Molecular Characterization of Two Toll Receptors in and Their Potential Roles in Antibacterial Response.

Tolls/Toll-like receptors (TLRs) play a key role in innate immunity by detecting the invading microbes and subsequently activating downstream signaling cascades. In this study, two new molluscan Toll members (designed as and ) were identified from triangle-shell pearl mussel (). The obtained full-length cDNA was 3207 bp consisting of a 2223 bp open reading frame (ORF) that encoded a peptide of 740 amino acids. cDNA is a 3216 bp molecule that contains an ORF of 2139 bp encoding a protein of 712 amino acids. The deduced and proteins share two common structures: extracellular leucine-rich repeat (LRR) domains and intracellular Toll/interleukin-1 receptor (TIR) domain. Quantitative real-time PCR results showed that and were mainly expressed in the hepatopancreas and the gills, and they responded rapidly to bacterial stimulation. RNA interference by dsRNA results revealed that and RNAi strongly decreased the expression of lysozyme () and defensin () in the gills of RNAi-treated mussels with challenge. As a pattern recognition receptor, the prokaryotic expressed the recombinant LRR domains of and (rHcToll6-LRR and rHcToll7-LRR) could bind to Gram-positive and Gram-negative bacteria and had a strong tendency to recognize lipopolysaccharide (LPS) and peptidoglycan (PNG). rHcToll6-LRR and rHcToll7-LRR exhibited a significant bactericidal activity against and . These findings provide useful information to characterize Tolls in mussels.