Abstract:Portunus trituberculatus, an economically important food species in China, lacks adaptive immunity and can induce effective immune responses to resist pathogen via innate immunity. Toll-like receptors as pattern recognition receptors (PRRs) play crucial role in innate immune responses. The current study found a novel Toll gene named as PtToll4 from P. trituberculatus by rapid amplification of cDNA ends (RACE) technique. The full-length cDNA of PtToll4 was 4276 bp, which contains an open reading frame (ORF) of 2685 bp, a 3¢ untranslated region (UTR) of 1252 bp, and a 5¢ UTR of 339 bp. The ORF encoded a polypeptide of 895 amino acids with a predicted molecular weight of 102.5 kDa. PtToll4 is a transmembrane protein that contains several common structural domains of TLRs, such as LRR, LRRCT motif in the extracellular domain and a TIR domain in the intracellular region. The BLAST analysis showed that PtToll4 shared the highest homology with Eriocheir sinensis Toll2. PtToll4 was widely expressed in hemocyte, heart, gill, hepatopancreas, stomach, intestine, muscle, cuticle, and eyestalk, and mainly distributed in the hemocyte and cuticle. A weak expression level was detected in the hepatopancreas. WSSV inflection significantly induced PtToll4 expression in hemocyte at 6 h, and V. parahemolyticus inflection had a little effect on it only at 48 h. Low salinity reduced PtToll4 expression. Our results suggested that PtToll4 may play an important role in innate immune of P. trituberculatus and would provide useful information for the research of immunity regulation in crustaceans.
