Preliminary Identification and Characterization of Antimicrobial Peptides from the Skin of Rana amurensis Based on Transcriptome Sequencing

The skin of Rana amurensis serves as an important defense barrier against microbial challenges, yet the molecular basis of its cutaneous immune defense and antimicrobial peptide (AMP) repertoire remains incompletely understood. Here, we established a skin transcriptomic profile of R. amurensis following Aeromonas hydrophila infection and integrated transcriptomic and bioinformatic approaches to characterize transcriptional responses and identify candidate AMPs. A total of 1669 differentially expressed genes (DEGs) were identified between the uninfected and infected groups, including 1091 up-regulated and 578 down-regulated genes. Infection with A. hydrophila induced marked transcriptional changes in innate immune-related genes and pathways, including differential expression of genes associated with the Toll-like receptor (TLR) signaling pathway. Transcriptome-based screening identified 151 candidate AMP sequences. Based on sequence characteristics, evolutionary conservation, and physicochemical properties (length ≤50 amino acids and net charge ranging from +2 to +9), six candidates were selected and three randomly selected candidates were chemically synthesized and exhibited antimicrobial activity against bacterial pathogens, inducing less than 10% hemolysis and maintaining L929 cell viability above 79% at 64 μg/mL. These findings indicate that A. hydrophila infection induces coordinated transcriptional responses involving innate immune-related pathways and diverse candidate AMPs in R. amurensis. This study supports the utility of transcriptome-guided discovery for identifying candidate AMPs in amphibians and provides insights into the molecular basis of skin defense in R. amurensis.