Genome-Wide Identification and Characterization of the Calmodulin-Binding Transcription Activators (CAMTA) Gene Family in Brassica U-Triangle Species and Its Potential Role in Response to Phytohormones and Abiotic Stresses

Calmodulin-binding transcription activators (CAMTAs) are pivotal regulators decoding calcium signals, with crucial roles in plant development, hormone responses, and adaptation to abiotic stresses. Although extensive research has been conducted on CAMTAs in model plants such as <i>Arabidopsis thaliana</i>, a comprehensive genome-wide analysis of the CAMTA gene family across the economically important <i>Brassica</i> U-triangle species has not been performed. In this study, we systematically identified and characterized 64 CAMTA genes from the genomes of <i>Brassica</i> U-triangle species. Phylogenetic analysis classified these genes into four conserved groups, a finding corroborated by analyses of gene structure and conserved motifs. These analyses revealed strong evolutionary preservation of functional domains, especially the calmodulin-binding domain (CaMBD). Chromosomal distribution and collinearity assessment highlighted the significant impact of polyploidization on the expansion of the CAMTA family, with most orthologous pairs being under purifying selection. <i>Cis</i>-element analysis in promoters uncovered an abundance of stress- and hormone-related elements, suggesting diverse regulatory roles for these genes. Furthermore, RNA-Seq and RT-qPCR expression profiling demonstrated that <i>BnaCAMTA</i> genes exhibit tissue-specific expression and are dynamically responsive to various phytohormones (ABA, JA, and GA) and abiotic stresses (salt and drought), particularly in the root. Notably, <i>BnaCAMTA5.2</i>, which was prioritized among several validated candidates, mediates the antagonistic regulation of hypocotyl and root growth under GA and salt stress, indicating its key role in balancing growth promotion and stress adaptation. Additionally, we identified a set of stress-related miRNAs that potentially target <i>BnaCAMTAs</i>, suggesting a potential layer of post-transcriptional regulation. Our results provide valuable insights into the evolutionary and functional diversity of CAMTA genes in <i>Brassica</i> U-triangle species and lay a foundation for further research into their roles in enhancing stress resistance in <i>B. napus</i>.