Metabolite Profiling and Transcriptome Analysis Explain the Difference in Accumulation of Bioactive Constituents in Taxilli Herba from Two Hosts

Taxilli Herba (TH) is a semi-parasitic herb and the host is a key factor affecting its quality. Flavonoids are the main bioactive constituents in TH. However, studies on the difference in accumulation of flavonoids in TH from different hosts are vacant. In this study, integrated transcriptomic and metabolomic analyses were performed on TH from Morus alba L. (SS) and Liquidambar formosana Hance (FXS) to investigate the relationship between the regulation of gene expression and the accumulation of bioactive constituents. The results showed that a total of 3319 differentially expressed genes (DEGs) were screened in transcriptomic analysis, including 1726 up-regulated genes and 1547 down-regulated genes. In addition, 81 compounds were identified using ultra-fast performance liquid chromatography coupled with triple quadrupole-time of flight ion trap tandem mass spectrometry (UFLC-Triple TOF-MS/MS) analysis, and the relative contents of flavonol aglycones and glycosides were higher in TH from SS group than those from the FXS group. A putative biosynthesis network of flavonoids was created, combined with structural genes, and the expression patterns of genes were mostly consistent with the variation of bioactive constituents. It was noteworthy that the UDP-glycosyltransferase genes might participate in downstream flavonoid glycosides synthesis. The findings of this work will provide a new way to understand the quality formation of TH from the aspects of metabolite changes and molecular mechanism.

Metabolite Profiling and Transcriptome Analysis Explains Difference in Accumulation of Bioactive Constituents in Licorice (Glycyrrhiza uralensis) Under Salt Stress

Salinity stress significantly affects the contents of bioactive constituents in licorice Glycyrrhiza uralensis. To elucidate the molecular mechanism underlying the difference in the accumulation of these constituents under sodium chloride (NaCl, salt) stress, licorice seedlings were treated with NaCl and then subjected to an integrated transcriptomic and metabolite profiling analysis. The transcriptomic analysis results identified 3,664 differentially expressed genes (DEGs) including transcription factor family MYB and basic helix-loop-helix (bHLH). Most DEGs were involved in flavonoid and terpenoid biosynthesis pathways. In addition, 121 compounds including a triterpenoid and five classes of flavonoids (isoflavone, flavone, flavanone, isoflavan, and chalcone) were identified, and their relative levels were compared between the stressed and control groups using data from the ultrafast liquid chromatography (UFLC)-triple quadrupole-time of flight-tandem mass spectrometry (TOF-MS/MS) analysis. Putative biosynthesis networks of the flavonoids and triterpenoids were created and combined with structural DEGs such as phenylalanine ammonia-lyase (PAL), 4-coumarate-CoA ligase [4CL], cinnamate 4-hydroxylase [C4H], chalcone synthase [CHS], chalcone-flavanone isomerase [CHI], and flavonoid-3',5' hydroxylase (F3',5'H) for flavonoids, and CYP88D6 and CYP72A154 for glycyrrhizin biosynthesis. Notably, significant upregulation of UDP-glycosyltransferase genes (UGT) in salt-stressed licorice indicated that postmodification of glycosyltransferase may participate in downstream biosynthesis of flavonoid glycosides and triterpenoid saponins. Accordingly, the expression trend of the DEGs is positively correlated with the accumulation of glycosides. Our study findings indicate that key DEGs and crucial UGT genes co-regulate flavonoid and saponin biosynthesis in licorice under salt stress.