AUTHOR=Huang Ying , Zhang Guosong , Ren Qian 

TITLE=Molecular Characterization of Two Toll Receptors in Hyriopsis cumingii and Their Potential Roles in Antibacterial Response

JOURNAL=Frontiers in Physiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2019.00952

DOI=10.3389/fphys.2019.00952

ISSN=1664-042X

ABSTRACT=<p>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 <italic>HcToll6</italic> and <italic>HcToll7</italic>) were identified from triangle-shell pearl mussel (<italic>Hyriopsis cumingii</italic>). The obtained <italic>HcToll6</italic> full-length cDNA was 3207 bp consisting of a 2223 bp open reading frame (ORF) that encoded a peptide of 740 amino acids. <italic>HcToll7</italic> cDNA is a 3216 bp molecule that contains an ORF of 2139 bp encoding a protein of 712 amino acids. The deduced <italic>HcToll6</italic> and <italic>HcToll7</italic> 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 <italic>HcToll6</italic> and <italic>HcToll7</italic> were mainly expressed in the hepatopancreas and the gills, and they responded rapidly to bacterial stimulation. RNA interference by dsRNA results revealed that <italic>HcToll6</italic> and <italic>HcToll7</italic> RNAi strongly decreased the expression of lysozyme (<italic>HcLyso</italic>) and defensin (<italic>HcDef</italic>) in the gills of RNAi-treated mussels with <italic>Vibrio parahaemolyticus</italic> challenge. As a pattern recognition receptor, the prokaryotic expressed the recombinant LRR domains of <italic>HcToll6</italic> and <italic>HcToll7</italic> (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 <italic>in vitro</italic> bactericidal activity against <italic>V. parahaemolyticus</italic> and <italic>Staphylococcus aureus</italic>. These findings provide useful information to characterize Tolls in mussels.</p>