Chloroplasts have a dynamic protein environment and, although proteases are presumably major contributors, the identities of these crucial regulatory proteins have only recently been revealed. There are defined proteases within each of the major chloroplast compartments: the ATP-dependent Clp and FtsH proteases in the stroma and stroma-exposed thylakoid membranes, respectively, the ATP-independent DegP proteases within the thylakoid lumen and on both sides of thylakoid membranes, and the SppA protease on the stromal side of the thylakoid. All four types are homologous to proteases characterized in bacteria, but most have many isomers in higher plants. With such diversity, the challenge is to link the mode of action of each protease to the chloroplast enzymes and regulatory proteins that it targets.
Bibliographical noteFunding Information:
We thank Gil Adam for the artwork. The work in Z.A.'s laboratory was supported by grants from the USA–Israel Binational Agricultural Research and Development (BARD) Fund, the USA–Israel Binational Science Foundation (BSF) and the Israel Science Foundation (ISF). Work in A.K.C.'s laboratory was supported by grants from the Swedish Research Council (VR), the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (Formas) and the Swedish Foundation for International Co-operation in Research and Education (STINT).