BACKGROUND Toll-like receptors (TLRs) are the most widely studied innate immunity receptors responsible for recognition of invading pathogens. Among the TLR family, TLR5 is the only that senses and recognizes flagellin, the major protein of bacterial flagella. TLR5 has been reported to be under overall purifying selection in mammals, with a small proportion of codons under positive selection. However, the variation of substitution rates among major mammalian groups has been neglected. Here, we studied the evolution of TLR5 in mammals, comparing the substitution rates among groups. RESULTS In this study we analysed the TLR5 substitution rates in Euungulata, Carnivora, Chiroptera, Primata, Rodentia and Lagomorpha, groups. For that, Tajima's relative rate test, Bayesian inference of evolutionary rates and genetic distances were estimated with CODEML's branch model and RELAX. The combined results showed that in the Lagomorpha, Rodentia, Carnivora and Chiroptera lineages TLR5 is evolving at a higher substitution rate. The RELAX analysis further suggested a significant relaxation of selective pressures for the Lagomorpha (K = 0.22, p < 0.01), Rodentia (K = 0.58, p < 0.01) and Chiroptera (K = 0.65, p < 0.01) lineages and for the Carnivora ancestral branches (K = 0.13, p < 0.01). CONCLUSIONS Our results show that the TLR5 substitution rate is not uniform among mammals. In fact, among the different mammal groups studied, the Lagomorpha, Rodentia, Carnivora and Chiroptera are evolving faster. This evolutionary pattern could be explained by 1) the acquisition of new functions of TLR5 in the groups with higher substitution rate, i.e. TLR5 neofunctionalization, 2) by the beginning of a TLR5 pseudogenization in these groups due to some redundancy between the TLRs genes, or 3) an arms race between TLR5 and species-specific parasites.

中文翻译：

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对替代率的分析表明，在哺乳动物群体中，TLR5的进化速率不同。

背景技术Toll样受体（TLR）是负责识别入侵病原体的最广泛研究的先天免疫受体。在TLR家族中，TLR5是唯一能感知和识别鞭毛蛋白的细菌，鞭毛蛋白是细菌鞭毛的主要蛋白质。据报道，在哺乳动物中TLR5处于整体纯化选择之下，一小部分密码子处于阳性选择之下。但是，主要哺乳动物群体之间的替代率差异已被忽略。在这里，我们研究了哺乳动物中TLR5的进化，比较了各组之间的替代率。结果在这项研究中，我们分析了Euungulata，Carnivora，Chiroptera，Primata，Rodentia和Lagomorpha组中的TLR5替代率。为此，田岛的相对比率测试 用CODEML的分支模型和RELAX估计进化速率和遗传距离的贝叶斯推断。综合结果表明，在Lagomorpha，Rodentia，Carnivora和Chiroptera世系中，TLR5的进化替代率更高。RELAX分析进一步表明，Lagomorpha（K = 0.22，p <0.01），Rodentia（K = 0.58，p <0.01）和Chiroptera（K = 0.65，p <0.01）以及食肉动物的选择性压力显着降低。祖先的分支（K = 0.13，p <0.01）。结论我们的研究结果表明，哺乳动物之间TLR5的替代率不一致。实际上，在所研究的不同哺乳动物群体中，Lagomorpha，Rodentia，Carnivora和Chiroptera的进化速度更快。