Comparative genomics reveals high rates of horizontal transfer and strong purifying selection on rhizobial symbiosis genes
Comparative genomics reveals high rates of horizontal transfer and strong purifying selection on rhizobial symbiosis genes
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DOI：
10.1098/rspb.2020.1804
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发表时间：
2021-01-13
影响因子：
4.7
通讯作者：
Tiffin，Peter
中科院分区：
文献类型：
--
作者：
Epstein，Brendan;Tiffin，Peter
水平转移（HT）改变了根瘤菌基因组中的共生基因库，并可能在根瘤菌-豆科植物共生的持续进化中发挥重要作用。为了深入了解不同功能作用（结瘤、固氮、寄主效益和根瘤菌适应性）的共生基因的HT程度，我们对27个根瘤菌基因组的全基因组序列进行了比较基因组和选择分析。我们发现共生基因在根瘤菌谱系中具有较高的HT率，但也具有净化选择的特征（低Ka: Ks）。高温疗法和净化选择似乎在参与启动共生（如结瘤）的基因和在为宿主提供中介利益的全基因组关联候选基因中特别强。这些模式与根瘤菌通过共生基因的丧失和获得来适应宿主环境是一致的，但与宿主施加的正选择通过反复的正选择来驱动共生基因的分化是不一致的。
Horizontal transfer (HT) alters the repertoire of symbiosis genes in rhizobial genomes and may play an important role in the on-going evolution of the rhizobia–legume symbiosis. To gain insight into the extent of HT of symbiosis genes with different functional roles (nodulation, N-fixation, host benefit and rhizobial fitness), we conducted comparative genomic and selection analyses of the full-genome sequences from 27 rhizobial genomes. We find that symbiosis genes experience high rates of HT among rhizobial lineages but also bear signatures of purifying selection (low Ka : Ks). HT and purifying selection appear to be particularly strong in genes involved in initiating the symbiosis (e.g. nodulation) and in genome-wide association candidates for mediating benefits provided to the host. These patterns are consistent with rhizobia adapting to the host environment through the loss and gain of symbiosis genes, but not with host-imposed positive selection driving divergence of symbiosis genes through recurring bouts of positive selection.