Metallopeptidase that binds to the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA). Required for embryonic and seedling development as well as cell cycle progression. Homodimerization is required to proper localization and activity. May play a negative role in the regulation of PIN auxin transport proteins. Release of an N-terminal amino acid, Xaa-|-Yaa- from a peptide, amide or arylamide. Xaa is preferably Ala, but may be most amino acids including Pro (slow action). When a terminal hydrophobic residue is followed by a prolyl residue, the two may be released as an intact Xaa-Pro dipeptide. Binds 1 zinc ion per subunit. Homodimer. Interacts with N-1-naphthylphthalamic acid (NPA). The dileucine internalization motif may be involved in intracellular sequestration. Ubiquitous with preferential expression in 5 days-old seedlings, roots, young flowers, upper inflorescence stems, and rosette leaves. Expression starts at 3 days and peaks at 5 days. After, expression levels remain constant from 7 to 10 days. During embryogenesis, expressed first at the site of root meristem formation, then in the epidernal and ground tissue, root meristem and suspensor. In the mature embryo, expressed in the vascular primordia throughout the hypocotyl/root axis. Dileucine motif seems to be involved in protein-protein interactions. Loss-of-function mutants show irregular, uncoordinated cell divisions throughout embryogenesis, affecting the shape and number of cotyledons and the hypophysis, and is seedling lethal at 5 days after germination due to root growth arrest. Quiescent center and cell cycle markers show no signals in apm1-1 knockdown mutants, and the ground tissue specifiers SHORTROOT and SCARECROW are misexpressed or mislocalized. apm1 mutants have multiple, fused cotyledons and hypocotyls with enlarged epidermal cells with cell adhesion defects. apm1 alleles show defects in gravitropism and auxin transport. Belongs to the peptidase M1 family. Truncated N-terminus.