Genome-wide identification and expression analysis of the actin gene family in soybean (Glycine max).

Actin, one of the most highly conserved and ubiquitous proteins found in all eukaryotes, serves as the primary component of microfilaments. These cytoskeletal elements provide structural support to cells while actively regulating diverse biological processes. Despite the agricultural significance of soybean (Glycine max) as a global legume crop, systematic characterization of its actin gene family remains unexplored. Through comprehensive bioinformatic analysis, we identified 18 soybean actin genes (designated GmACT1-GmACT18) unevenly distributed across 13 of the 20 soybean chromosomes. Phylogenetic analysis classified these genes into five distinct subclasses, with members within each subclass sharing conserved gene structures and protein sequences. All GmACT genes encode predicted polypeptides of 377 amino acids, which display pairwise sequence similarities exceeding 93.10%. Promoter analysis identified many cis-acting elements regulating hormonal and stress responses, underscoring their vital roles in growth and environmental adaptation. Genome synteny analysis identified 29 paralogous GmACT gene pairs, with calculated Ka/Ks ratios (< 0.04) indicating robust purifying selection during gene family expansion. Sequence alignment identified 36 amino acid substitutions among GmACT proteins, including 25 subclass-specific residues that may lead to divergence in biochemical properties. Transcriptome analysis identified distinct spatiotemporal expression patterns, among which GmACT1, 4, 9, 15, and 16 showed consistently high expression not only in all organs and tissues but also under diverse biotic and abiotic stresses, demonstrating their robust and stable expression profile. This constitutive expression suggests these genes are excellent candidates for use as internal controls in gene expression studies. Several GmACT members exhibited stress-responsive expression patterns, implying specialized roles in abiotic/biotic stress adaptation. This systematic investigation establishes fundamental insights into soybean actin genes, laying crucial groundwork for their future functional studies.