Cleavage of a pathogen apoplastic protein by plant subtilases activates host immunity

The plant apoplast is a harsh environment in which hydrolytic enzymes, especially proteases, accumulate during pathogen infection. However, the defense functions of most apoplastic proteases remain largely elusive. We show here that newly identified small cysteine-rich secreted protein PC2 from potato late blight Phytophthora infestans induces immunity Solanum plants only after cleavage by subtilisin-like such as tomato P69B. A minimal 61 amino acid core peptide carrying two key cysteines, conserved widely oomycete species, sufficient for PC2-induced cell death. Furthermore, we showed Kazal-like protease inhibitors, EPI1, produced P. prevent and dampen elicited host immunity. This study reveals proteins to release immunogenic peptides an important function proteases.