Data from: Host coevolution alters the adaptive landscape of a virus

The origin of new and complex structures and functions is fundamental for shaping the diversity of life. Such key innovations are rare because they require multiple interacting changes. We sought to understand how the adaptive landscape led to an innovation whereby bacteriophage λ evolved the new ability to exploit a receptor, OmpF, on Escherichia coli cells. Previous work showed that this ability evolved repeatedly, despite requiring four mutations in one virus gene. Here, we examine how this innovation evolved by studying six intermediate genotypes of λ isolated during independent transitions to exploit OmpF and comparing them to their ancestor. All six intermediates showed large increases in their adsorption rates on the ancestral host. Improvements in adsorption were offset, in large part, by the evolution of host resistance, which occurred by reduced expression of LamB, the usual receptor for λ. As a consequence of host coevolution, the adaptive landscape of the virus changed such that selection favouring four of the six virus intermediates became stronger after the host evolved resistance, thereby accelerating virus populations along the path to using the new OmpF receptor. This dependency of viral fitness on host genotype thus shows an important role for coevolution in the origin of the new viral function.新结构与新功能的起源是塑造生命多样性的核心基础。这类关键创新极为罕见，因其需要多个相互关联的突变协同发生。本研究旨在解析适应性景观如何推动一项创新的产生——即λ噬菌体（bacteriophage λ）演化出利用大肠杆菌（Escherichia coli）细胞膜上OmpF受体的全新能力。既往研究显示，尽管该功能的演化需要在某一病毒基因中积累4处突变，但这一能力仍可重复演化出现。本研究通过分析6株独立完成向利用OmpF受体过渡的λ噬菌体中间基因型，并与其祖先菌株进行比对，解析了该创新的演化路径。所有6株中间基因型在祖先宿主上的吸附率均大幅提升。然而吸附能力的提升在很大程度上被宿主抗性的演化所抵消：宿主通过降低λ噬菌体的常规受体LamB的表达量获得抗性。由于宿主的协同演化，病毒的适应性景观发生改变——当宿主演化出抗性后，对6株病毒中间基因型中4株的选择压力显著增强，进而加速了病毒种群向使用新型OmpF受体的演化路径推进。综上，病毒适合度对宿主基因型的依赖性，彰显了协同演化在新型病毒功能起源中的关键作用。