Variation in positive selection in termite GNBPs and relish
Variation in positive selection in termite GNBPs and relish
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DOI：
10.1093/molbev/msj037
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发表时间：
2006-02-01
影响因子：
10.7
通讯作者：
Crozier, RH
中科院分区：
文献类型：
--
作者：
Bulmer, MS;Crozier, RH
群居昆虫是研究先天免疫系统分子进化的模式生物。它们的多样性提供了密切相关物种之间的比较分析，群体生活可能有助于对免疫系统施加病原体压力。本文采用不同的非同义位点（氨基酸改变）和同义位点（沉默位点）核苷酸替换模型，比较了13种澳大利亚白蚁（Nasutitermes）三种免疫基因的不同选择水平和类型。免疫基因包括两个编码病原体识别蛋白（革兰氏阴性细菌结合蛋白），它们在白蚁进化之前或之后不久复制和分化，以及一个转录因子（穗），它诱导抗菌肽的产生。将四种不受限制的dN/dS（非同义取代率与同义取代率之比）分配给不同的准子代谱系的进化模型进行比较，发现正向选择（dN/dS bbb1）的发生在不同的谱系和三个基因之间是不同的。正选择似乎推动了三个地下白蚁祖先谱系中所有三个基因的进化。此前曾有人提出，白蚁的祖先谱系在形态和生态方面发生了转变，这与白蚁以腐烂的木材为食有关，这种饮食可能使白蚁暴露于真菌和细菌病原体的水平升高。在所有三种基因中，“津津有味”似乎经历了最高水平的选择压力。分子中正向选择的位点位于对其激活很重要的区域，这表明这些位点上的氨基酸取代是对病原体机制的对抗反应，破坏了津津乐道的激活。
Social insects are model organisms for investigating molecular evolution in the innate immune system. Their diversity affords comparative analysis among closely related species, and group living is likely to contribute to the pathogen stress imposed on the immune system. We used different models of nucleotide substitution at nonsynonymous (amino acid altering) and synonymous (silent) sites to compare the different levels and type of selection among three immunity genes in 13 Australian termite species (Nasutitermes). The immunity genes include two encoding pathogen recognition proteins (gram-negative bacterial-binding proteins) that duplicated and diverged before or soon after the evolution of the termites and a transcription factor (Relish), which induces the production of antimicrobial peptides. A comparison of evolutionary models that assign four unrestricted classes of dN/dS (the ratio of the nonsynonymous to synonymous substitution rate) to different Nasutitermes lineages revealed that the occurrence of positive selection (dN/dS > 1) varies among lineages and the three genes. Positive selection appears to have driven the evolution of all three genes in an ancestral lineage of three subterranean termites. It had previously been suggested that there was a transition along this ancestral lineage to termite morphology and ecology associated with a diet of decayed wood, a diet that may expose termites to elevated levels of fungal and bacterial pathogens. Relish appears to have experienced the highest levels of selective pressure for change among all three genes. Positively selected sites in the molecule are located in regions that are important for its activation, which suggests that amino acid substitutions at these sites are a counter response to pathogen mechanisms that disrupt the activation of Relish.