A chloroplastic inner envelope membrane protease is essential for plant development.

Regulated intramembrane proteolysis (RIP) is a fundamental mechanism for controlling a wide range of cellular functions. Cleavage of membrane embedded proteins results in soluble fragments exerting their function, e.g., as transcription factors and thereby regulating gene expression. This process is highly conserved throughout all kingdom of life as are the involved proteases. RIP has been described in eukaryotes, bacteria and archea though until recently not in plant organelles. Here we describe a chloroplastic membrane protease which belongs to the conserved S2P family of membrane metallo proteases. We show that this protease is localized in the inner envelope membrane and is essential for plant development. It could function in a RIP like process regulating the concordant action in the plant cytosol, nucleus and plastids.