Cysteine protease that cleaves specifically after arginine or lysine residues. Does not cleave caspase-specific substrates. Required for proteolytic processing of GRI (PubMed:25398910). Inhibited by serpin ZX and nitric oxide through cysteine nitrosylation. Expressed in root tips, cauline leaves, flowers and siliques. The two subunits are derived from the precursor sequence by an autocatalytic mechanism. S-nitrosylation at Cys-147 suppresses both autoprocessing and proteolytic activity of the full-length protein, but does not affect the activity of the mature processed form. Belongs to the peptidase C14B family. Truncated N-terminus.