Genome-wide profiling of Chrysanthemum indicum BBX gene family and heterologous overexpression of CiBBX13 delays flowering in Arabidopsis

B-box (BBX) proteins are plant-specific zinc-finger proteins, characterized by conserved B-box structural domains, and participate in developmental progression and various stress responses. Nevertheless, genome-wide identification and functional exploration of BBX members in Chrysanthemum indicum ( C. indicum ) have barely been documented. In this work, 23 CiBBX members were retrieved from the C. indicum genome. Phylogenetic clustering divided these members into five subgroups, a classification further validated by comparative analysis of exon-intron arrangements, conserved domain architectures and conserved protein motifs. Promoter cis -element analysis revealed that over 15 CiBBX gene promoters contain numerous cis -regulatory sequences associated with light perception (G-box, BOX4, GT1-motif), phytohormone signaling (ABRE, CGTCA-motif, TGACG-motif) and abiotic stress responses (ARE). Expression profiling showed that numerous CiBBXs were predominantly expressed in leaves and flowers, and were rapidly induced or repressed by short-day (SD) signals. Heterologous overexpression of CiBBX13 (Group IV) in Arabidopsis thaliana resulted in delayed flowering, reduced plant height, and decreased crown width, accompanied by altered expression of several flowering-related genes, including AtCO, AtFT , AtGA20ox2 , and AtFLC . These findings provide evidence from heterologous expression that CiBBX13 potentially modulates multiple flowering-related pathways in Arabidopsis.