seed coat and affects the antioxidant properties of those tissues. As shown by immunofluorescence microscopy, the sf3'h1 protein was detected primarily around the vacuole in the parenchymatic cells of the hilum in To7B. Further immunoelectron microscopy detected sf3'h1 protein on the membranous structure of the vacuole. Based on these observations, we conclude that F3'H, which is a cytochrome P450 monooxygenase and has been found to be localized to the ER in other plant systems, is localized in the tonoplast in soybean.

Quercetin 3,5,7,3',4'-pentamethyl ether from Kaempferia parviflora directly and effectively activates human SIRT1.

Sirtuin 1 (SIRT1), an NAD+-dependent deacetylase, is a crucial regulator that produces multiple physiological benefits, such as the prevention of cancer and age-related diseases. SIRT1 is activated by sirtuin-activating compounds (STACs). Here, we report that quercetin 3,5,7,3',4'-pentamethyl ether (KPMF-8), a natural STAC from Thai black ginger Kaempferia parviflora, interacts with SIRT1 directly and stimulates SIRT1 activity by enhancing the binding affinity of SIRT1 with Ac-p53 peptide, a native substrate peptide without a fluorogenic moiety. The binding affinity between SIRT1 and Ac-p53 peptide was enhanced 8.2-fold by KPMF-8 but only 1.4-fold by resveratrol. The specific binding sites of KPMF-8 to SIRT1 were mainly localized to the helix2-turn-helix3 motif in the N-terminal domain of SIRT1. Intracellular deacetylase activity in MCF-7 cells was promoted 1.7-fold by KPMF-8 supplemented in the cell medium but only 1.2-fold by resveratrol. This work reveals that KPMF-8 activates SIRT1 more effectively than resveratrol does.

Transcriptional control of the dihydroflavonol 4-reductase multigene family in Lotus japonicus.

In the genome of the model legume Lotus japonicus, dihydroflavonol 4-reductase (DFR), which is the first committed enzyme of the anthocyanin and proanthocyanidin (PA) pathways, is encoded as a tandemly arrayed five-gene family. Expression analysis revealed that both organ specificity and stress responsiveness differ among the DFRs. To elucidate the regulatory mechanisms underlying the expression of DFRs, we investigated the transcriptional control of each member of the DFR multigene family. Ectopic expression of a combination of the transcription factors MYB, bHLH, and WDR showed that only the DFR2 promoter was activated, indicating that each member of the DFR gene family is regulated independently.

Metabolome analysis using multiple data mining approaches suggests luteolin biosynthesis in Physcomitrella patens.

The model land plant Physcomitrella patens synthesizes flavonoids which may act as protectant of ultraviolet-B radiation. We aimed to uncover its flavonoid profile, for which metabolome analysis using liquid chromatography coupled with Ion trap/Orbitrap mass spectrometry was performed. From the 80% methanol extracts, 661 valid peaks were detected. Prediction of the elemental compositions within a mass accuracy of 2 ppm indicated that 217 peaks had single elemental composition. A compound database search revealed 47 peaks to be annotated as secondary metabolites based on the compound database search. Comprehensive substituent search by ShiftedIonsFinder showed there were 13 peaks of potential flavonoid derivatives. Interestingly, a peak having m/z 287.0551, corresponding to that of luteolin, was detected, even though flavone synthase has never been identified in P. patens. Using P. patens labeled with stable isotopes (13C-, 15N-, 18O-, and 34S), we confirmed the elemental composition of the peak as C15H10O6. By a comparison of MS/MS spectra with that of authentic standard, the peak was identified as luteolin or related flavone isomers. This is the first report of luteolin or related flavones synthesis and the possibility of the existence of an unknown enzyme with flavone synthase activity in P. patens.

[Determination of Absolute Purities of Hygroscopic Substances by Quantitative NMR Analysis for the Standardization of Quantitative Reagents in the Japanese Pharmacopoeia (Part 1)].

