Abstract

Cytoplasmic incompatibility is a selfish reproductive manipulation induced by the endosymbiont Wolbachia in arthropods. In males Wolbachia modifies sperm, leading to embryonic mortality in crosses with Wolbachia-free females. In females, Wolbachia rescues the cross and allows development to proceed normally. This provides a reproductive advantage to infected females, allowing the maternally transmitted symbiont to spread rapidly through host populations. We identified homologs of the genes underlying this phenotype, cifA and cifB, in 52 of 71 new and published Wolbachia genome sequences. They are strongly associated with cytoplasmic incompatibility. There are up to seven copies of the genes in each genome, and phylogenetic analysis shows that Wolbachia frequently acquires new copies due to pervasive horizontal transfer between strains. In many cases, the genes have subsequently acquired loss-of-function mutations to become pseudogenes. As predicted by theory, this tends to occur first in cifB, whose sole function is to modify sperm, and then in cifA, which is required to rescue the cross in females. Although cif genes recombine, recombination is largely restricted to closely related homologs. This is predicted under a model of coevolution between sperm modification and embryonic rescue, where recombination between distantly related pairs of genes would create a self-incompatible strain. Together, these patterns of gene gain, loss, and recombination support evolutionary models of cytoplasmic incompatibility.

中文翻译：

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自私基因的生与死：比较基因组学揭示了细胞质不相容的动态演化。

 抽象的

细胞质不相容是节肢动物中内共生沃尔巴克氏体引起的一种自私生殖操作。在雄性中，沃尔巴克氏体会改变精子，导致与不含沃尔巴克氏体的雌性杂交时胚胎死亡。在雌性中，沃尔巴克氏体拯救了杂交并使发育正常进行。这为受感染的雌性提供了生殖优势，使母体传播的共生体能够在宿主群体中快速传播。我们在 71 个新发表的沃尔巴克氏体基因组序列中的 52 个中鉴定出了该表型背后的基因cifA和cifB的同源物。它们与细胞质不相容性密切相关。每个基因组中有多达七个基因拷贝，系统发育分析表明，由于菌株之间普遍的水平转移，沃尔巴克氏体经常获得新拷贝。在许多情况下，这些基因随后获得了功能丧失突变，成为假基因。正如理论预测的那样，这种情况往往首先发生在cifB中，其唯一功能是修饰精子，然后发生在cifA中，cifA 是拯救雌性杂交所必需的。尽管cif基因会重组，但重组很大程度上限于密切相关的同源物。这是在精子修饰和胚胎拯救之间的协同进化模型下预测的，其中远缘基因对之间的重组将产生自交不亲和的菌株。总之，这些基因获得、丢失和重组的模式支持细胞质不相容的进化模型。