Comprehensive Identification of CPP Gene Family Members in Panax ginseng and Expression Analysis of PgCPP and Key Protopanaxadiol Ginsenoside Biosynthesis Genes in Response to MeJA

The Cysteine-rich Polycomb-like Protein (CPP) gene family is a class of transcription factors containing conserved CXC domains that are widely involved in the regulation of plant growth and development, cell division, and stress responses. Based on the ginseng genome and transcriptome database, all members of the PgCPP gene family in Panax ginseng were systematically identified, and comprehensive bioinformatics analyses, including phylogenetic, conserved domain, chromosomal localization and collinearity, cis-acting element, and expression pattern analyses, were conducted. In this study, we identified 44 PgCPP gene family members in ginseng, which were unevenly localized on multiple chromosomes. The phylogenetic tree divided them into three subfamilies, with members in the same subfamily being highly conserved. Conserved domain analysis revealed that all PgCPPs contain typical CXC motifs. Cis-acting elements were abundant in light response, hormone responses (abscisic acid, methyl jasmonate, salicylic acid), and stress response elements. Expression heatmaps demonstrated that different members have specific expression patterns across different ages, tissues, and species. After treatment with MeJA, transcriptional suppression of PgCPP03-4 and PgCPP03-13 was observed, and their expression levels demonstrated significant negative correlations with the contents of six protopanaxadiol-type ginsenosides. These findings suggest that PgCPP03-4 and PgCPP03-13 may act as negative regulators of protopanaxadiol-type ginsenoside biosynthesis within the MeJA signaling pathway. This systematic characterization and identification of the CPP gene family members in P. ginseng establishes a foundational framework for future functional validation and molecular breeding initiatives.