Comparative and evolutionary aspects of cyanobacteria and plant plastid division study

The review summarizes the current understanding of cyanobacterial cell division mechanisms in comparison with those of eukaryotic plastids. It also sheds light on the present knowledge of the nature of evolutionary transformations of the cyanobacterial cell division apparatus that could have occurred during the establishment of modern plastid division complex. Peculiar properties of cyanobacterial cell division process are discussed as well as the features of primary and secondary plastid replication.     

A novel gene that bears a DnaJ motif influences cyanobacterial cell division

Transposon Tn5-692 mutagenizes Synechococcus sp. strain PCC 7942 efficiently. The predicted product of the gene mutated in the Tn5-692-derived cell division mutant FTN2 has an N-terminal DnaJ domain, as have its cyanobacterial and plant orthologs. Anabaena sp. strain PCC 7120, when mutated in genes orthologous to ftn2 and ftn6, forms akinete-like cells.     

Novel DNA-binding proteins in the cyanobacterium Anabaena sp. strain PCC 7120

As an approach towards elucidation of the biochemical regulation of the progression of heterocyst differentiation in Anabaena sp. strain PCC 7120, we have identified proteins that bind to a 150-bp sequence upstream from hepC, a gene that plays a role in the synthesis of heterocyst envelope polysaccharide. Such proteins were purified in four steps from extracts of vegetative cells of Anabaena sp. Two of these proteins (Abp1 and Abp2) are encoded by neighboring genes in the Anabaena sp. chromosome. The genes that encode the third (Abp3) and fourth (Abp4) proteins are situated at two other loci in that chromosome. Insertional mutagenesis of abp2 and abp3 blocked expression of hepC and hepA and prevented heterocyst maturation and aerobic fixation of N(2).     

Genetic and biochemical evidence for distinct key functions of two highly divergent GAPDH genes in catabolic and anabolic carbon flow of the cyanobacterium Synechocystis sp. PCC 6803

Cyanobacterial genomes harbour two separate highly divergent glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes, gap1 and gap2, which are closely related at the sequence level to the nuclear genes encoding cytosolic and chloroplast GAPDH of higher plants, respectively. Genes gap1 and gap2 of the unicellular cyanobacterium Synechocystis sp. PCC 6803 were cloned and sequenced and subsequently inactivated by insertional mutagenesis to understand their metabolic functions. We obtained homozygous gap1^- mutants which have lost the capacity to grow on glucose under dim light while growth on organic acids as well as photosynthetic growth under CO₂ and high light is not impaired. Homozygous gap2^- mutants show the reciprocal phenotype. Under dim light they only grow on glucose but not on organic acids nor do they survive under photosynthetic conditions. Measurements of the anabolic activities (reduction of 1,3-bisphosphoglycerate) in extracts from wild type and mutant cells show that Gap2 is a major enzyme with dual cosubstrate specificity for NAD and NADP, while Gap1 displays a minor NAD-specific GAPDH activity. However, if measured in the catabolic direction (oxidation of glyceraldehyde-3-phosphate) Gap2 activity is very low and increases three- to fivefold after gel filtration of extracts over Sephadex G25. Our results suggest that enzymes Gap1 and Gap2, although coexpressed in cyanobacterial wild-type cells, play distinct key roles in catabolic and anabolic carbon flow, respectively. While Gap2 operates in the photosynthetic Calvin cycle and in non-photosynthetic gluconeogenesis, Gap1 seems to be essential only for glycolytic glucose breakdown, conditions under which the catabolic activity of Gap2 seems to be repressed by a specific low-molecular-weight inhibitor.     

Effect of red light on activity of cAMP phosphodiesterases in photoperiodically different cereals and vernalized winter wheat

Red light illumination of seedlings of photoperiodically different cereals had a different effect on the activity of multiple cyclic adenosine monophosphate phosphodiesterases. The response of all phosphodiesterase forms was reversed in fully vernalized winter wheat Triticum aestivum L.     

