The secreted peptide IRP functions as a DAMP in rice immunity

Small signaling peptides play important roles in various plant processes, but information regarding their involvement in plant immunity is limited. We previously identified a novel small secreted protein in rice, named immune response peptide (IRP) by the integrated multi-omics analyses. Here, we studied IRP functions in rice immunity. Rice plants overexpressing IRP enhanced resistance to the blast fungus. Application of the IRP peptide to rice suspension cells triggered the expression of IRP itself and defense gene PAL1. RNA-seq results revealed that 84% of genes upregulated by IRP peptide were also induced by chitin, including 13 OsWRKY transcription factors, indicating that IRP and chitin share the similar signaling pathway. Co-treatment with chitin and IRP elevated the expression level of PAL1 and OsWRKYs in an additive manner. When results of IRP and PAL1 expression and MAPK activation by IRP were compared with those by chitin, IRP had a stronger effect on MAPK activation rather than IRP and PAL1 expression. Collectively, our findings indicate that IRP functions as a damage-associated molecular pattern (DAMP) in rice immunity, regulating MAPKs and OsWRKYs to amplify chitin signaling, and provide new insights into how PAMPs and DAMPs cooperatively regulate rice immunity.