A pair of chitosan receptors confer broad-spectrum fungal resistance.

Chitosan, a major fungal cell wall component, activates plant immunity, yet the underlying perception mechanism remains unknown. In this study, we identified OsFID1, an apoplast-localized DUF26 domain protein, as a chitosan-binding receptor essential for chitosan-triggered immunity. OsFID1 forms a receptor complex with OsFID2, a plasma membrane-localized DUF26 receptor-like kinase, to mediate chitosan sensing and immune activation, requiring OsFID2 phosphorylation for function. The OsFID1-OsFID2 complex confers broad-spectrum resistance to fungal pathogens. OsFID1 homologs are conserved in land plants, which show chitosan-binding activity in both monocots and dicots. Ectopic expression of OsFID1 in wheat and maize enhanced fungal resistance without growth penalty. These findings uncover a conserved receptor complex for direct chitosan sensing, advancing our understanding of plant-fungus interactions and providing a potential strategy for engineering durable fungal resistance crops.