Genome-wide identification and characterization of toll-like receptor genes in spotted sea bass (Lateolabrax maculates) and their involvement in the host immune response to Vibrio harveyi infection

Toll-like receptor (TLR) genes are the earliest reported pathogen recognition receptors (PRRs) and have been extensively studied. These genes play pivotal roles in the innate immune defense against pathogen invasion. In this study, a total of 16 tlr genes were identified and characterized in spotted sea bass (Lateolabrax maculatus). The tlr genes of spotted sea bass were classified into five subfamilies (tlr1-subfamily, tlr3-subfamily, tlr5-subfamily, tlr7-subfamily, and tlr1-subfamily) according to the phylogenetic analysis, and their annotations were confirmed by a syntenic analysis. The protein domain analysis indicated that most dr genes had the following three major TLR protein domains: a leucine-rich repeat (LEER) domain, a transmembrane region (TM) and a Toll/interleukin-1 receptor (TER) domain. The tlr genes in spotted sea bass were distributed in 11 of 24 chromosomes. The mRNA expression levels of 16 dr genes in response to Vibrio harveyi infection were quantified in the head kidney. Most genes were downregulated following V. harveyi infection, while only 5 tlr genes, including tlr1-1, tlr2-2, tlr5, and tlr7, were significantly upregulated. Collectively, these results help elucidate the crucial roles of dr genes in the immune response of spotted sea bass and may supply valuable genomic resources for future studies investigating fish disease management.