Quantitative NMR (qNMR) has been developed as an absolute quantitation method to determine the purity or content of organic compounds including marker compounds in crude drugs. The "qNMR test" has been introduced into the crude-drug section of the Japanese Pharmacopoeia (JP) for determining the purity of reagents used for the assay in the JP. In Supplement II to the JP 17th edition published in June 2019, fifteen compounds adopted qNMR test were listed as the reagents for the assay. To establish the "qNMR test" in the crude drug section of the JP, there were several problems to be solved. Previously, we reported that the handling impurity signals from reference substances and targeted marker compounds, chemical shifts of reference substances, and peak unity of signals of targeted marker compounds are important factors to conduct qNMR measurements with intended accuracy. In this study, we investigated that the hygroscopicity of reagents could cause the changes in the compounds' purity depending on increasing their water content. Twenty-one standard products used for the crude-drug test in JP were examined by water sorption-desorption analysis, and ginsenosides and saikosaponins were found to be hygroscopic. To prepare a sample solution of saikosaponin b2 for qNMR analysis, samples need to be maintained for 18 h at 25°C and 76% relative humidity; further, samples need to be weighed at the same humidity for the qNMR analysis.

[The Adverse Effects of Ephedra Herb and the Safety of Ephedrine Alkaloids-free Ephedra Herb Extract (EFE)].

Ephedra Herb is defined in the 17th edition of the Japanese Pharmacopoeia (JP) as the terrestrial stem of Ephedra sinica Stapf., Ephedra intermedia Schrenk et C.A. Meyer, or Ephedra equisetina Bunge (Ephedraceae). The stems of Ephedra Herb contain greater than 0.7% ephedrine alkaloids (ephedrine and pseudoephedrine). Despite its high effectiveness, Ephedra Herb exert several adverse effects, including palpitation, excitation, insomnia, and dysuria. Both the primary and adverse effects of Ephedra Herb have been traditionally believed to be mediated by these ephedrine alkaloids. However, our study found that several pharmacological actions of Ephedra Herb were not associated with ephedrine alkaloids. We prepared an ephedrine alkaloid-free Ephedra Herb extract (EFE) by eliminating ephedrine alkaloids from Ephedra Herb extract (EHE) using ion-exchange column chromatography. EFE exerted analgesic, anti-influenza, and anticancer activities in the same manner as EHE. Moreover, EFE did not induce adverse effects due to ephedrine alkaloids, such as excitation, insomnia, and arrhythmias, and showed no toxicity. Furthermore, we evaluated the safety of EFE in healthy volunteers. The number of adverse event cases was higher in the EHE-treated group than in the EFE-treated group, although the difference was not significant. Our evidence suggested that EFE was safer than EHE.

Identification and characterization of R2R3-MYB and bHLH transcription factors regulating anthocyanin biosynthesis in gentian flowers.

Gentian plants have vivid blue-colored flowers, caused by accumulation of a polyacylated anthocyanin 'gentiodelphin'. We previously performed expression analysis of gentiodelphin biosynthetic genes, and hypothesized that the white-flowered gentian cultivar 'Polarno White' might have resulted from the mutation of certain regulatory factors responsible for anthocyanin biosynthesis in flower petals. In this study, we isolated 26 R2R3-MYB gene fragments including four full-length cDNAs (GtMYB2a, GtMYB2b, GtMYB3 and GtMYB4) and one basic helix-loop-helix (bHLH) gene (GtbHLH1) from blue-flowered gentian by degenerate PCR and rapid amplification of cDNA ends (RACE). Phylogenetic tree analysis showed that GtMYB3 was categorized into a clade involved in anthocyanin biosynthesis including petunia AN2 and Arabidopsis PAP1. On the other hand, GtbHLH1 exhibited high identity with petunia AN1 based on both phylogenetic and genomic structural analyses. Temporal profiles of GtMYB3 and GtbHLH1 transcript levels corresponded well with those of gentiodelphin accumulation and their biosynthetic genes in petals. Yeast two-hybrid analysis showed that GtbHLH1 interacted with GtMYB3. Moreover, transient expression analysis indicated that the co-expression of GtMYB3 and GtbHLH1 could enhance the promoter activities of late anthocyanin biosynthetic genes in tobacco BY2 cells. We also revealed that in cv. 'Polarno White' the GtMYB3 genes were mutated by insertions of transposable elements or uncharacterized sequences, indicating that the white coloration was caused by GtMYB3 mutation. These results strongly suggested that GtMYB3 and GtbHLH1 are involved in the regulation of gentiodelphin biosynthesis in gentian flowers.

