Comparative genomic analysis revealed a gene for monoglucosyldiacylglycerol synthase, an enzyme for photosynthetic membrane lipid synthesis in cyanobacteria.

Graduate School for Bioscience and Biotechnology , Tokyo Institute of Technology, Yokohama 226-8501, Japan.
Plant physiology (Impact Factor: 7.39). 08/2006; 141(3):1120-7. DOI: 10.1104/pp.106.082859
Source: PubMed

ABSTRACT Cyanobacteria have a thylakoid lipid composition very similar to that of plant chloroplasts, yet cyanobacteria are proposed to synthesize monogalactosyldiacylglycerol (MGDG), a major membrane polar lipid in photosynthetic membranes, by a different pathway. In addition, plant MGDG synthase has been cloned, but no ortholog has been reported in cyanobacterial genomes. We report here identification of the gene for monoglucosyldiacylglycerol (MGlcDG) synthase, which catalyzes the first step of galactolipid synthesis in cyanobacteria. Using comparative genomic analysis, candidates for the gene were selected based on the criteria that the enzyme activity is conserved between two species of cyanobacteria (unicellular [Synechocystis sp. PCC 6803] and filamentous [Anabaena sp. PCC 7120]), and we assumed three characteristics of the enzyme; namely, it harbors a glycosyltransferase motif, falls into a category of genes with unknown function, and shares significant similarity in amino acid sequence between these two cyanobacteria. By a motif search of all genes of Synechocystis, BLAST searches, and similarity searches between these two cyanobacteria, we identified four candidates for the enzyme that have all the characteristics we predicted. When expressed in Escherichia coli, one of the Synechocystis candidate proteins showed MGlcDG synthase activity in a UDP-glucose-dependent manner. The ortholog in Anabaena also showed the same activity. The enzyme was predicted to require a divalent cation for its activity, and this was confirmed by biochemical analysis. The MGlcDG synthase and the plant MGDG synthase shared low similarity, supporting the presumption that cyanobacteria and plants utilize different pathways to synthesize MGDG.

  • [Show abstract] [Hide abstract]
    ABSTRACT: UDP-glucose pyrophosphorylase synthesizes UDP-glucose from UTP and glucose 1-phosphate, and exists in almost all species. Most bacteria possess a GalU-type UDP-glucose pyrophosphorylase, whereas many cyanobacteria species do not. In certain cyanobacteria, UDP-glucose is used as a substrate for synthesis of exopolysaccharides cellulose in spite of the absence of GalU-type UDP-glucose pyrophosphorylase. Therefore, there should be an uncharacterized UDP-glucose pyrophosphorylase in cyanobacteria. Here we show that all cyanobacteria possess a non-GalU-type bacterial UDP-glucose pyrophosphorylase, i.e., CugP, a novel family in the nucleotide triphosphate transferase superfamily. The expressed recombinant Synechocystis sp. PCC 6803 CugP had pyrophosphorylase activity that was highly specific for UTP and glucose 1-phosphate. The fact that the CugP gene cannot be deleted completely in Synechocystis sp. PCC 6803 suggests its central role as the substrate supplier for galactolipids synthesis. Galactolipids are major constituents of the photosynthetic thylakoid membrane and important for the photosynthetic activity. Based on the phylogenetic analysis, this CugP-type UDP-glucose pyrophosphorylase may have recently been horizontally transferred to certain non-cyanobacteria.
    Journal of bacteriology 04/2014; · 2.69 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The influence of arbuscular mycorrhizal (AM) fungi colonisation on photosynthesis, mineral nutrition, the amount of phospholipids and glycolipids in the leaves of olive (Olea europaea L.) trees was investigated. After six month of growth, the rate of photosynthesis, carboxylation efficiency, transpiration and stomatal conductance in mycorrhizal (M) plants was significantly higher than that of non-mycorrhizal (NM) plants. The inoculation treatment increased the foliar P and Mg but not N. The amount of glycolipids in the leaves of M plants was significantly higher than that of NM plants. However, the amount of phospholipids in the leaves of M plants was not significantly different to that in the leaves of NM plants. Also, we observed a significant increase in le level of α-linolenic acid (C18:3ω3) in glycolipids of M plants. This work support the view that increased glycolipids level in the leaves of M plants could be involved, at least in part, in the beneficial effects of mycorrhizal colonization on photosynthesis performance of olive trees. To our knowledge, this is the first report on the effect of AM fungi on the amount of glycolipids in the leaves of mycorrhizal plants.
    Journal of Plant Physiology 09/2014; · 2.77 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The thylakoid membranes of oxygenic photosynthetic organisms are dominated by the galactolipids monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG). In cyanobacteria, MGDG is synthesized via monoglucosyldiacylglycerol (GlcDG). However, the putative epimerase involved in the conversion of GlcDG to MGDG has not been identified. Here we report the identification of the gene for the glucolipid epimerase (mgdE) by comparative genomic analysis. Knockout mutants of mgdE in Synechocystis sp. PCC 6803 lacked both MGDG and DGDG and accumulated GlcDG. The mutants did possess thylakoid membranes and showed normal maximal photosynthetic activity, albeit with reduced utilization of light energy. These results cast doubt on the long-standing belief that oxygenic photosynthesis is absolutely dependent on galactolipids.
    Proceedings of the National Academy of Sciences 09/2014; · 9.81 Impact Factor


Available from