Assembly of Photosystem II in chloroplast psbEFLJ operon mutants

Abstract

Assembly and/or stabilization of the PSII complex has been studied in tobacco psbEFLJ operon mutants, each type lacking one of the genes. The core of PSII consists of the D1 and D2 proteins, the cytochrome b559, the chlorophyll a binding complexes CP43 and CP47 and a number of smaller proteins including the psbL and psbJ gene products. Cytochrome b559 is a thylakoid membrane-embedded heme protein and is composed of two subunits, a and b , encoded by the chloroplast psbE and psbF genes. Two-dimensional blue-native gel electrophoresis was used to study the assembly of thylakoid protein complexes in psbEFLJ operon mutants. All proteins encoded by the operon, PsbE, PsbF, PsbL and PsbJ are necessary for normal assembly of PSII core monomer. No PSII assemblies were observed in ?psbE mutants whereas the ?psbF mutants allowed transient D1/D2 heterodimer to be detected in thylakoid membranes. PsbL appeared to be particularly needed for stable assembly of CP43 into PSII core. When PsbJ protein was missing, the amount and stability of PSII complexes are strongly reduced. PSI, LHCII and cytochome b6f complexes were normally assembled in all mutants. Thylakoid membrane organization was severly altered in ?psbE and ?psbF mutants with significantly lower amount of grana stacks composed of only a few appressed thylakoids.