Identification of WRKY Transcription Factors Related to Saikosaponin Biosynthesis in Adventitious Roots of Bupleurum chinense

Objective To identify the genes of WRKY transcription factors (TFs) from roots of Bupleurum chinense and genes that potentially regulate saikosaponin (SS) biosynthesis. Methods Firstly, the subfamily cluster analysis was mainly based on Arabidopsis thaliana WRKYs for 27 putative WRKY TFs selected from previous transcriptome sequencing data. Secondly, qPCR was used to screen such genes of WRKY TFs that could be induced by NaCl and PEG6000 in adventitious roots of B. chinense. Meanwhile, saikosaponins (SSs) in treated adventitious roots were determined by HPLC. The roots were collected at 0, 2, 4, 8, 12, 24, 48, and 72 h after treatments, and 120 h only for PEG. Finally, the tissue-specific expression was analyzed on screened genes by qPCR. Results The 27 genes were grouped into three categories: There were nine in Group I, 15 in Group II, and two in Group III. Four genes of WRKYTFs, BCWRKY6, BCWRKY16, BCWRKY32, and BCWRKY35 were obviously induced by NaCl in adventitious roots of B. chinense, while only BCWRKY32 was induced by PEG. The content of SSs increased at different levels in NaCl and PEG6000 treatment. Three genes including BCWRKY6, BCWRKY32, and BCWRKY35, expressed most in roots, were similar to the accumulation pattern of SS. Conclusion The three WRKY genes, BCWRKY6, BCWRKY32, and BCWRKY35, may be involved in the biosynthesis of SS.