Mediates CO(2)-controlled stomatal development by cleaving peptide EPF2 (AC Q8LC53). Not active on peptides EPF1 (AC Q8S8I4) or stomagen (AC Q9SV72). Release of an N-terminal tripeptide from a polypeptide. Expressed in roots, guard cells and meristemoid and pavement cells. Induced by high CO(2). Increased stomata number at elevated CO(2) concentration and increased number of epidermal cells. Belongs to the peptidase S8 family.