Essential protease involved in epiderm development. Required for aleurone cell development in the endosperm probably by maintaining and restricting the aleurone and embryonic epidermal L1 cell-layer fates as well as meristems organization. Involved in the maintenance of adaxial/abaxial axis information in developing leaves, probably by regulating cell proliferation and expansion. Does not need calcium ions to be active. Ubiquitously expressed with higher levels in embryos, vasculatures, leaf primordia, leaf margins, and shoot apical meristem (SAM). The transmembrane regions are not required for calpain activity but may play regulatory roles. Autocatalytic proteolytic cleavage leading to the production of mainly cytoplasmic localized subproducts of about 85 and 120 kDa. Abnormal embryos arrested at the globular stage with an abnormal aleurone layer on the ventral side. Although homology to other calpains is high within the protease domain, the lack of calcium-binding sites suggests that this protein is a protease that may not be activated by calcium ions. Belongs to the peptidase C2 family.