Controls stomatal patterning. Regulates the number of cells that enter, and remain in, the stomatal lineage by inhibiting protodermal cells from adopting the meristemoid mother cell (MMC) fate in a non-cell-autonomous manner. Mediates stomatal development inhibition. MEPF2: mobile signal controlling stomatal development in a non-cell-autonomous manner (PubMed:22241782). Uses ERECTA as major receptor (PubMed:22241782). Inactivated by cleavage by CRSP (AC Q9LNU1) (PubMed:25043023). May act by competing with somatogen (AC Q9SV72) for the same receptor, TMM (AC Q9SSD1) (PubMed:22027592). Interacts with ERECTA, ERL1 and TMM. Expressed in leaves, especially by the MMCs and their early descendants cells (stomatal lineage cells) including guard mother cells (GMCs). Induced by high CO(2). The loop (92-105) connecting the two anti-parallel beta-strands (85-91 and 106-112) confers the function to the peptide. Increased small pavement cell (non-stomatal) and stomatal cell density. Inversion in CO(2) control of stomatal development resulting in an increased number of stomata at elevated CO(2) concentration. Belongs to the plant cysteine rich small secretory peptide family. Epidermal patterning factor subfamily.