Overexpression of BcbZIP134 negatively regulates the biosynthesis of saikosaponins

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.