Identification and Characterization of OsSSIP, a Conserved Immune Peptide Regulating Rice Defense

Rice blast, caused by Magnaporthe oryzae, poses a serious threat to crop yield; however, immune-active small secreted peptides associated with this disease remain largely uncharacterized. In this study, we identified OsSSIP, a pathogen-inducible peptide in rice. OsSSIP-related similar sequences are widely distributed across angiosperms, while canonical signal peptides appear to be predominantly enriched in Poaceae. Strikingly, the SSP-like homologs of OsSSIP share a conserved N-terminal Tyr-Cys core motif that is essential for OsSSIP activity. Exogenous application of OsSSIP triggered early reactive oxygen species burst, mitogen-activated protein kinase phosphorylation, and defense-related gene expression, while also inhibiting rice root growth. Overexpression of ProOsSSIP enhanced disease resistance accompanied by transient growth suppression, whereas knockout mutants exhibited compromised immunity. A scalable recombinant five-copy OsSSIP protein produced in Escherichia coli effectively mimicked the native peptide. Both OsSSIP and the recombinant protein elicited immune responses not only in rice and wheat but also in dicots such as tomato, soybean, and Arabidopsis. Furthermore, two chemically synthesized peptides derived from non-signal-peptide similar sequences also displayed immune activity. Collectively, this work demonstrates a previously unappreciated role of OsSSIP in rice immunity against blast disease and highlights the potential of exogenous OsSSIP as an eco-friendly immune stimulator for broad-spectrum crop disease control.