Differential gene expression profiles of red and green forms of Perilla frutescens leading to comprehensive identification of anthocyanin biosynthetic genes.

Differential screening by PCR-select subtraction was carried out for cDNAs from leaves of red and green perilla, two chemovarietal forms of Perilla frutescens regarding anthocyanin accumulation. One hundred and twenty cDNA fragments were selected as the clones preferentially expressed in anthocyanin-accumulating red perilla over the nonaccumulating green perilla. About half of them were the cDNAs encoding the proteins related presumably to phenylpropanoid-derived metabolism. The cDNAs encoding glutathione S-transferase (GST), PfGST1, and chalcone isomerase (CHI), PfCHI1, were further characterized. The expression of PfGST1 in an Arabidopsis thaliana tt19 mutant lacking the GST-like gene involved in vacuole transport of anthocyanin rescued the lesion of anthocyanin accumulation in tt19, indicating a function of PfGST1 in vacuole sequestration of anthocyanin in perilla. The recombinant PfCHI1 could stereospecifically convert naringenin chalcone to (2S)-naringenin. PfGST1 and PfCHI1 were preferentially expressed in the leaves of red perilla, agreeing with the accumulation of anthocyanin and expression of other previously identified genes for anthocyanin biosynthesis. These results suggest that the genes of the whole anthocyanin biosynthetic pathway are regulated in a coordinated manner in perilla.

Pathway-specific metabolome analysis with 18O2-labeled Medicago truncatula via a mass spectrometry-based approach.

INTRODUCTION: Oxygen from carbon dioxide, water or molecular oxygen, depending on the responsible enzyme, can lead to a large variety of metabolites through chemical modification. OBJECTIVES: Pathway-specific labeling using isotopic molecular oxygen (18O2) makes it possible to determine the origin of oxygen atoms in metabolites and the presence of biosynthetic enzymes (e.g., oxygenases). In this study, we established the basis of 18O2-metabolome analysis. METHODS: 18O2 labeled whole Medicago truncatula seedlings were prepared using 18O2-air and an economical sealed-glass bottle system. Metabolites were analyzed using high-accuracy and high-resolution mass spectrometry. Identification of the metabolite was confirmed by NMR following UHPLC-solid-phase extraction (SPE). RESULTS: A total of 511 peaks labeled by 18O2 from shoot and 343 peaks from root were annotated by untargeted metabolome analysis. Additionally, we identified a new flavonoid, apigenin 4'-O-[2'-O-coumaroyl-glucuronopyranosyl-(1-2)-O-glucuronopyranoside], that was labeled by 18O2. To the best of our knowledge, this is the first report of apigenin 4'-glucuronide in M. truncatula. Using MSn analysis, we estimated that 18O atoms were specifically incorporated in apigenin, the coumaroyl group, and glucuronic acid. For apigenin, an 18O atom was incorporated in the 4'-hydroxy group. Thus, non-specific incorporation of an 18O atom by recycling during one month of labeling is unlikely compared with the more specific oxygenase-catalyzing reaction. CONCLUSION: Our finding indicated that 18O2 labeling was effective not only for the mining of unknown metabolites which were biosynthesized by oxygenase-related pathway but also for the identification of metabolites whose oxygen atoms were derived from oxygenase activity.

Genome-wide analyses of the structural gene families involved in the legume-specific 5-deoxyisoflavonoid biosynthesis of Lotus japonicus.

A model legume Lotus japonicus (Regel) K. Larsen is one of the subjects of genome sequencing and functional genomics programs. In the course of targeted approaches to the legume genomics, we analyzed the genes encoding enzymes involved in the biosynthesis of the legume-specific 5-deoxyisoflavonoid of L. japonicus, which produces isoflavan phytoalexins on elicitor treatment. The paralogous biosynthetic genes were assigned as comprehensively as possible by biochemical experiments, similarity searches, comparison of the gene structures, and phylogenetic analyses. Among the 10 biosynthetic genes investigated, six comprise multigene families, and in many cases they form gene clusters in the chromosomes. Semi-quantitative reverse transcriptase-PCR analyses showed coordinate up-regulation of most of the genes during phytoalexin induction and complex accumulation patterns of the transcripts in different organs. Some paralogous genes exhibited similar expression specificities, suggesting their genetic redundancy. The molecular evolution of the biosynthetic genes is discussed. The results presented here provide reliable annotations of the genes and genetic markers for comparative and functional genomics of leguminous plants.

