Genome-wide characterization of the Toll-like receptor gene family in Triplophysa rosa and expression profiles in response to Aeromonas hydrophila infection

Abstract

Toll-like receptors (TLRs) are key pattern recognition receptors playing a pivotal role in innate immunity against pathogen invasion. Although numerous studies have clarified the characteristics and functions of TLRs in both invertebrates and vertebrates, little information is available about TLR genes in the cavefish Triplophysa rosa. Hence, 16 TLR family members, including several fish-specific TLRs (TLR18, TLR19, TLR20, and TLR21), were identified and characterized based on the T. rosa genome. Phylogenetic analysis showed that these TLR genes could be classified into six subfamilies, namely TLR1, TLR3, TLR4, TLR5, TLR7, and TLR11, revealing their evolutionary conservation together with structural analysis. By examining gene copy numbers of TLR genes from several fish species, gene duplications and losses were observed. Moreover, the expression patterns of TLR genes in the gill, skin, intestine, and liver of healthy T. rosa, as well as those in the gill and intestine, in response to Aeromonas hydrophila infection, were investigated by qPCR. Results revealed that 16 TLR genes were ubiquitously expressed in all tested tissues. Furthermore, the expression of most TLRs, including TrTLR4.1, TrTLR4.2, TrTLR5.1, TrTLR9, TrTLR18, TrTLR19, and TrTLR20, was upregulated at all time points. Most TLRs in mucosal immune organs significantly responded to A. hydrophila infection, indicating that the differential expression of TLRs plays important roles in mediating innate immune responses for host defense. Collectively, our findings might help elucidate the crucial roles of TLRs in the immune response of T. rosa, providing valuable genomic resources for future studies investigating the innate immune mechanisms underlying host defense against pathogen infection.