The natural diversity of pathogen effectors and host immune components represents a snapshot of the underlying evolutionary processes driving the host-pathogen arms race. In plants, this arms race is manifested by an ongoing cycle of disease and resistance driven by pathogenic effectors that promote disease (effector-triggered susceptibility; ETS) and plant resistance proteins that recognize effector activity to trigger immunity (effector-triggered immunity; ETI). Here we discuss how this ongoing ETS-ETI cycle has shaped the natural diversity of both plant resistance proteins and pathogen effectors. We focus on the evolutionary forces that drive the diversification of the molecules that determine the outcome of plant-pathogen interactions and introduce the concept of metapopulation dynamics (i.e., the introduction of genetic variation from conspecific organisms in different populations) as an alternative mechanism that can introduce and maintain diversity in both host and pathogen populations.

病原体效应物和宿主免疫成分的自然多样性代表了驱动宿主-病原体军备竞赛的潜在进化过程的快照。在植物中，这种军备竞赛的表现是由促进疾病的病原效应物（效应物触发的易感性；ETS）和识别效应物活性以触发免疫的植物抗性蛋白（效应物触发的免疫性；ETI）驱动的疾病和抗性的持续循环. 在这里，我们讨论了这个正在进行的 ETS-ETI 循环如何塑造植物抗性蛋白和病原体效应物的自然多样性。我们专注于推动决定植物-病原体相互作用结果的分子多样化的进化力量，并引入了元种群动力学的概念（即，