Degradation Index for quality evaluation of commercial dietary supplements of bilberry extract.

In recent years, many anthocyanin-containing dietary supplements of various dosages and formulations have been sold through advertising their large number of beneficial effects. On the other hand, there is an increased risk of distributing deteriorated supplements to consumers due to lax regulations, because in Japan these supplements are classified as food. Spectrophotometric methods are commonly used to control the quality of supplements. However, these methods have limitations with regard to assessing deterioration. In this study, we evaluated a new index for detection of deteriorated products. The stability of 3 formulations and the quality of 20 supplements were investigated by ultra-high performance liquid chromatography, which is superior to spectrophotometry for identifying and quantifying individual anthocyanins. The stability was not only affected by storage temperature but also by formulation. We defined "Degradation Index" (DI) as an indicator of the deterioration of supplements. Of 20 supplements investigated, the DI of 5 supplements was more than 3-fold the value of Bilberon-25, and the worst one was 12.7-fold. These results suggest that DI could be a useful quality control index for detecting deteriorated supplements.

A single-base deletion in soybean flavonol synthase gene is associated with magenta flower color.

The Wm locus of soybean [Glycine max (L.) Merr.] controls flower color. Dominant Wm and recessive wm allele of the locus produce purple and magenta flower, respectively. A putative full-length cDNA of flavonol synthase (FLS), gmfls1 was isolated by 5' RACE and end-to-end PCR from a cultivar Harosoy with purple flower (WmWm). Sequence analysis revealed that gmfls1 consisted of 1,208 nucleotides encoding 334 amino acids. It had 59-72% homology with FLS proteins of other plant species. Conserved dioxygenase domains A and B were found in the deduced polypeptide. Sequence comparison between Harosoy and Harosoy-wm (magenta flower mutant of Harosoy; wmwm) revealed that they differed by a single G deletion in the coding region of Harosoy-wm. The deletion changed the subsequent reading frame resulting in a truncated polypeptide consisting of 37 amino acids that lacked the dioxygenase domains A and B. Extracts of E. coli cells expressing gmfls1 of Harosoy catalyzed the formation of quercetin from dihydroquercetin, whereas cell extracts expressing gmfls1 of Harosoy-wm had no FLS activity. Genomic Southern analysis suggested the existence of three to four copies of the FLS gene in the soybean genome. CAPS analysis was performed to detect the single-base deletion. Harosoy and Clark (WmWm) exhibited longer fragments, while Harosoy-wm had shorter fragments due to the single-base deletion. The CAPS marker co-segregated with genotypes at Wm locus in a F(2) population segregating for the locus. Linkage mapping using SSR markers revealed that the Wm and gmfls1 were mapped at similar position in the molecular linkage group F. The above results strongly suggest that gmfls1 represents the Wm gene and that the single-base deletion may be responsible for magenta flower color.

A comprehensive analysis of six dihydroflavonol 4-reductases encoded by a gene cluster of the Lotus japonicus genome.

Dihydroflavonol 4-reductase (DFR) is the first committed enzyme of the anthocyanin and condensed tannin pathways. Several DFR cDNAs have been cloned, and different specificities of DFR isozymes in the substrate hydroxylation patterns have been reported, but only fragmentary knowledge of DFR gene organization is available. Reported here is a comprehensive analysis of DFRs of a model legume, Lotus japonicus. A total of five DFR genes were found to form a cluster within a 38 kb region in the L. japonicus genome, whereas six cDNAs, including two splicing variants resulting from a transversion at a splicing acceptor site, were cloned. All the genes were expressed, with different organ specificities, in the mature plant. Three of the DFR proteins heterologously expressed in Escherichia coli showed catalytic activity, and their substrate preferences agreed with the variation of a specific active site residue (Asp or Asn) reported to control the specificity. The hydroxylation patterns of anthocyanidins and condensed tannin units in the stems did not reflect the substrate specificity of the expressed isozymes, implying complex regulation mechanisms in the biosynthesis. The two splicing variants and one DFR with Ser at the specificity-controlling position failed to show the activity, but a revertant protein replacing the unusual splicing restored the activity. The phylogenetic tree, constructed with known DFR sequences, showed evolutionary divergence of some of the DFR genes prior to the plant speciation. This work affords the basis for genetic and biochemical studies on the diversity of DFR and the flavonoid products.

