Department of Integrative Biology, University of California, Berkeley, Berkeley, California, 94720.
Evolution. 2019 Dec;73(12):2461-2475. doi: 10.1111/evo.13833. Epub 2019 Sep 3.
The evolution of resistance to parasites is fundamentally important to disease ecology, yet we remain unable to predict when and how resistance will evolve. This is largely due to the context-dependent nature of host-parasite interactions, as the benefit of resistance will depend on the abiotic and biotic environment. Through experimental evolution of the plant pathogenic bacterium Pseudomonas syringae and two lytic bacteriophages across two different environments (high-nutrient media and the tomato leaf apoplast), we demonstrate that de novo evolution of resistance is negligible in planta despite high levels of resistance evolution in vitro. We find no evidence supporting the evolution of phage-selected resistance in planta despite multiple passaging experiments, multiple assays for resistance, and high multiplicities of infection. Additionally, we find that phage-resistant mutants (evolved in vitro) did not realize a fitness benefit over phage-sensitive cells when grown in planta in the presence of phage, despite reduced growth of sensitive cells, evidence of phage replication in planta, and a large fitness benefit in the presence of phage observed in vitro. Thus, this context-dependent benefit of phage resistance led to different evolutionary outcomes across environments. These results underscore the importance of studying the evolution of parasite resistance in ecologically relevant environments.
寄生虫抗性的进化对疾病生态学至关重要，但我们仍然无法预测抗性何时以及如何进化。这主要是由于宿主-寄生虫相互作用的上下文依赖性，因为抗性的好处将取决于非生物和生物环境。通过在两个不同环境（高营养培养基和番茄叶片质外体）中对植物病原细菌丁香假单胞菌和两种裂解噬菌体进行实验进化，我们证明尽管在体外有高水平的抗性进化，但在植物体内几乎没有新的抗性进化。尽管进行了多次传代实验、多次抗性检测以及高感染倍数，我们仍未发现支持噬菌体选择抗性在植物体内进化的证据。此外，我们发现，当噬菌体存在时，在植物体内生长时，噬菌体抗性突变体（在体外进化）并没有比噬菌体敏感细胞获得更多的适应性益处，尽管敏感细胞的生长受到抑制，噬菌体在植物体内复制的证据以及在体外观察到的噬菌体存在时的巨大适应性益处。因此，这种依赖于上下文的噬菌体抗性益处导致了不同环境下的不同进化结果。这些结果强调了在生态相关环境中研究寄生虫抗性进化的重要性。
