Fungal resistance in rice is restored by interfamily transfer of an evolutionarily lost co-receptor

The interfamily transfer of pattern-recognition receptors (PRRs) offers a promising strategy to enhance plant immunity; however, factors causing functional limitations across species remain unknown. Here, we identify secreted TOM20 domain-containing protein (STOM), a previously uncharacterized fungal microbe-associated molecular pattern (MAMP) that triggers immunity in Nicotiana benthamiana but not in rice (Oryza sativa). We identify NbSTOMR as the receptor that recognizes and binds STOM, and NbSTOMRh as the co-receptor that, despite lacking ligand-binding ability, is essential through its extracellular interaction with NbSTOMR. Transferring NbSTOMR to rice fails to confer resistance, but NbSTOMRh alone enhances resistance to false smut and blast disease. Evolutionary analyses reveal that while STOMR is conserved, monocots have lost STOMRh due to transposon-mediated chromosomal separation of its extracellular domain. Although OsSTOMR binds STOM, OsSTOMRh is non-functional; however, NbSTOMRh promotes OsSTOMR-dependent STOM recognition. These findings highlight the critical role of co-receptors in overcoming taxonomic barriers and provide a strategy for reconstituting PRR-mediated immunity in monocot crops.