Mutants of Burkholderia cenocepacia with a change in synthesis of N-acyl-homoserine lactones--signal molecules of Quorum Sensing regulation

By means of plasposon mutagenesis, mutants of Burkholderia cenocepacia 370 with the change in production of N-acyl-homoserine lactones (AHL), signal molecules of the Quorum Sensing system of regulation, were obtained. To localize plasposon insertions in mutant strains, fragments of chromosomal DNA containing plasposons were cloned, adjacent DNA regions sequenced, and a search for homologous nucleotide sequences in the GeneBank was initiated. It has been shown that the insertion of plasposon into gene lon encoding lon proteinase drastically decreases AHL synthesis. Upon insertion of plasposon into gene pps encoding phosphoenolpyruvate-synthase, enhancement of AHL production is observed. In mutant carrying inactivated gene lon, a strong decline of extracellular protease activity, hemolytic, and chitinolytic activities was observed in comparison with the original strain; lipase activity was not changed in this mutant. Mutation in gene pps did not affect these properties of B. cenocepacia 370. Mutations in genes lon and pps reduced the virulence of bacteria upon infection of mice.     

Neurotoxic non-proteinogenic amino acid β-<Emphasis Type="Italic">N</Emphasis>-methylamino-L-alanine and its role in biological systems

Secondary metabolites of photoautotrophic organisms have attracted considerable interest in recent years. In particular, molecules of non-proteinogenic amino acids participating in various physiological processes and capable of producing adverse ecological effects have been actively investigated. For example, the non-proteinogenic amino acid β-Nmethylamino-L-alanine (BMAA) is neurotoxic to animals including humans. It is known that BMAA accumulation via the food chain can lead to development of neurodegenerative diseases in humans such as Alzheimer’s and Parkinson’s diseases as well as amyotrophic lateral sclerosis. Moreover, BMAA can be mistakenly incorporated into a protein molecule instead of serine. Natural sources of BMAA and methods for its detection are discussed in this review, as well as the role of BMAA in metabolism of its producers and possible mechanisms of toxicity of this amino acid in different living organisms.     

The gap1 operon of the cyanobacterium Synechococcus PCC 7942 carries a gene encoding glycogen phosphorylase and is induced under anaerobic conditions

The cloning and sequencing of the gap1 operon, which encodes the glycolytic NAD-specific glyceraldehyde-3-phosphate dehydrogenase in the cyanobacterium Synechococcus PCC 7942, showed that the gap1 gene is closely linked to the glgP gene encoding glycogen phosphorylase (an enzyme that catalyzes the first step of glycogen degradation). Northern blotting experiments showed that the gap1 and glgP genes are co-expressed and organized in a bicistronic operon, whose expression is enhanced under anaerobic conditions. The nucleotide sequence of the operon has been submitted to GenBank under accession number AF428099.     

The pleiotropic effects of ftn2 and ftn6 mutations in cyanobacterium Synechococcus sp. PCC 7942

Two cell division mutants (Ftn2 and Ftn6) of the cyanobacterium Synechococcus sp. PCC 7942 were studied using scanning electron microscopy and transmission electron microscopy methods. This included negative staining and ultrathin section analysis. Different morphological and ultrastructural features of mutant cells were identified. Ftn2 and Ftn6 mutants exhibited particularly elongated cells characterized by significantly changed shape in comparison with the wild type. There was irregular bending, curving, spiralization, and bulges as well as cell branching. Elongated mutant cells were able to initiate cytokinesis simultaneously in several division sites which were localized irregularly along the cell. Damaged rigidity of the cell wall was typical of many cells for both mutants. Thylakoids of mutants showed modified arrangement and ultrastructural organization. Carboxysome-like structures without a shell and/or without accurate polyhedral packing protein particles were often detected in the mutants. However, in the case of Ftn2 and Ftn6, the average number of carboxysomes per section was less than in the wild type by a factor of 4 and 2, respectively. These multiple morphological and ultrastructural changes in mutant cells evinced pleiotropic responses which were induced by mutations in cell division genes ftn2 and ftn6. Ultrastructural abnormalities of Ftn2 and Ftn6 mutants were consistent with differences in their proteomes. These results could support the significance of FTN2 and FTN6 proteins for both cyanobacterial cell division and cellular physiology.