Genome-Wide Identification and Expression Analysis of SS and SE Gene Families in Platycodon grandiflorum

At present, the characteristics of key enzyme genes in the upstream pathway for triterpenoid saponin biosynthesis in P. grandiflorum, as well as their expression patterns over the growth duration, have not been systematically analyzed. This study, at the whole-genome level, conducts the first bioinformatics and expression analyses of the SS and SE gene families in P. grandiflorum. Four PgSS and seven PgSE genes were identified and distributed across six chromosomes. Members within the same subfamily exhibited highly conserved sequences and structures, while distinct structural divergence was observed between different subfamilies. Phylogenetic analysis showed that PgSS and PgSE genes were closely related to those of dicotyledons such as Panax ginseng and Polygala tenuifolia, suggesting high evolutionary conservation. Promoter analysis revealed abundant light- and hormone-responsive elements and MYB/MYC binding sites, indicating regulation by multiple signals. Protein secondary structures were dominated by the Alpha helix and were structurally stable. Quantitative real-time polymerase chain reaction (qPCR) demonstrated that expression levels of PgSS and PgSE in one-year-old Platycodonis Radix were significantly higher than in perennial Platycodonis Radix, especially for the PgSE family. This study characterized the basic biological features and growth-stage-dependent expression patterns of the SS and SE gene families in P. grandiflorum. The results identify key candidate genes and molecular targets for regulating triterpenoid saponin biosynthesis, and provide data supporting quality improvement and active metabolite research in this medicinal plant.