Search

The 4-coumarate: CoA ligase(4CL) is a key enzyme in the upstream pathway of phenylpropanoids such as flavonoids, soluble phenolic esters, lignans, and lignins in plants. In this study, 13 4CL family members of Arabidopsis thaliana were used as reference sequences to identify the 4CL gene family candidate members of Isatis indigotica from the reported I. indigotica genome. Further bioinformatics analysis and analysis of the expression pattern of 4CL genes and the accumulation pattern of flavonoids were carried out. Thirteen 4CL genes were obtained, named Ii4CL1-Ii4CL13, which were distributed on chromosomes 1, 2, 3, 4, and 6. The analysis of the gene structure and conserved structural domains revealed the intron number of I. indigotica 4CL genes was between 1 and 12 and the protein structural domains were highly conserved. Cis-acting element analysis showed that there were multiple response elements in the promoter sequence of I. indigotica 4CL gene family, and jasmonic acid had the largest number of reaction elements. The collinearity analysis showed that there was a close relationship between the 4CL gene family members of I. indigotica and A. thaliana. As revealed by qPCR results, the expression analysis of the 4CL gene family showed that 10 4CL genes had higher expression levels in the aboveground part of I. indigotica. The content assay of flavonoids in different parts of I. indigotica showed that flavonoids were mainly accumulated in the aboveground part of plants. This study provides a basis for further investigating the roles of the 4CL gene family involved in the biosynthesis of flavonoids in I. indigotica.

Dead heart is an important trait of pith-decayed Scutellariae Radix. The purpose of this study was to clarify the scientific connotation of the dead heart using multi-omics. Metabolomics and transcriptomics combined with multivariate statistical analysis such as principal component analysis(PCA) and partial least squares discriminant analysis(PLS-DA) were used to systematically compare the differences in chemical composition and gene expression among phloem, outer xylem and near-dead xylem of pith-decayed Scutella-riae Radix. The results revealed significant differences in the contents of flavonoid glycosides and aglycones among the three parts. Compared with phloem and outer xylem, near-dead xylem had markedly lowered content of flavonoid glycosides(including baicalin, norwogonin-7-O-β-D-glucuronide, oroxylin A-7-O-β-D-glucuronide, and wogonoside) while markedly increased content of aglycones(including 3,5,7,2',6'-pentahydroxy dihydroflavone, baicalin, wogonin, and oroxylin A). The differentially expressed genes were mainly concentrated in KEGG pathways such as phenylpropanoid metabolism, flavonoid biosynthesis, ABC transporter, and plant MAPK signal transduction pathway. This study systematically elucidated the material basis of the dead heart of pith-decayed Scutellariae Radix with multiple growing years. Specifically, the content of flavonoid aglycones was significantly increased in the near-dead xylem, and the gene expression of metabolic pathways such as flavonoid glycoside hydrolysis, interxylary cork development and programmed apoptosis was significantly up-regulated. This study provided a theoretical basis for guiding the high-quality production of pith-decayed Scutellariae Radix.

Chalcone isomerase is a key rate-limiting enzyme in the biosynthesis of flavonoids in higher plants, which determines the production of flavonoids in plants. In this study, RNA was extracted from different parts of Isatis indigotica and reverse-transcribed into cDNA. Specific primers with enzyme restriction sites were designed, and a chalcone isomerase gene was cloned from I. indigotica, named IiCHI. IiCHI was 756 bp in length, containing a complete open reading frame and encoding 251 amino acids. Homology analysis showed that IiCHI was closely related to CHI protein of Arabidopsis thaliana and had typical active sites of chalcone isomerase. Phylogenetic tree analysis showed that IiCHI was classified into type Ⅰ CHI clade. Recombinant prokaryotic expression vector pET28a-IiCHI was constructed and purified to obtain IiCHI recombinant protein. In vitro enzymatic analysis showed that the IiCHI protein could convert naringenin chalcone into naringenin, but could not catalyze the production of liquiritigenin by isoliquiritigenin. The results of real-time quantitative polymerase chain reaction(qPCR) showed that the expression level of IiCHI in the aboveground parts was higher than that in the underground parts and the expression level was the highest in the flowers of the aboveground parts, followed by leaves and stems, and no expression was observed in the roots and rhizomes of the underground parts. This study has confirmed the function of chalcone isomerase in I. indigotica and provided references for the biosynthesis of flavonoid components.

Based on the transcriptome data of Isatis indigotica, a total of 110 putative glycosytransferases were identified. Through prokaryotic expression and enzymic activity assay in vitro, a novel lignan glycosyltransferase gene was screened out and named IiUGT349, which catalyzed lariciresinol into lariciresinol-4-O-β-D-glucoside and lariciresinol-4'-O-β-D-glucoside. Bioinformatics analysis suggested that IiUGT349 contained an open reading frame(ORF) of 1 401 bp encoding a protein of 467 amino acids. A protein analysis indicated that IiUGT349 have a predecited molecular weight of 52.77 kDa and pI of 5.96. Phylogenetic analysis showed that IiUGT349 belonging to UGT90 family shared low amino acid sequence identity with the reported lignan glycosyltransferases, which may represent a novel type of lignan glycosyltransferases. Quantitative real-time PCR(qRT-PCR) analysis showed that IiUGT349 was expressed in roots, stems, young leaves and leaves, with the highest expression level in stems. Further biochemical analysis showed that the optimal reaction time of IiUGT349 recombinant protein was 12 h and the optimal temperature was 45 ℃. Subcellular localization demonstrated that IiUGT349 was located in the cytoplasm and nucleus of plants. In this study, a new glucosyltransferase gene IiUGT349 from I. indigotica belonging to the UGT90 family was cloned, which laid a foundation to further investigate its' function and elucidate the lignan glycosides biosynthesis pathway and plays an important role for great significance for the synthetic biology of active lignan glycosides.

The lignan glycosyltransferase UGT236(belonging to the UGT71 B family) from Isatis indigotica can catalyze the production of phloridzin from phloretin in vitro. UGT236 shares high identity with P2'GT from apple. In this study, the recombinant plasmid pET28 a-MBP-UGT236 was transferred into Escherichia coli Rosetta(DE3) cells and induced by isopropyl-β-D-thiogalactoside(IPTG). The purified UGT236 protein was used for enzymatic characterization with phloretin as substrate. The results showed that UGT236 had the optimal reaction temperature of 40 ℃ and the optimal pH 8(Na_2HPO_4-NaH_2PO_4 system). The UGT236 activity was inhibited by Ni~(2+) and Al~(3+), enhanced by Fe~(2+), Co~(2+), and Mn~(2+), and did not affected by Mg~(2+), Ca~(2+), Li~+, Na~+, or K~+. The K_m, K_(cat), and K_(cat)/K_m of phloretin were 61.03 μmol·L~(-1), 0.01 s~(-1), and 157.11 mol~(-1)·s~(-1)·L, and those of UDPG were 183.6 μmol·L~(-1), 0.01 s~(-1), and 51.91 mol~(-1)·s~(-1)·L, respectively. The possible active sites were predicted by homologous modeling and molecular docking. By mutagenisis and catalytic activity detection, three key active sites, Glu391, His15, and Thr141, were identified, while Phe146 was related to product diversity. In summary, we found that the lignan glycosyltransferase UGT236 from I.indigotica could catalyze the reaction of phloretin into phloridzin. Several key amino acid residues were identified by structure prediction, molecular docking, and site-mutagenesis, which provided a basis for studying the specificity and diversity of phloretin glycoside products. This study can provide a reference for artificially producing glycosyltransferase elements with high efficiency and specific catalysis.