Genome-wide identification and expression profiling of the HMGR gene family in Bupleurum chinense DC.

Bupleurum chinense DC. is a commonly used medicinal plant, and the main bioactive compounds are saikosaponins (SSs), which significantly influence its therapeutic quality. 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) is the first rate-limiting enzyme in the mevalonate (MVA) pathway, providing precursors for SSs biosynthesis. The lack of studies on the HMGR gene family in B. chinense has limited further understanding of the SSs biosynthesis mechanism. This study performed a genome-wide analysis of the BcHMGR gene family, including phylogenetic and gene structure analysis, cis-elements prediction, quantitative real-time PCR (qRT-PCR) in different tissues, and high-performance liquid chromatography (HPLC) analysis after phytohormone treatments, and explored the potential relationship between BcHMGR expression and SSs biosynthesis.

Four Bupleurum chinense HMGR genes (BcHMGRs) were classified into two subfamilies, distributed across two chromosomes, and appeared to have expanded via segmental duplication. The BcHMGR proteins may possess highly conserved catalytic domains, and their promoters contain stress- and hormone-responsive cis-elements. Phytohormone treatments regulated BcHMGR expression and influenced SSs accumulation in a genotype-dependent manner. BcHMGR1, BcHMGR3, and BcHMGR4 showed root-predominant expression across most genotypes. This pattern is consistent with the accumulation sites of SSs and suggests a potential association. In particular, the relative expression levels of BcHMGR3 and BcHMGR4 showed significant increases after exogenous hormone treatment. These results suggest that they may be candidate genes involved in SSs biosynthesis, although their specific functions still require further verification.

These findings provide candidate genes for future functional studies and potential regulation of SSs production in B. chinense and offer a theoretical basis for future metabolic engineering and artificial control of SSs biosynthesis.