Different genetic patterns in avian Toll-like receptor (TLR)5 genes

Toll-like receptors (TLRs) mediate immune response via recognition of pathogen-associated molecular patterns (PAMPs), thus play important roles in host defense. Polymorphisms of TLR5 may affect their recognition of bacterial flagellin, leading to varied host resistance to pathogenic infections. Here, we cloned TLR5 genes from Common Pheasant, Guinea fowl and 9 Chicken breeds and analyzed their sequences. The open reading frames of TLR5 were sequenced. Amino acid analysis indicated that TLR5 from Chicken breeds shared 99.4-99.9% homology. The amino acid homology of TLR5 ranged from 92.1 to 92.5% between Chickens and Guinea fowl, 95.7-96.1% between Chickens and Turkey, 94.3-94.7% between Chickens and Common Pheasant, and 79.9-80.1% between Chickens and Zebra-finch. Different genetic patterns were determined among Chickens, Common Pheasant, Guinea fowl, Turkey and Zebra-finch. It was found that there were 92 amino acid polymorphic sites, among which 5 sites in chicken TLR5, 63 sites in Guinea fowl TLR5 and 44 sites in Common Pheasant TLR5. Our data indicate that the positive Darwinian selection occurred in avian TLR5 genes since frequency of non-synonymous (d ( N )) > frequency of synonymous (d ( S )). These results also demonstrate that avian TLR5 genes are polymorphic among avian breeds, suggesting a varied resistance among breeds of avian. This information might be of help to improve the health of avian by breeding and vaccination.