Controls stomatal patterning. Regulates asymmetric cell division during guard cell differentiation. Mediates stomatal development inhibition. Not cleaved by the protease CRSP (AC Q9LNU1) (PubMed:25043023). MEPF1: mobile signal controlling stomatal development in a non-cell-autonomous manner (PubMed:22241782). Uses ERL1 as major receptor (PubMed:22241782). May act by competing with somatogen (AC Q9SV72) for the same receptor, TMM (AC Q9SSD1) (PubMed:22027592). Interacts with ERECTA and ERL1, but not with TMM. Expressed in shoots, but not in roots. Mostly localized in developing leaves, specifically in meristemoids, guard mother cells (GMCs), and young guard cells. Not induced by high CO(2). Increased stomatal density and violation of the one-cell-spacing rule (clustering of stomata). Belongs to the plant cysteine rich small secretory peptide family. Epidermal patterning factor subfamily.