Membrane-associated and ATP-independent metalloprotease required for development of both thylakoid grana and well-organized lamellae in chloroplast. Required for the accumulation of chlorophyll and chlorophyll a/b binding (CAB) proteins (from both PS I and PS II) in chloroplast membranes, and for grana formation and normal chloroplast development. Involved in the regulation of nuclear gene expression in response to ammonium stress and interacts with ABA signaling. Carries out beta-casein degradation in an ATP-independent manner in vitro. Localizes in endodermal and cortex plastids. Expressed in roots, leaves, cotyledons, hypocotyls, stems, flowers and siliques. By ethylene. Down-regulated by dark. Reduced chlorophyll accumulation, defects in chloroplast development and abnormal hypocotyl gravicurvature. Belongs to the peptidase M50B family.