Systematic identification and characterization of nine interferon regulatory factor (IRF) genes in spotted sea bass (Lateolabrax maculatus) reveals teleost-specific expansions and pathogen-responsive specialization

Interferon regulatory factors (IRFs) are essential transcriptional regulators of teleost innate immunity. In this study, nine IRF genes (IRF4a, IRF4b, IRF5, IRF6, IRF7, IRF8, IRF9, IRF10, and IRF11) were identified and characterized in the economically important spotted sea bass ( Lateolabrax maculatus ). Bioinformatic analysis revealed that all proteins except IRF11 possess a conserved DNA-binding domain (DBD) containing characteristic tryptophan repeats, along with a C-terminal IRF association domain (IAD). In contrast, IRF11 only contains the DBD and lacks a canonical IAD. Phylogenetic and synteny analyses supported their orthology and classification within the teleost IRF family. Under basal conditions, all nine genes were constitutively expressed across tested tissues, with highest expression in spleen or gills. Following immune challenge with LPS, Poly (I:C), or Edwardsiella tarda , each IRF exhibited distinct time‑ and tissue‑dependent expression patterns. IRF4a and IRF4b exhibited divergent expression patterns, which suggests functional specialization following gene duplication. IRF6, IRF7, and IRF10 were strongly induced by Poly (I:C), which implicates them in antiviral defense, whereas IRF8 and IRF11 were significantly upregulated in response to bacterial challenge, suggesting a role in antibacterial immunity. IRF9 responded to both stimuli, suggesting broader immunoregulatory functions. This study provides a comprehensive characterization of the specialized and overlapping roles of the IRF family in host defense of spotted sea bass.