All cellular life forms are afflicted by diverse genetic parasites, including viruses and other types of mobile genetic elements (MGEs), and have evolved multiple, diverse defence systems that protect them from MGE assault via different mechanisms. Here, we provide our perspectives on how recent evidence points to tight evolutionary connections between MGEs and defence systems that reach far beyond the proverbial arms race. Defence systems incur a fitness cost for the hosts; therefore, at least in prokaryotes, horizontal mobility of defence systems, mediated primarily by MGEs, is essential for their persistence. Moreover, defence systems themselves possess certain features of selfish elements. Common components of MGEs, such as site-specific nucleases, are 'guns for hire' that can also function as parts of defence mechanisms and are often shuttled between MGEs and defence systems. Thus, evolutionary and molecular factors converge to mould the multifaceted, inextricable connection between MGEs and anti-MGE defence systems.

中文翻译：

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遗传基因和宿主防御系统的进化纠缠：租用枪支。

所有细胞生命形式都受到多种遗传寄生虫的折磨，包括病毒和其他类型的移动遗传元件（MGE），并且已经进化出多种多样的防御系统，可以通过不同的机制保护它们免受MGE的攻击。在这里，我们提供观点，说明最近的证据如何表明MGE与防御系统之间紧密的进化联系，而这种联系远不只是众所周知的军备竞赛。防御系统会给主机带来一定的健身费用；因此，至少在原核生物中，主要由MGE介导的防御系统的水平机动性对其持久性至关重要。而且，防御系统本身具有自私要素的某些特征。MGE的常见组成部分，例如位点特异性核酸酶，是“租用枪支” 它也可以作为防御机制的一部分，通常在MGE和防御系统之间穿梭。因此，进化和分子因素汇聚在一起，塑造了MGE和反MGE防御系统之间多方面的，密不可分的联系。