Bacterial endosymbionts that provide nutrients to hosts often have genomes that are extremely stable in structure and gene content. In contrast, the genome of the endosymbiont Hodgkinia cicadicola has fractured into multiple distinct lineages in some species of the cicada genus Tettigades. To better understand the frequency, timing, and outcomes of Hodgkinia lineage splitting throughout this cicada genus, we sampled cicadas over three field seasons in Chile and performed genomics and microscopy on representative samples. We found that a single ancestral Hodgkinia lineage has split at least six independent times in Tettigades over the last 4 million years, resulting in complexes of between two and six distinct Hodgkinia lineages per host. Individual genomes in these symbiotic complexes differ dramatically in relative abundance, genome size, organization, and gene content. Each Hodgkinia lineage retains a small set of core genes involved in genetic information processing, but the high level of gene loss experienced by all genomes suggests that extensive sharing of gene products among symbiont cells must occur. In total, Hodgkinia complexes that consist of multiple lineages encode nearly complete sets of genes present on the ancestral single lineage and presumably perform the same functions as symbionts that have not undergone splitting. However, differences in the timing of the splits, along with dissimilar gene loss patterns on the resulting genomes, have led to very different outcomes of lineage splitting in extant cicadas.

中文翻译：

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蝉属相互依赖的内共生复合物的多重起源


为宿主提供营养的细菌内共生体通常具有结构和基因内容极其稳定的基因组。相比之下，在蝉属的某些物种中，内共生体蝉的基因组已分裂成多个不同的谱系。为了更好地了解整个蝉属霍奇金虫谱系分裂的频率、时间和结果，我们在智利的三个野外季节对蝉进行了采样，并对代表性样本进行了基因组学和显微镜检查。我们发现，在过去 400 万年里， Tettigades中一个单一的霍奇金氏菌祖先谱系至少分裂了六次独立的时间，导致每个宿主产生了 2 到 6 个不同的霍奇金氏菌谱系的复合体。这些共生复合体中的个体基因组在相对丰度、基因组大小、组织和基因内容方面存在显着差异。每个霍奇金氏菌谱系都保留了一小组参与遗传信息处理的核心基因，但所有基因组经历的高水平基因丢失表明，共生细胞之间必须广泛共享基因产物。总的来说，由多个谱系组成的霍奇金复合体编码了祖先单一谱系上存在的几乎完整的基因组，并且可能执行与未经历分裂的共生体相同的功能。然而，分裂时间的差异，以及由此产生的基因组上不同的基因丢失模式，导致了现存蝉谱系分裂的截然不同的结果。