Comprehensive Characterization of B-Box Zinc Finger Genes in Citrullus lanatus and Their Response to Hormone and Abiotic Stresses

Plant B-BOX (BBX) zinc finger transcription factors play crucial roles in growth and development and the stress response. Although the BBX family has been characterized in various plants, systematic analysis in watermelon is still lacking. In this study, 25 watermelon genes were identified. ClBBXs were grouped into five clades (Clade I, II, III, IV, and V) based on their conserved domains and phylogenetic relationships. Most of the ClBBXs (84%) might be localized in the nuclei or cytoplasm. The classification of ClBBXs was consistent with their gene structures. They were unevenly distributed in nine chromosomes except for Chr4 and Chr10, with the largest number of six members in Chr2. Segmental duplications were the major factor in family expansion. Some of watermelon and evolved from a common ancestor. In total, 254 hormonal and stress-responsive elements were discovered in promoters. were differentially expressed in tissues, and the expression levels of and were higher in aboveground tissues than in roots, while the patterns of , , , and were the opposite. With salicylic acid, methyl jasmonate and salt stress conditions, 17, 18 and 18 exhibited significant expression changes, respectively. In addition, many , including , and , were also responsive to cold and osmotic stress. In summary, the simultaneous response of multiple to hormonal or abiotic stress suggests that they may have functional interactions in the stress hormone network. Clarifying the roles of key ClBBXs in transcriptional regulation and mediating protein interactions will be an important task. Our comprehensive characterization of the watermelon ClBBX family provides vital clues for the in-depth analysis of their biological functions in stress and hormone signaling pathways.