Labeo rohita, Interferon regulatory factor, Innate immunity, PAMPs, A. hydrophila, E. tarda, Microbiology, QR1-502, Veterinary medicine, SF600-1100

Immune response to viral infection involves the intricate regulation of type I interferons (IFNs) and interferon-stimulated genes (ISGs) controlled by the interferon regulatory factors (IRFs). Although IFN signaling and the role of IRFs in its regulation have been considerably researched in higher vertebrates, their influence on piscine immunity remains largely unexplained. This article describes the cloning, characterization, and 3D modeling, of Labeo rohita IRF9 (LrIRF9) in depicting the presence of highly conserved DNA-binding domain (DBD) and IRF3-transactivation domains. In the DBD, the predicted nucleotide-binding residues include H44, R83, R85, C86 and N89, while peptide binding residues in the IRF3-transactivation domain involve Y243, K288, L289, L290, M293, K294, Q313, G314, F317, and K330. Phylogenetically, LrIRF9 is evolutionarily close to IRF9 of Cyprinus carpio (93.5 %), Ctenopharyngodon idella (88.2 %) and Mylopharyngodon piceus (88 %). The LrIRF9 gene is expressed in all examined organs, with notably higher levels detected in the intestine, skin, and blood compared to other tissues. In-vitro and in-vivo stimulation with poly I: C or LPS significantly (p < 0.05) enhanced LrIRF9 gene expression in most of the examined tissues, RBCs, PBLs, and macrophages. In response to Aeromonas hydrophila and Edwardsiella tarda infection, LrIRF9 gene expression was also enhanced in some of the tested organs/tissues. Collectively, these data provide a critical insight into the piscine IRF9 during pathogenic insults.