Flagellin Sensing, Signaling, and Immune Responses in Plants.

The flagellin sensing mechanism is one of the most extensively studied topics in plant defense systems. This widespread interest arises from its ability to trigger robust and extensive responses, establishing it as a cornerstone for research into other defense mechanisms. Plants recognize bacterial flagellin epitopes through plasma membrane-localized pattern recognition receptors, initiating pattern-triggered immunity as the front line of defense against bacterial pathogens. In this review, we comprehensively summarize the flagellin sensing mechanisms and signal transduction pathways in plants. We compare flagellin sensing mechanisms between plants and mammals, focusing on epitope processing and recognition. We present detailed downstream signaling events from receptor complex formation to transcriptional reprogramming. Furthermore, we highlight the evolutionary arms race between plants and bacteria and integrate emerging insights into the modulation of flagellin-triggered responses by receptor networking, phytocytokines, and environmental factors. These findings suggest that flagellin-mediated immune responses are highly dynamic and context-dependent. By synthesizing current knowledge with recent discoveries, this review provides updated perspectives on plant-microbe interactions and aims to inspire future research in plant immunity.