Thiol protease that possesses high activity toward the cathepsin synthetic substrate Arg-Arg-7-amino-4-methylcoumarin (RR-AMC) and the papain substrate Gly-Arg-Arg-AMC (GRR-AMC). Can cleave the papain substrate Phe-Arg-AMC (FR-AMC) and the caspase-3 substrate Asp-Glu-Val-Asp-rhodamine 110 (DEVD-R110). Has no activity towards the caspase-6 substrate VEID-AMC, caspase-8 substrate IETD-AMC and caspase-1 substrate YVAD-AMC (PubMed:27058316). Plays a central role in plant programmed cell death (PCD). In addition to its role in protein degradation, may cleave and/or degrade a number of target proteins, activating signaling towards PCD. Contributes to the increase of caspase-3-like activity after UV-C-induced PCD and is required for abiotic stress-induced PCD (PubMed:27058316). Functions redundantly with CATHB1 and CATHB2 in basal defense and distinct forms of plant programmed cell death (PCD). Participates in the establishment of basal resistance against the bacterial pathogen Pseudomonase syringae pv. tomato DC3000. Required for full levels of PCD during resistance (R) gene-mediated hypersensitive response (HR). Involved in the regulation of senescence, a developmental form of PCD in plants (PubMed:19453434). May be involved in the degradation of seed storage proteins during seed germination (PubMed:24600022). Inhibited by the cathepsin B inhibitors Ac-LVK-CHO, CA-074 and Z-FA-FMK, and the caspase-3 inhibitor Z-DEVD-CHO. Optimum pH is 5.5. Expressed in root tips, root vasculature, emerging lateral root, hydathodes, vascular tissue of leaves, vasculature of sepals and anthers, stigma, and vascular bundles at the base and the upper part of the siliques. Expressed in developing siliques 13 to 15 days after pollination (DAP). In germinating seeds, expressed from 12 to 48 hours after imbibition with a peak of expression at 24 hours. By dark-induced senescence. Induced by infection with an avirulent strain of the bacterial pathogen Pseudomonase syringae pv. tomato DC3000. Delayed germination and decreased germination rate. Belongs to the peptidase C1 family.