Cell-type-specific gating of gene regulatory modules as a hallmark of early immune responses in Arabidopsis leaves.

In plants, multiple cell types contribute to immunity, but what division of labor exists among cell types when immunity is activated? We compared, at single-cell resolution, the response of Arabidopsis thaliana leaf cells during pattern-triggered and effector-triggered immunity (PTI/ETI), sampled at 3 and 5 h after infection with Pseudomonas syringae DC3000. Core defense modules were broadly shared across cell clusters, but their activation varied in timing and intensity, with key immune receptors also showing cell type-specific expression dynamics. Mesophyll cell populations could be distinguished based on their resilience patterns: after the initial response, some populations continue to express defense genes at high levels during both PTI and ETI, while others quickly reinitiate growth-related gene expression programs but only during PTI. Gene regulatory network inference revealed WRKY-regulated modules enriched in cells sensing effectors, while salicylic acid biosynthesis regulators were activated in complementary clusters. Analysis of cue1 mutants demonstrated that core immune responses are robust to altered leaf architecture. In addition, we uncovered cryptic defense pathways, including sucrose-responsive modules, in this mutant. By capturing early immune responses at high resolution, our study reveals cell type-specific coordination of plant immunity and provides a framework for decoding immune signaling networks.