Expanded threshold of plant immunity by beneficial microbes

Plants have evolved two primary innate immune strategies, pattern-triggered immunity and effector-triggered immunity, to prevent excessive microbial infection. As the 'second genome' of plants, microbiota also regulates the plant growth-immune tradeoff. In this opinion article, we propose that beneficial microbes expand the plant immune threshold by coordinately regulating above-ground and below-ground immune signaling. We integrate this concept into the existing framework of plant immune strategies to construct a novel model of plant immunity. Building upon this foundation, we introduce a novel perspective regarding dose-dependent immune responses. We propose that, in natural systems, non-pathogen-plant interactions should be evaluated not only based on the specific recognition of microbe-associated molecular patterns (MAMPs) but also by incorporating the dose-dependent effects of MAMPs into the assessment framework.