Cysteine protease that plays a role in immunity, senescence, and biotic and abiotic stresses (Probable). Involved in immunity against the necrotrophic fungal pathogen Botrytis cinerea (PubMed:22238602). Involved in elicitor-stimulated programmed cell death (PCD). During infection by the necrotrophic fungal pathogen Botrytis cinerea, functions as PCD-promoting protease that is released from the ER body or vacuole to the cytoplasm (PubMed:23398119). Accumulates in endoplasmic reticulum-derived bodies in epidermal cells and may participate in cell death in stressed or injured cells (PubMed:11577182). Involved in water stress-induced cell death through its protease activity that is released to the cytoplasm after vacuolar collapse (PubMed:26884487). Possesses protease activity in vitro and is involved in cell death in the transmitting tract and septum epidermis during flower development (PubMed:26160583). Possesses peptide ligase activity. Can ligate peptides to unmodified N-termini of acceptor proteins. Probably ligates through a thioester intermediate (PubMed:18660805). Inhibited by the cysteine protease inhibitor E-64. Interacts with SERPIN1 (PubMed:23398119, PubMed:20181955). Interacts with PRN2 (PubMed:24947605). Interacts with WSCP (PubMed:26160583, PubMed:26016527). Interacts with TZF4, TZF5 and TZF6 (PubMed:26978070). Specifically accumulates in body structures that directly bud from the endoplasmic reticulum and fuse with the vacuole (PubMed:11577182). Passes through the Golgi on its route to the vacuole (PubMed:22396764). By high salt conditions and drought stress. No visible phenotype under normal growth conditions (PubMed:22238602, PubMed:22396764). Mutant plants show increased susceptibility to infection by the necrotrophic fungal pathogen Botrytis cinerea (PubMed:22238602). Belongs to the peptidase C1 family.