Characterization and expression analysis of mitochondrial localization molecule: NOD-like receptor X1 (Nlrx1) in mucosal tissues of turbot (Scophthalmus maximus) following bacterial challenge.

The NOD-like receptor X1 (NLRX1) is a member of highly conserved nucleotide-binding domain (NBD)- and leucine-rich-repeat (LRR)-containing family (known as NLR), that localizes to the mitochondrial outer membrane and regulate the innate immunity by interacting with mitochondrial antiviral-signaling protein (MAVS). As one of cytoplasmic PRRs, NLRX1 plays key roles for pathogen recognition, autophagy and regulating of subsequent immune signaling pathways. In this study, we identified the nlrx1 in turbot as well as its expression profiles in mucosal surfaces following bacterial infection. In our results, the full-length nlrx1 transcript consists of an open reading frame (ORF) of 4,886 bp encoding the putative peptide of 966 amino acids. The phylogenetic analysis revealed the SmNlrx1 showed the closest relationship to Cynoglossus semilaevis. In addition, the Nlrx1 mRNA expression could be detected in all the examined tissues, with the most abundant expression level in head kidney, and the lowest expression level in liver. Moreover, Nlrx1 showed similar expression patterns following Vibrio anguillarum and Streptococcus iniae infection, that were both significantly up-regulated following challenge, especially post S. iniae challenge. Finally, fluorescence microscopy unveiled that the SmNlrx1 localized to mitochondria in HEK293T by N-terminal mitochondrial targeting sequence. Characterization of Nlrx1 might have an important implication in bioenergetic adaptation during metabolic stress, oncogenic transformation and innate immunity and will probably contribute to the development of novel intervention strategies for farming turbot.