Galloylated catechins and flavonol 3-O-glycosides are characteristic astringent taste compounds in tea (Camellia sinensis). The mechanism involved in the formation of these metabolites remains unknown in tea plants. In this paper, 178 UGT genes (CsUGTs) were identified in C. sinensis based on an analysis of tea transcriptome data. Phylogenetic analysis revealed that 132 of these genes were clustered into 15 previously established phylogenetic groups (A to M, O and P) and a newly identified group R. Three of the 11 recombinant UGT proteins tested were found to be involved in the in vitro biosynthesis of β-glucogallin and glycosylated flavonols. CsUGT84A22 exhibited catalytic activity toward phenolic acids, in particular gallic acid, to produce β-glucogallin, which is the immediate precursor of galloylated catechin biosynthesis in tea plants. CsUGT78A14 and CsUGT78A15 were found to be responsible for the biosynthesis of flavonol 3-O-glucosides and flavonol 3-O-galactosides, respectively. Site-directed mutagenesis of the Q373H substitution for CsUGT78A14 indicated that the Q (Gln) residue played a catalytically crucial role for flavonoid 3-O-glucosyltransferase activity. The expression profiles of the CsUGT84A22, CsUGT78A14, and CsUGT78A15 genes were correlated with the accumulation patterns of β-glucogallin and the glycosylated flavonols which indicated that these three CsUGT genes were involved in the biosynthesis of astringent compounds in C. sinensis.

Ginseng, which contains ginsenosides as bioactive compounds, has been regarded as an important traditional medicine for several millennia. However, the genetic background of ginseng remains poorly understood, partly because of the plant's large and complex genome composition. We report the entire genome sequence of Panax ginseng using next-generation sequencing. The 3.5-Gb nucleotide sequence contains more than 60% repeats and encodes 42 006 predicted genes. Twenty-two transcriptome datasets and mass spectrometry images of ginseng roots were adopted to precisely quantify the functional genes. Thirty-one genes were identified to be involved in the mevalonic acid pathway. Eight of these genes were annotated as 3-hydroxy-3-methylglutaryl-CoA reductases, which displayed diverse structures and expression characteristics. A total of 225 UDP-glycosyltransferases (UGTs) were identified, and these UGTs accounted for one of the largest gene families of ginseng. Tandem repeats contributed to the duplication and divergence of UGTs. Molecular modeling of UGTs in the 71st, 74th, and 94th families revealed a regiospecific conserved motif located at the N-terminus. Molecular docking predicted that this motif captures ginsenoside precursors. The ginseng genome represents a valuable resource for understanding and improving the breeding, cultivation, and synthesis biology of this key herb.

Flavonoids are important natural products for plant defence and human health. Although almost all the flavonoid pathway genes have been well-documented by biochemical and/or genetic approaches, the role of the Arabidopsis chalcone isomerase-like (CHIL) gene remains unclear. Two chil mutants with a seed colour similar to that of wild-type Arabidopsis have been identified here, but in sharp contrast to the characteristic transparent testa seed phenotype associated with other known flavonoid pathway genes. CHIL loss-of-function mutations led to a strong reduction in the proanthocyanidin and flavonol levels in seeds, but not in the anthocyanin levels in leaves. CHIL over-expression could partially recover the mutant phenotype of the chil mutant and increased both proanthocyanidin and flavonol accumulation in wild-type Arabidopsis. However, the CHIL gene could not rescue the mutant phenotype of TT5 that encodes the intrinsic chalcone isomerase in Arabidopsis. Parallel phenotypical and metabolic analyses of the chil, tt5, chs, and f3h mutants revealed that, genetically, CHIL functions at the same step as TT5. Moreover, it is demonstrated that CHIL co-expresses, co-localizes, and interacts with TT5 in Arabidopsis for flavonoid production. Based on these genetic and metabolic studies, it is concluded that CHIL functions with TT5 to promote flavonoid production, which is a unique enhancer in the flavonoid pathway.

Flavonoids, natural products abundant in the model legume Glycine max, confer benefits to plants and to animal health. Flavonoids are present in soybean mainly as glycoconjugates. However, the mechanisms of biosynthesis of flavonoid glycosides are largely unknown in G. max. In the present study, 212 putative UDP-glycosyltransferase (UGT) genes were identified in G. max by genome-wide searching. The GmUGT genes were distributed differentially among the 20 chromosomes, and they were expressed in various tissues with distinct expression profiles. We further analyzed the enzymatic activities of 11 GmUGTs that are potentially involved in flavonoid glycosylation, and found that six of them (UGT72X4, UGT72Z3, UGT73C20, UGT88A13, UGT88E19 and UGT92G4) exhibited activity toward flavonol, isoflavone, flavone and flavanol aglycones with different kinetic properties. Among them, UGT72X4, UGT72Z3 and UGT92G4 are flavonol-specific UGTs, and UGT73C20 and UGT88E19 exhibited activity toward both flavonol and isoflavone aglycones. In particular, UGT88A13 exhibited activity toward epicatechin, but not for the flavonol aglycones kaempferol and quercetin. Overexpression of these six GmUGT genes significantly increased the contents of isoflavone and flavonol glucosides in soybean hairy roots. In addition, overexpression of these six GmUGT genes also affected flavonol glycoside contents differently in seedlings and seeds of transgenic Arabidopsis thaliana. We provide valuable information on the identification of all UGT genes in soybean, and candidate GmUGT genes for potential metabolic engineering of flavonoid compounds in both Escherichia coli and plants.

Horse chestnut (Aesculus chinensis) is an important medicinal tree that contains various bioactive compounds, such as aescin, barrigenol-type triterpenoid saponins (BAT), and aesculin, a glycosylated coumarin. Herein, we report a 470.02 Mb genome assembly and characterize an Aesculus-specific whole-genome duplication event, which leads to the formation and duplication of two triterpenoid biosynthesis-related gene clusters (BGCs). We also show that AcOCS6, AcCYP716A278, AcCYP716A275, and AcCSL1 genes within these two BGCs along with a seed-specific expressed AcBAHD6 are responsible for the formation of aescin. Furthermore, we identify seven Aesculus-originated coumarin glycoside biosynthetic genes and achieve the de novo synthesis of aesculin in E. coli. Collinearity analysis shows that the collinear BGC segments can be traced back to early-diverging angiosperms, and the essential gene-encoding enzymes necessary for BAT biosynthesis are recruited before the splitting of Aesculus, Acer, and Xanthoceras. These findings provide insight on the evolution of gene clusters associated with medicinal tree metabolites.