| Summary: | Calmodulins (CaMs) and Calmodulin-like proteins (CMLs) are vital in plant growth, development, and stress responses. However, CaMs and CMLs have not been fully identified and characterized in brown algae, which has been evolving independently of the well-studied green plant lineage. In this study, whole-genome searches revealed one SjCaM and eight SjCMLs in <i>Saccharina japonica</i>, and one EsCaM and eleven EsCMLs in <i>Ectocarpus</i> sp. SjCaM and EsCaM encoded identical protein products and shared 88.59–89.93% amino acid identities with <i>Arabidopsis thaliana</i> AtCaMs, thereby indicating that brown algae CaMs retained a similar Ca<sup>2+</sup> sensors function as in plants. The phylogenetic and gene structure analysis results showed that there was significant divergence in the gene sequences among brown algae CMLs. Furthermore, evolutionary analysis indicated that the function of brown alga CMLs was relatively conserved, which may be related to the fact that brown algae do not need to face complex environments like terrestrial plants. Regulatory elements prediction and the expression analysis revealed the probable functioning of SjCaM/CML genes in gametophyte development and the stress response in <i>S. japonica</i>. In addition, the SjCaM/SjCMLs interacting proteins and chemicals were preliminarily predicted, suggesting that SjCaM/SjCMLs might play putative roles in Ca<sup>2+</sup>/CaM-mediated growth and development processes and stimulus responses. Therefore, these results will facilitate our understanding of the evolution of brown algae CaMs/CMLs and the functional identification of SjCaM/SjCMLs.
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