cDNA cloning and biochemical characterization of S-adenosyl-L-methionine: 2,7,4'-trihydroxyisoflavanone 4'-O-methyltransferase, a critical enzyme of the legume isoflavonoid phytoalexin pathway.

Formononetin (7-hydroxy-4'-methoxyisoflavone, also known as 4'-O-methyldaidzein) is an essential intermediate of ecophysiologically active leguminous isoflavonoids. The biosynthetic pathway to produce 4'-methoxyl of formononetin has been unknown because the methyl transfer from S-adenosyl-L-methionine (SAM) to 4'-hydroxyl of daidzein has never been detected in any plants. A hypothesis that SAM: daidzein 7-O-methyltransferase (D7OMT), an enzyme with a different regiospecificity, is involved in formononetin biosynthesis through its intracellular compartmentation with other enzymes recently prevails, but no direct evidence has been presented. We proposed a new scheme of formononetin biosynthesis involving 2,7,4'-trihydroxyisoflavanone as the methyl acceptor and subsequent dehydration. We now cloned a cDNA encoding SAM: 2,7,4'-trihydroxyisoflavanone 4'-O-methyltransferase (HI4'OMT) through the screening of functionally expressed Glycyrrhiza echinata (Fabaceae) cDNAs. The reaction product, 2,7-dihydroxy-4'-methoxyisoflavanone, was unambiguously identified. Recombinant G. echinata D7OMT did not show HI4'OMT activity, and G. echinata HI4'OMT protein free from D7OMT was partially purified. HI4'OMT is thus concluded to be distinct from D7OMT, and their distant phylogenetic relationship was further presented. HI4'OMT may be functionally identical to (+)-6a-hydroxymaackiain 3-OMT of pea. Homologous cDNAs were found in several legumes, and the catalytic function of the Lotus japonicus HI4'OMT was verified, indicating that HI4'OMT is the enzyme of formononetin biosynthesis in general legumes.

A cluster of genes encodes the two types of chalcone isomerase involved in the biosynthesis of general flavonoids and legume-specific 5-deoxy(iso)flavonoids in Lotus japonicus.

Leguminous plants produce 5-deoxyflavonoids and 5-deoxyisoflavonoids that play essential roles in legume-microbe interactions. Together with chalcone polyketide reductase and cytochrome P450 2-hydroxyisoflavanone synthase, the chalcone isomerase (CHI) of leguminous plants is fundamental in the construction of these ecophysiologically active flavonoids. Although CHIs of nonleguminous plants isomerize only 6'-hydroxychalcone to 5-hydroxyflavanone (CHIs with this function are referred to as type I), leguminous CHIs convert both 6'-deoxychalcone and 6'-hydroxychalcone to 5-deoxyflavanone and 5-hydroxyflavanone, respectively (referred to as type II). In this study, we isolated multiple CHI cDNAs (cCHI1-cCHI3) from a model legume, Lotus japonicus. In contrast to previous observations, the amino acid sequence of CHI2 was highly homologous to nonleguminous CHIs, whereas CHI1 and CHI3 were the conventional leguminous type. Furthermore, genome sequence analysis revealed that four CHI genes (CHI1-3 and a putative gene, CHI4) form a tandem cluster within 15 kb. Biochemical analysis with recombinant CHIs expressed in Escherichia coli confirmed that CHI1 and CHI3 are type II CHIs and that CHI2 is a type I CHI. The occurrence of both types of CHIs is probably common in leguminous plants, and it was suggested that type II CHIs evolved from an ancestral CHI by gene duplication and began to produce 5-deoxy(iso)flavonoids along with the establishment of the Fabaceae.