Genome-wide characterization of Chrysanthemum indicum TCP genes reveals a positive role for CiTCP23 in salt response tolerance

The teosinte branched1, cycloidea, and proliferating cell factor family (TCP) proteins are plant-specific transcription factors that play crucial roles in regulating plant development and stress responses. However, information on the TCP family in Chrysanthemum indicum is limited. In this study, we identified 35 CiTCP family members and characterized their structural features, phylogenetic relationships, and expression patterns across various tissues and in response to different stress treatments. Phylogenetic analysis classified the CiTCP family members into three distinct subfamilies: PCF, CYC/TB1, and CIN. This classification was corroborated by the exon-intron structures and conserved motifs. Expression level analysis demonstrated that PCF type genes were broadly expressed in different tissues, while most CYC/TB1 and CIN type genes exhibited predominant expression in specific tissues. Most CiTCPs responded to abiotic stress treatments, with their response to salt stress occurring primarily within one hour of exposure. Notably, Arabidopsis plants overexpressing CiTCP23 showed insensitivity to salt stress, as evidenced by higher germination rates, longer seedling roots, and significantly improved salt stress resistance compared to wild-type (WT) plants. Quantitative RT-PCR (qRT-PCR) analysis showed that several salt-responsive genes, such as AtSOS1, AtSOS2, AtSOS3, AtABF3, AtCOR15A, AtADH, AtCBF4, AtRD29A, and AtRD29B, were significantly upregulated in CiTCP23 overexpressing plants. Collectively, these findings suggest that CiTCP23 positively regulates salt tolerance in Arabidopsis by modulating the expression of key genes involved in the salt response.