Photosystem II Assembly in CP47 Mutant of Synechocystis sp. PCC 6803 Is Dependent on the Level of Chlorophyll Precursors Regulated by Ferrochelatase

Abstract

Accumulation of chlorophyll and expression of the chlorophyll (Chl)-binding CP47 protein that serves as the core antenna of photosystem II are indispensable for the assembly of a functional photosystem II. We have characterized the CP47 mutant with an impaired photosystem II assembly and its two spontaneous pseudorevertants with their much improved photoautotrophic growth. The complementing mutations in these pseudorevertants were previously mapped to the ferrochelatase gene (1). We demonstrated that complementing mutations dramatically decrease ferrochelatase activity in pseudorevertants and that this decrease is responsible for their improved photoautotrophic growth. Photoautotrophic growth of the CP47 mutant was also restored by in vivo inhibition of ferrochelatase by a specific inhibitor. The decrease in ferrochelatase activity in pseudorevertants was followed by increased steady-state levels of Chl precursors and Chl, leading to CP47 accumulation and photosystem II assembly. Similarly, supplementation of the CP47 mutant with the Chl precursor Mg-protoporphyrin IX increased the number of active photosystem-II centers, suggesting that synthesis of the mutated CP47 protein is enhanced by an increased Chl availability in the cell. The probable role of ferrochelatase in the regulation of Chl biosynthesis is discussed.

Conserved Chloroplast Open-reading Frame ycf54 Is Required for Activity of the Magnesium Protoporphyrin Monomethylester Oxidative Cyclase in Synechocystis PCC 6803

“…with 5-10% of WT levels of ferrochelatase are not deficient in heme and have no discernable phenotype (27,24), whereas Synechocystis strains with reduced levels of Chl synthase have no growth or pigmentation defects. 6 This seems be also the case of MgP methyltransferase, where strongly reduced levels still produce plenty of MgPME in the ycf54 mutant (Figs.…”

Localization of the Small CAB-like Proteins in Photosystem II

“…In this study, we did not include ScpA, suggested to have an important function in regulating the tetrapyrrole pathway at the branch point between chlorophyll biosynthesis versus heme/phycobilin biosynthesis. It has been shown that decreased ferrochelatase activity improves photoautotrophic growth of a PSII mutant because of increased supply of chlorophyll (61) and that the ScpA domain is important for the ferrochelatase function. 3 Based on the considerations provided here, the most plausible explanation regarding the function of ScpC and ScpD in light-stressed PSII is pigment storage during protein turnover.…”

Discovery of a Chlorophyll Binding Protein Complex Involved in the Early Steps of Photosystem II Assembly in Synechocystis

“…Our previous studies of PSII assembly in Synechocystis have revealed that strains unable to synthesize the inner antenna CP47 accumulate two RC assembly intermediate complexes designated RCII* and RCIIa (Sobotka et al, 2005;Dobáková et al, 2007;Komenda et al, 2008). These complexes differ in size on native gels, most probably due to the presence of additional component(s) in the larger RCII* complex.…”