Cysteine protease involved in xylem tracheary element (TE) autolysis during xylogenesis in roots. Participates in micro autolysis within the intact central vacuole before mega autolysis is initiated by tonoplast implosion. Predominantly vacuolar. May be associated to plasma membrane. A number of isoforms are produced. According to EST sequences. Mostly expressed in roots, stems and flowers. Confined to tracheary elements, and specifically to xylem. Autocleaves. Belongs to the peptidase C1 family.