Two host clades, two bacterial arsenals: evolution through gene losses in facultative endosymbionts.
Two host clades, two bacterial arsenals: evolution through gene losses in facultative endosymbionts.
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DOI：
10.1093/gbe/evv030
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发表时间：
2015-02-20
影响因子：
3.3
通讯作者：
Mouton L
中科院分区：
文献类型：
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作者：
Rollat-Farnier PA;Santos-Garcia D;Rao Q;Sagot MF;Silva FJ;Henri H;Zchori-Fein E;Latorre A;Moya A;Barbe V;Liu SS;Wang XW;Vavre F;Mouton L
细菌内共生是昆虫重要的进化过程，其中既有专性共生体，也有兼性共生体。这些共生体的进化是由进化趋同驱动的，它们是原核生物中最小的基因组之一。兼性共生体的大宿主谱和它们用于感染新宿主的策略的高度多样性可能影响它们的基因组的进化，并解释了为什么它们比专性共生体经历更少的基因组侵蚀。由于细菌在昆虫的两个进化枝中具有特定的关系，因此，防御汉米尔顿菌适合于兼性共生体基因组进化的研究。在蚜虫中，H.在几个物种中发现了防御素，具有中等流行率，并提供对拟寄生物的保护。在粉虱中，H. defensa在某些烟粉虱物种中几乎是固定的，这表明了专性共生的重要作用和向专性共生的转变。本研究对H.两个B中存在防御。烟粉虱物种（中东小亚细亚1和地中海）和蚜虫Acyrthosiphon豌豆揭示，他们属于两个不同的分支，并经历了特定的基因丢失。在蚜虫中，它含有高毒性因子，可以进行保护和水平转移。在粉虱中，基因组失去了这些因子，似乎获得基因的能力有限。然而，它含有可能参与生产必需营养素的基因，这与这种共生体的原始作用一致。总之，虽然H.防御菌与其宿主之间存在互惠互动，它们的基因组遵循不同的进化轨迹，反映了它们的表型，并可能对它们的进化性产生重要影响。
Bacterial endosymbiosis is an important evolutionary process in insects, which can harbor both obligate and facultative symbionts. The evolution of these symbionts is driven by evolutionary convergence, and they exhibit among the tiniest genomes in prokaryotes. The large host spectrum of facultative symbionts and the high diversity of strategies they use to infect new hosts probably impact the evolution of their genome and explain why they undergo less severe genomic erosion than obligate symbionts. Candidatus Hamiltonella defensa is suitable for the investigation of the genomic evolution of facultative symbionts because the bacteria are engaged in specific relationships in two clades of insects. In aphids, H. defensa is found in several species with an intermediate prevalence and confers protection against parasitoids. In whiteflies, H. defensa is almost fixed in some species of Bemisia tabaci, which suggests an important role of and a transition toward obligate symbiosis. In this study, comparisons of the genome of H. defensa present in two B. tabaci species (Middle East Asia Minor 1 and Mediterranean) and in the aphid Acyrthosiphon pisum revealed that they belong to two distinct clades and underwent specific gene losses. In aphids, it contains highly virulent factors that could allow protection and horizontal transfers. In whiteflies, the genome lost these factors and seems to have a limited ability to acquire genes. However it contains genes that could be involved in the production of essential nutrients, which is consistent with a primordial role for this symbiont. In conclusion, although both lineages of H. defensa have mutualistic interactions with their hosts, their genomes follow distinct evolutionary trajectories that reflect their phenotype and could have important consequences on their evolvability.