Abstract
Sessile plants rely on individual cells to perceive pathogens and coordinate defense. Guard cells (GCs), best known for regulating stomatal aperture, have poorly understood intrinsic immune roles. Here, we integrate single-cell and spatial analyses of Arabidopsis thaliana leaves infected with diverse phytopathogens, combining live and fixed imaging of transgenic immune reporters with single cell transcriptomic data. Powdery mildew infection triggers strong salicylic acid (SA) biosynthesis and transport in pavement cells, spreading to neighboring uninfected cells. In contrast, GCs fail to activate SA biosynthesis or SA-responsive genes. These cell-type-specific immune programs distinguishing GC and pavement cells are conserved across infections by the hemibiotrophic fungus Colletotrichum higginsianum and the bacterial pathogen Pseudomonas syringae. Despite impaired SA signaling and response, GCs display rapid calcium influx and pronounced reactive oxygen species bursts, transmitting immune signals to adjacent pavement cells via the apoplast. Notably, GCs are incompatible with adapted fungal pathogens and underwent hypersensitive cell death. Together, these findings uncover distinct immune programs among epidermal cell types, highlight GC-autonomous defense mechanisms, and provide a framework for understanding spatial immune coordination in plants.
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All constructs and transgenic lines generated in this study are available from the corresponding author upon request. Source data are provided with this paper.
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Acknowledgments
We thank ABRC and NASC for providing the mutant seeds and reporter lines used in this study. We also thank Dr. Chris Ambrose for providing the DM398 seeds. This work was supported by grants from the Natural Science and Engineering Research Council of Canada (Discovery Grant) and the Diverse Field Crop Cluster: Agriculture and Agri-Food Canada to Y.W.
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Y.W. and J.S. conceived and coordinated the study; Y.W. and J.S. designed the experiments. J.S. and M.M. conducted plant transformation and transgenic line screening. D.K. and W.A. maintained powdery mildews and performed pathogen inoculation. J.S. conducted microscopy and imaging; J.S., M.M., and Y.W. conducted data analyses. J.S. and Y.W. wrote the manuscript. J.S., Y.C., and Y.W. revised the manuscript and were involved in the discussion of the work.
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Song, J., Modareszadeh, M., Kumarapeli, D. et al. Cell-type-specific immune programs orchestrate spatial defense in the Arabidopsis leaf epidermis. Nat Commun (2026). https://doi.org/10.1038/s41467-026-70843-z
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DOI: https://doi.org/10.1038/s41467-026-70843-z
