BACKGROUND Mutator-like elements (MULEs) are a significant superfamily of DNA transposons on account of their: (i) great transpositional activity and propensity for insertion in or near gene sequences, (ii) their consequent high mutagenic capacity, and, (iii) their tendency to acquire host gene fragments. Consequently, MULEs are important genetic tools and represent a key study system for research into host-transposon interactions. Yet, while several studies have focused on the impacts of MULEs on crop and fungus genomes, their evolution remains poorly explored. RESULTS We perform comprehensive bioinformatic and phylogenetic analyses to address currently available MULE diversity and reconstruct evolution for the group. For this, we mine MULEs from online databases, and combine search results with available transposase sequences retrieved from previously published studies. Our analyses uncover two entirely new MULE clades that contain elements almost entirely restricted to arthropod hosts, considerably expanding the set of MULEs known from this group, suggesting that many additional MULEs may await discovery from further arthropod genomes. In several cases, close relationships occur between MULEs recovered from distantly related host organisms, suggesting that horizontal transfer events may have played an important role in the evolution of the group. However, it is apparent that MULEs from plants remain separate from MULEs identified from other host groups. MULE structure varies considerably across phylogeny, and TIR length is shown to vary greatly both within and between MULE groups. Our phylogeny suggests that MULE diversity is clustered in well-supported groups, typically according to host taxonomy. With reference to this, we make suggestions on how MULE diversity can be partitioned to provide a robust taxonomic framework. CONCLUSIONS Our study represents a considerable advance in the understanding of MULE diversity, host range and evolution, and provides a taxonomic framework for the classification of further MULE elements that await discovery. Our findings also raise a number of questions relating to MULE biology, suggesting that this group will provide a rich avenue for future study.

中文翻译：

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Mutator 转座因子在真核生物多样性中的进化。

背景 突变体样元件 (MULE) 是 DNA 转座子的一个重要超家族，因为它们：(i) 巨大的转座活性和插入基因序列中或附近的倾向，(ii) 它们随之而来的高诱变能力，以及，(iii)他们倾向于获得宿主基因片段。因此，MULE 是重要的遗传工具，代表了研究宿主-转座子相互作用的关键研究系统。然而，虽然有几项研究集中在 MULE 对作物和真菌基因组的影响，但它们的进化仍然缺乏探索。结果 我们进行了全面的生物信息学和系统发育分析，以解决当前可用的 MULE 多样性并重建该组的进化。为此，我们从在线数据库中挖掘 MULE，并将搜索结果与从先前发表的研究中检索到的可用转座酶序列相结合。我们的分析揭示了两个全新的 MULE 进化枝，其中包含几乎完全限于节肢动物宿主的元素，大大扩展了该组已知的 MULE 集合，这表明许多额外的 MULE 可能等待从进一步的节肢动物基因组中发现。在某些情况下，从远缘宿主生物中恢复的 MULE 之间存在密切关系，这表明水平转移事件可能在该群体的进化中发挥了重要作用。然而，很明显，来自植物的 MULE 与从其他宿主群体中识别的 MULE 是分开的。MULE 结构在系统发育中差异很大，并且 TIR 长度显示在 MULE 组内和组之间变化很大。我们的系统发育表明 MULE 多样性聚集在得到良好支持的群体中，通常根据宿主分类。参考这一点，我们就如何划分 MULE 多样性以提供稳健的分类框架提出建议。结论 我们的研究代表了在理解 MULE 多样性、宿主范围和进化方面取得了相当大的进步，并为等待发现的进一步 MULE 元素的分类提供了分类框架。我们的研究结果还提出了一些与 MULE 生物学相关的问题，表明该小组将为未来的研究提供丰富的途径。结论 我们的研究代表了在理解 MULE 多样性、宿主范围和进化方面取得了相当大的进步，并为等待发现的进一步 MULE 元素的分类提供了分类框架。我们的研究结果还提出了一些与 MULE 生物学相关的问题，表明该小组将为未来的研究提供丰富的途径。结论 我们的研究代表了在理解 MULE 多样性、宿主范围和进化方面取得了相当大的进步，并为等待发现的进一步 MULE 元素的分类提供了分类框架。我们的研究结果还提出了一些与 MULE 生物学相关的问题，表明该小组将为未来的研究提供丰富的途径。