Overexpression of BcbZIP134 negatively regulates the biosynthesis of saikosaponins

Abstract

Chaihu, the dried roots of several Bupleurum species, are widely used as herbal drugs. Triterpene saponins, as saikosaponins (SSs) in Chaihu, exhibit a wide range of pharmacological actions, including significant anti-inflammatory, immunomodulatory, hepatoprotective, antioxidant, anti-tumor and antiviral activities. To explore the regulatory biosynthesis of SS in Bupleurum chinense roots, we screened putative transcription factor (TF) genes from transcriptome data. Here, we report one of the bZIP TF genes, named BcbZIP134, which belongs to bZIP G subfamily. The expression of BcbZIP134 was elevated in MeJA-treated adventitious roots of B. chinense. No obvious differential expression of BcbZIP134 was detected in tissues (root, stem, leaf, flower and fruit) of B. chinense. Overexpressing BcbZIP134 in B. chinense hairy roots revealed that the content of the main SS monomers a, c and d were decreased compared to control hairy roots. Furthermore, the contents of a few other minor SS monomers were also affected when compared to the controls. The results indicate that BcbZIP134 may play a negative regulatory role in SS biosynthesis. Key MessageChaihu, the dried roots of several Bupleurum species, are successfully and widely used as herbal drugs. Triterpene saponins, as saikosaponins (SSs) in Chaihu, exhibit a wide range of pharmacological actions, including significant anti-inflammatory, immunomodulatory, hepatoprotective, antioxidant, anti-tumor and antiviral activities. To explore the regulatory biosynthesis of SS in B. chinense roots, we screened putative transcription factor (TF) genes from transcriptome data. Here, we report one of the bZIP TF genes, named BcbZIP134, which encodes a predicted 410 amino acid protein belonging to bZIP G subfamily. The expression of BcbZIP134 was elevated in MeJA-treated adventitious roots of B. chinense, and no obvious differential expression of BcbZIP134 was detected in tissues (root, stem, leaf, flower and fruit) of B. chinense. Overexpressing BcbZIP134 in B. chinense hairy roots revealed that the content of the main SS monomers a, c and d were decreased compared to control hairy roots. Furthermore, the contents of a few other minor SS monomers were also affected when compared to the controls.The results indicate that BcbZIP134 may play a negative regulatory role in SS biosynthesis.

Comparative Transcriptome and Phytochemical Analysis Provides Insight into Triterpene Saponin Biosynthesis in Seeds and Flowers of the Tea Plant (Camellia sinensis)

“…An ERF TF (PjERF1) from Panax japonicus were proven to bind with the promoters of βAS , CAS and SE , and regulated triterpene saponin biosynthesis [ 40 ]. A bZIP TF gene BcbZIP134 negatively regulated the biosynthesis of saikosaponins in the roots of Chaihu [ 41 ]. In this study, a total of 27 TFs were obtained after WGCNA analysis.…”

Metabolome and Transcriptome Analysis Reveals the Transcriptional Regulatory Mechanism of Triterpenoid Saponin Biosynthesis in Soapberry (Sapindus mukorossi Gaertn.)

“…More evidence supported that the evolution of the triterpenoid saponin pathway in different plants is independent and convergent. , Several possible routes of triterpenoid saponin biosynthesis have been identified in plants and confirmed to be similar. , The whole triterpenoid saponin pathway can be divided into three stages: isopentenyl diphosphate (IPP) and its isomer, dimethylallyl diphosphate (DMAPP), derived either from condensation of acetyl-CoA in the cytosolic mevalonic acid (MVA) pathway or from pyruvate and phosphoglyceraldehyde in the plastidial 2- C -methyl- d -erythritol 4-phosphate (MEP) pathway; IPP and DMAPP are catalyzed by the corresponding enzymes to produce 2,3-oxidosqualene; and 2,3-oxidosqualene is cyclized to a triterpenoid backbone by oxidosqualene cyclases (OSCs). These molecules are then chemically modified by cytochrome P450 monooxygenase (CYP450) and uridine diphosphate (UDP)-glycosyltransferase (UGT), resulting in the production of different types of triterpenoid saponins. − Several transcription factors (TFs) have been reported to be involved in the biosynthesis of triterpenoid saponins by regulating the expression of saponin biosynthetic genes, such as bHLH, AP2/ERF, bZIP, and WRKY …”

Chromosome-Level Genome Assembly of Bupleurum chinense DC Provides Insights Into the Saikosaponin Biosynthesis

“…More than 120 glycosylated oleanane-types and ursane-types of saponins have been isolated from Bupleurum . The most predominant SS monomers in Bupleurum are SS-a, SS-c, and SS-d ( Xu et al, 2019 ). These different SSs monomers exhibit different pharmacological effects.…”