Genome-Wide Characterization and Expression Analysis of the Cysteine-Rich Polycomb-like Protein Gene Family in Response to Hormone Signaling in Apple ().

Cysteine-rich polycomb-like protein (CPP) transcription factors play critical roles in plant growth, development, and responses to stresses and hormone signaling. However, the research on the gene family remains unexplored in apple. In this study, a total of 10 genes (-) were identified and unevenly distributed across seven scaffolds. Phylogenetic and conserved motif analyses revealed that these 10 CXC domain-containing MdCPPs could be classified into three subfamilies. Evolutionary tree and synteny analyses demonstrated that apple shared the highest number of orthologous gene pairs with white pear compared to . By analyzing the gene promoter, a large number of -acting elements related to hormone and stress response were discovered. In addition, transcriptomic data demonstrated tissue-specific expression patterns of genes, with and showing the highest expression in buds and leaves. The qRT-PCR results indicated that genes have different expression responses to SA, GA, JA, and IAA treatments. Notably, , , , and were significantly upregulated under different hormone treatments. Among them, the upregulation of was the most significant. These findings establish a foundation for further functional characterization of and provide theoretical support for their potential applications in apple genetic improvement and agricultural production.