Small signaling peptides, generated from larger protein precursors, are important components to orchestrate various plant processes such as development and immune responses.

However, small signaling peptides involved in plant immunity remain largely unknown. Here, we developed a pipeline using transcriptomicsand proteomics-based screening to identify putative precursors of small signaling peptides:small secreted proteins (SSPs) in rice, induced by rice blast fungus Magnaportheoryzaeand its elicitor, chitin. We identified 236 SSPs including members of two known small signalingpeptide familiesnamely rapid alkalinization factors and phytosulfokines, as well as many other protein families that are known to be involved in immunity, such as proteinase inhibitors and pathogenesis-related protein families. We also isolated 52 unannotated SSPs, and among them, we found one gene which we namedimmune response peptide(IRP)that appeared to encode the precursor of a small signalingpeptide regulating rice immunity. In rice suspension cells, the expression of IRPwas induced by bacterial peptidoglycan andfungal chitin.Overexpression of IRP enhanced the expression of adefence gene, PAL1and induced the activation of the MAPKs inrice cells. Moreover, the IRP protein level increased insuspension cell medium after chitin treatment. Collectively, we established a simple and efficient pipelineto discover SSPcandidates that may play important roles in rice immunity, and identified 52 unannotated SSPs that may be useful for further elucidation of rice immunity. Our method may be applied to identify SSPs that are involved not only in immunity but also in other plant functions. This article is protected by copyright. All rights reserved.