Lack of the small plastid-encoded PsbJ polypeptide results in inefficient photosystem II function, reduced photosystem I levels and hypersensitivity to light

Abstract

Photosystem II is a large pigment-protein complex catalyzing water oxidation, initiating electron transfer processes and translocating protons across the thylakoid membrane. In addition to large cofactor-binding protein subunits, photosystem II particles also contain a number of low molecular weight polypeptides whose function is only poorly defined. Here we have investigated the function of one of the smallest polypeptides in photosystem II, PsbJ. Using a reverse genetics approach, we have inactivated the psbJ gene in the tobacco chloroplast genome. We show that although the PsbJ polypeptide is not principally required for functional photochemistry in thylakoid membranes, plants lacking PsbJ are unable to grow photoautotrophically. We demonstrate that this is due to inefficient photosystem II function which in turn causes downregulation of photosystem I and extreme sensitivity to light. Our results (i) suggest a role of PsbJ in the assembly of stable and functional photosystem II complexes and (ii) support a control of photosystem I accumulation through photosystem II activity.