Genome-wide Identification and ABA-responsive Characterization of Calmodulin and Calmodulin-like Genes in Salvia miltiorrhiza

Calcium ions (Ca²⁺) are universal secondary messengers that regulate plant growth, development, and responses to environmental stresses. Calmodulin (CaM) and calmodulin-like (CML) proteins are key calcium sensors, yet their roles remain poorly explored in Salvia miltiorrhiza, a traditional medicinal plant. Here, we performed a genome-wide analysis to identify and characterize the CaM and CML gene families in S. miltiorrhiza. We identified six SmCaM genes and twenty-six SmCML genes, revealing conserved EF-hand motifs in SmCaMs, whereas SmCMLs presented significant variability in protein length, domain composition, and gene structure. Phylogenetic analysis classified these proteins into eight subfamilies, suggesting functional divergence. Promoter analysis revealed abundant cis-elements related to light, hormone, and stress responses. Chromosomal mapping indicated nonrandom localization, with significant enrichment in gene-rich regions. Transcriptomic profiling under abscisic acid (ABA) treatment highlighted the stable expression of SmCaMs, whereas SmCMLs presented dynamic, tissue-specific responses. Notably, SmCML19 exhibited root-specific downregulation under ABA stress despite a lack of canonical ABA-responsive elements. These findings provide a comprehensive foundation for understanding the calcium signaling networks in S. miltiorrhiza and may facilitate future studies aiming to increase stress tolerance and secondary metabolite production.