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Microbe-associated molecular pattern ( MAMP)-triggered immunity plays critical roles in the basal resistance defense response in plants. Chitin and peptidoglycan ( PGN) are major molecular patterns for fungi and bacteria, respectively. Two rice ( Oryza sativa) lysin motif-containing proteins, Os LYP4 and Os LYP6, function as receptors that sense bacterial PGN and fungal chitin. These membrane receptors, which lack intracellular kinase domains, likely contain another component for transmembrane immune signal transduction. Here, we demonstrate that the rice LysM receptor-like kinase Os CERK1, a key component of the chitin elicitor signaling pathway, also plays an important role in PGN-triggered immunity in rice. Silencing of Os CERK1 suppressed PGN-induced (and chitin-induced) immunity responses, including reactive oxygen species generation, defense gene expression, and callose deposition, indicating that Os CERK1 is essential for both PGN and chitin signaling initiated by Os LYP4 and Os LYP6. Os LYP4 associated with Os LYP6 and the rice chitin receptor chitin oligosaccharide elicitor-binding protein ( CEBiP) in the absence of PGN or chitin, and treatment with PGN or chitin led to their disassociation in vivo. Os CERK1 associated with Os LYP4 or Os LYP6 when induced by PGN but it associated with Os LYP4, Os LYP6, or CEBiP under chitin treatment, suggesting the presence of different patterns of ligand-induced heterooligomeric receptor complexes. Furthermore, the receptor-like cytoplasmic kinase Os RLCK176 functions downstream of Os CERK1 in the PGN and chitin signaling pathways, suggesting that these MAMPs share overlapping intracellular signaling components. Therefore, Os CERK1 plays dual roles in PGN and chitin signaling in rice innate immunity and as an adaptor involved in signal transduction at the plasma membrane in conjunction with Os LYP4 and Os LYP6. [ABSTRACT FROM AUTHOR]