Abstract
Piscirickettsia salmonis is one of the most significant pathogens affecting salmon farming. Besides liver, head kidney and spleen, skeletal muscle has shown transcriptional immune responses to these bacteria, but the contribution of non-coding RNAs remains poorly understood. This study investigates the role of long non-coding RNAs (lncRNAs) in the immune response of rainbow trout skeletal muscle and primary myotube cultures infected with P. salmonis. Using RNA-seq data from both in vivo and in vitro muscle under control and infected conditions, the analysis identified 4263 candidate lncRNAs through a stringent bioinformatics pipeline. These lncRNAs were mostly classified as exonic and intergenic, showing distinct genomic distributions and structural differences depending on the source. Expression analyses revealed that cell type had a stronger effect on lncRNA profiles than infection status. From 764 differentially expressed lncRNAs, 191 were uniquely associated with infected and 180 with control conditions, mainly unannotated. Functional predictions based on co-expression and proximity to coding genes suggest that lncRNAs are primarily involved in downregulation of structural-cellular maintenance under control conditions, whereas during infection, they are related to immunity, signaling, and apoptosis. Overall, the findings indicate that lncRNAs exhibit origin-specific regulatory roles and are modulated by P. salmonis infection, highlighting their potential importance in fish immune responses.