The negatively charged lipid phosphatidylglycerol (PG) constitutes up to 10% of total lipids in photosynthetic membranes, and its deprivation in cyanobacteria is accompanied by chlorophyll (Chl) depletion. Indeed, radioactive labeling of the PG-depleted ΔpgsA mutant of Synechocystis sp. strain PCC 6803, which is not able to synthesize PG, proved the inhibition of Chl biosynthesis caused by restriction on the formation of 5-aminolevulinic acid and protochlorophyllide. Although the mutant accumulated chlorophyllide, the last Chl precursor, we showed that it originated from dephytylation of existing Chl and not from the block in the Chl biosynthesis. The lack of de novo-produced Chl under PG depletion was accompanied by a significantly weakened biosynthesis of both monomeric and trimeric photosystem I (PSI) complexes, although the decrease in cellular content was manifested only for the trimeric form. However, our analysis of ΔpgsA mutant, which lacked trimeric PSI because of the absence of the PsaL subunit, suggested that the virtual stability of monomeric PSI is a result of disintegration of PSI trimers. Interestingly, the loss of trimeric PSI was accompanied by accumulation of monomeric PSI associated with the newly synthesized CP43 subunit of photosystem II. We conclude that the absence of PG results in the inhibition of Chl biosynthetic pathway, which impairs synthesis of PSI, despite the accumulation of chlorophyllide released from the degraded Chl proteins. Based on the knowledge about the role of PG in prokaryotes, we hypothesize that the synthesis of Chl and PSI complexes are colocated in a membrane microdomain requiring PG for integrity.

• MeSH
• Bacterial Proteins genetics   metabolism   MeSH
• Chlorophyll biosynthesis   metabolism   MeSH
• Chlorophyllides metabolism   MeSH
• Phosphatidylglycerols genetics   metabolism   MeSH
• Photosystem I Protein Complex metabolism   MeSH
• Carbon-Oxygen Ligases metabolism   MeSH
• Protochlorophyllide metabolism   MeSH
• Light-Harvesting Protein Complexes metabolism   MeSH
• Synechocystis genetics   metabolism   MeSH
• Transferases (Other Substituted Phosphate Groups) genetics   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

In most oxygenic phototrophs, including cyanobacteria, two independent enzymes catalyze the reduction of protochlorophyllide to chlorophyllide, which is the penultimate step in chlorophyll (Chl) biosynthesis. One is light-dependent NADPH:protochlorophyllide oxidoreductase (LPOR) and the second type is dark-operative protochlorophyllide oxidoreductase (DPOR). To clarify the roles of both enzymes, we assessed synthesis and accumulation of Chl-binding proteins in mutants of cyanobacterium Synechocystis PCC 6803 that either completely lack LPOR or possess low levels of the active enzyme due to its ectopic regulatable expression. The LPOR-less mutant grew photoautotrophically in moderate light and contained a maximum of 20 % of the wild-type (WT) Chl level. Both Photosystem II (PSII) and Photosystem I (PSI) were reduced to the same degree. Accumulation of PSII was mostly limited by the synthesis of antennae CP43 and especially CP47 as indicated by the accumulation of reaction center assembly complexes. The phenotype of the LPOR-less mutant was comparable to the strain lacking DPOR that also contained <25 % of the wild-type level of PSII and PSI when cultivated under light-activated heterotrophic growth conditions. However, in the latter case, we detected no reaction center assembly complexes, indicating that synthesis was almost completely inhibited for all Chl-proteins, including the D1 and D2 proteins.

• MeSH
• Electrophoresis, Gel, Two-Dimensional MeSH
• Enzyme Activation MeSH
• Bacterial Proteins genetics   metabolism   MeSH
• Cell Membrane enzymology   metabolism   MeSH
• Chlorophyll biosynthesis   genetics   MeSH
• Electrophoresis, Polyacrylamide Gel MeSH
• Phenotype MeSH
• Photosystem I Protein Complex genetics   metabolism   MeSH
• Photosystem II Protein Complex genetics   metabolism   MeSH
• Phototrophic Processes MeSH
• Oxidoreductases Acting on CH-CH Group Donors genetics   metabolism   MeSH
• Protochlorophyllide metabolism   MeSH
• Gene Expression Regulation, Enzymologic * MeSH
• Gene Expression Regulation, Plant MeSH
• Light MeSH
• Synechocystis enzymology   genetics   metabolism   radiation effects   MeSH
• Transformation, Genetic MeSH
• Protein Binding MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH