Publications (13)41.81 Total impact
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Article: Deletion of the transcriptional regulator cyAbrB2 de-regulates primary carbon metabolism in Synechocystis sp. PCC 6803.
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ABSTRACT: cyAbrB is a transcriptional regulator unique to and highly conserved among cyanobacterial species. A gene-disrupted mutant of cyabrB2 (sll0822) in Synechocystis sp. PCC 6803 exhibited severe growth inhibition and abnormal accumulation of glycogen granules within cells under photomixotrophic conditions. Within 6 h after the shift to photomixotrophic conditions, NaHCO3-dependent oxygen evolution activity markedly declined in the ΔcyabrB2 mutant, but the decrease in methyl viologen-dependent electron transport activity was much smaller, indicating inhibition in CO2 fixation. Decreases in the transcript levels of several genes related to sugar catabolism, CO2 fixation, and nitrogen metabolism were also observed within 6 h. Metabolome analysis by capillary electrophoresis mass spectrometry (CE/MS) revealed that several metabolites accumulated differently in the wild-type and mutant strains. For example, the amounts of pyruvate and 2-oxoglutarate (2OG) were significantly lower in the mutant than in the wild-type, irrespective of trophic conditions. The growth rate of the ΔcyabrB2 mutant was restored to a level comparable to that under photoautotrophic conditions by addition of 2OG to the growth medium under photomixotrophic conditions. Activities of various metabolic processes, including CO2 fixation, respiration, and nitrogen assimilation, seemed to be enhanced by 2OG addition. These observations suggest that cyAbrB2 is essential for the active transcription of genes related to carbon and nitrogen metabolism upon a shift to photomixotrophic conditions. Deletion of cyAbrB2 is likely to de-regulate the partition of carbon between storage forms and soluble forms used for biosynthetic purposes. This disorder may cause inactivation of cellular metabolism, excess accumulation of reducing equivalents, and subsequent loss of viability under photomixotrophic conditions.Plant physiology 04/2013; · 6.53 Impact Factor -
Article: Cold acclimation in the moss Physcomitrella patens involves abscisic acid-dependent signaling.
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ABSTRACT: Overwintering plants develop tolerance to freezing stress through a cold acclimation process by which the cells provoke internal protective mechanisms against freezing. The stress hormone abscisic acid (ABA) is known to increase freezing tolerance of plant cells, but its role in cold acclimation has not been determined. In this study, we used ABA-insensitive lines of the moss Physcomitrella patens to determine whether cold acclimation in bryophytes involves an ABA-dependent process. Two ABA-insensitive lines, both impaired in ABA signaling without showing ABA-induced stress tolerance, were subjected to cold acclimation, and changes in freezing tolerance and accumulation of soluble sugars and proteins were compared to the wild type. The wild-type cells acquired freezing tolerance in response to cold acclimation treatment, but very little increase in freezing tolerance was observed in the ABA-insensitive lines. Analysis of low-molecular-weight soluble sugars indicated that the ABA-insensitive lines accumulated sucrose, a major compatible solute in bryophytes, to levels comparable with those of the wild type during cold acclimation. However, accumulation of the trisaccharide theanderose and of specific LEA-like boiling-soluble proteins was very limited in the ABA-insensitive lines. Furthermore, analysis of cold-induced expression of genes encoding LEA-like proteins revealed that the ABA-insensitive lines accumulate only small amounts of these transcripts during cold acclimation. Our results indicate that cold acclimation of bryophytes requires an ABA-dependent signaling process. The results also suggest that cold-induced sugar accumulation, depending on the sugar species, can either be dependent or independent of the ABA-signaling pathway.Journal of plant physiology 09/2011; 169(2):137-45. · 2.50 Impact Factor -
Article: Physiological roles of the cyAbrB transcriptional regulator pair Sll0822 and Sll0359 in Synechocystis sp. strain PCC 6803.
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ABSTRACT: All known cyanobacterial genomes possess multiple copies of genes encoding AbrB-like transcriptional regulators, known as cyAbrBs, which are distinct from those conserved among other bacterial species. In this study, we addressed the physiological roles of Sll0822 and Sll0359, the two cyAbrBs in Synechocystis sp. strain PCC 6803, under nonstress conditions (20 μmol of photons m⁻² s⁻¹ in ambient CO₂). When the sll0822 gene was disrupted, the expression levels of nitrogen-related genes such as urtA, amt1, and glnB significantly decreased compared with those in the wild-type cells. Possibly due to the increase of the cellular carbon/nitrogen ratio in the sll0822-disrupted cells, a decrease in pigment contents, downregulation of carbon-uptake related genes, and aberrant accumulation of glycogen took place. Moreover, the mutant exhibited the decrease in the expression level of cytokinesis-related genes such as ftsZ and ftsQ, resulting in the defect in cell division and significant increase in cell size. The pleiotrophic phenotype of the mutant was efficiently suppressed by the introduction of Sll0822 and also partially suppressed by the introduction of Sll0359. When His-tagged cyAbrBs were purified from overexpression strains, Sll0359 and Sll0822 were copurified with each other. The cyAbrBs in Synechocystis sp. strain PCC 6803 seem to interact with each other and regulate carbon and nitrogen metabolism as well as the cell division process under nonstress conditions.Journal of bacteriology 06/2011; 193(15):3702-9. · 3.94 Impact Factor -
Article: Rice Brittle culm 6 encodes a dominant-negative form of CesA protein that perturbs cellulose synthesis in secondary cell walls.
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ABSTRACT: The brittle culm (bc) mutants of Gramineae plants having brittle skeletal structures are valuable materials for studying secondary cell walls. In contrast to other recessive bc mutants, rice Bc6 is a semi-dominant bc mutant with easily breakable plant bodies. In this study, the Bc6 gene was cloned by positional cloning. Bc6 encodes a cellulose synthase catalytic subunit, OsCesA9, and has a missense mutation in its highly conserved region. In culms of the Bc6 mutant, the proportion of cellulose was reduced by 38%, while that of hemicellulose was increased by 34%. Introduction of the semi-dominant Bc6 mutant gene into wild-type rice significantly reduced the percentage of cellulose, causing brittle phenotypes. Transmission electron microscopy analysis revealed that Bc6 mutation reduced the cell wall thickness of sclerenchymal cells in culms. In rice expressing a reporter construct, BC6 promoter activity was detected in the culms, nodes, and flowers, and was localized primarily in xylem tissues. This expression pattern was highly similar to that of BC1, which encodes a COBRA-like protein involved in cellulose synthesis in secondary cell walls in rice. These results indicate that BC6 is a secondary cell wall-specific CesA that plays an important role in proper deposition of cellulose in the secondary cell walls.Journal of Experimental Botany 01/2011; 62(6):2053-62. · 5.36 Impact Factor -
Article: Rice BRITTLE CULM 3 (BC3) encodes a classical dynamin OsDRP2B essential for proper secondary cell wall synthesis.
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ABSTRACT: "Brittle culm" mutants found in Gramineae crops are suitable materials to study the mechanism of secondary cell wall formation. Through positional cloning, we have identified a gene responsible for the brittle culm phenotype in rice, brittle culm 3 (bc3). BC3 encodes a member of the classical dynamin protein family, a family known to function widely in membrane dynamics. The bc3 mutation resulted in reductions of 28-36% in cellulose contents in culms, leaves, and roots, while other cell wall components remained unaffected. Reductions of cell wall thickness and birefringence were observed in both fiber (sclerenchyma) and parenchymal cells, together with blurring of the wall's layered structures. From promoter-GUS analyses, it was suggested that BC3 expression is directly correlated with active secondary cell wall synthesis. These results suggest that BC3 is tightly involved in the synthesis of cellulose and is essential for proper secondary cell wall construction.Planta 04/2010; 232(1):95-108. · 3.00 Impact Factor -
Article: Rice BRITTLE CULM 5 (BRITTLE NODE) is involved in secondary cell wall formation in the sclerenchyma tissue of nodes.
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ABSTRACT: Several brittle culm (bc) mutants known in grasses are considered excellent materials to study the process of secondary cell wall formation. The brittle phenotype of the rice bc5 (brittle node) mutant appears exclusively in the developed nodes, which is distinct from other bc mutants (bc1, 2, 3, 4, 6 and 7) that show the brittle phenotype in culms and leaves. To address the defects of the rice bc5 mutant in node-specific cell wall formation, we analyzed tissue morphology and cell wall composition. The bc5 mutation was found to affect the cell wall deposition of node sclerenchyma tissues at 1 week after heading, the stage at which the cell wall sugar content is reduced, in the bc5 nodes, compared with wild-type nodes. Moreover, decreased accumulation of lignin and thickness of cell walls in the sclerenchyma tissues were also observed in the bc5 nodes. The amounts of cellulose and hemicellulose were reduced to 53 and 65% of those in the wild-type plants, respectively. Sugar composition and glycosidic linkage analyses of the hemicellulose showed that the accumulation of glucuronosyl arabinoxylan in bc5 nodes was perturbed by the mutation. The bc5 locus was narrowed to an approximately 3.1 Mb region of chromosome 2, where none of the other bc genes is located. The bc5 mutation appeared to reduce the expression levels of the OsCesA genes in the nodes after heading. The results indicate that the BC5 gene regulates the development of secondary cell walls of node sclerenchyma tissues.Plant and Cell Physiology 10/2009; 50(11):1886-97. · 4.70 Impact Factor -
Article: Involvement of arabinogalactan proteins in protonemata development from cultured cells of Marchantia polymorpha
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ABSTRACT: Arabinogalactan proteins (AGPs) are abundant plant cell-surface proteoglycans widely distributed in plant species. Crossed electrophoresis patterns of AGPs isolated from cultured cells before and after protonemata development differed, indicating that AGPs are involved in protonemata differentiation and development. Moreover, the addition of β-glucosyl Yariv reagent (βglcY), which binds specifically to AGPs, inhibits protonemata differentiation in cells of the liverwort Marchantia polymorpha L. cultured in protonemata-inducing medium. Transmission electron microscopic examination revealed that βglcY caused conspicuous disorder at the cell surface and the accumulation of abnormal structures between the plasma membrane and the cell wall. These results suggest that AGPs/βglcY complexes caused disturbances at the cell surface and inhibited cell-wall synthesis required for protonemata differentiation. Our results indicate that AGPs play a significant role in cell-wall synthesis during the protonemata-differentiation process of M. polymorpha.Physiologia Plantarum 09/2009; 124(4):504 - 514. · 3.11 Impact Factor -
Article: Intact carboxysomes in a cyanobacterial cell visualized by hilbert differential contrast transmission electron microscopy.
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ABSTRACT: Carboxysomes in rapidly frozen ice-embedded whole cells of the cyanobacterium Synechococcus sp. strain PCC 7942 were visualized by the recently developed Hilbert differential contrast transmission electron microscope. Structural details of carboxysomes were especially clearly visualized in the ruptured cells. The novel electron microscopy exhibited the paracrystalline arrays of molecules of the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase in the carboxysomes in much better contrast than conventional transmission electron microscopy with ultrathin sections of cells. The carboxysome was surrounded by a 5- to 6-nm-thick monolayer shell which consisted of orderly arrays of globular particles.Journal of Bacteriology 02/2006; 188(2):805-8. · 3.83 Impact Factor -
Article: Ultrastructural stability under high temperature or intensive light stress conferred by a small heat shock protein in cyanobacteria.
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ABSTRACT: The role and sub-cellular localization of the small heat shock protein HspA under stress conditions was investigated comparing the cyanobacterium Synechococcus strain ECT16-1, which constitutively expresses HspA, with the reference strain ECT. The ultrastructure of ECT cells under elevated temperature or intensive light stress exhibited severe damage including aggregation of cytosol and disordered thylakoid membranes, but in ECT16-1 cells these ultrastructural changes were much less conspicuous. Immunocytochemical studies showed that the main localization of HspA in the ECT16-1 cells shifted from the thylakoid area to the cytoplasm, then back to thylakoid area during the heat stress. Expression of HspA stabilized the morphology of nucleoids. The results are discussed, in particular with respect to the unique property of HspA to associate with thylakoid membranes.FEBS Letters 03/2005; 579(5):1235-42. · 3.54 Impact Factor -
Article: In vivo subcellular ultrastructures recognized with Hilbert differential contrast transmission electron microscopy.
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ABSTRACT: We describe the first application of a novel electron microscopic technique to visualize subcellular structures in a near-living state. Rapidly frozen ice-embedded cells provide the most realistic images, as they are free from artefacts induced by sample preparation methods, such as chemical fixation, dehydration, staining and sectioning. The application of the conventional transmission electron microscope to ice-embedded cell imaging, however, has been limited by the low image contrast. The recently developed Hilbert differential contrast transmission electron microscope, which exhibits an unexpectedly high contrast, akin to the differential interference contrast in visible light microscopy, enabled us to clearly discern detailed subcellular structures in ice-embedded cyanobacterial cells.Journal of Electron Microscopy 02/2005; 54(1):79-84. · 1.31 Impact Factor -
Article: Comparative analysis of the hspA mutant and wild-type Synechocystis sp. strain PCC 6803 under salt stress: evaluation of the role of hspA in salt-stress management.
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ABSTRACT: DNA microarray analysis has previously revealed that hspA, which encodes a small heat-shock protein, is the second most highly expressed gene under salt stress in Synechocystis sp. strain PCC 6803. Consequently, an hspA deletion mutant was studied under various salt stresses in order to identify a potential role of HspA in salt stress management. The mutant had a growth disadvantage under moderate salt stress. It lost the ability to develop tolerance to a lethal salt treatment by a moderate salt pre-treatment when the tolerance was evaluated by cell survival and the level of major soluble proteins, phycocyanins, while the wild-type acquired tolerance. Under various salt stresses, the mutant failed to undergo the ultrastructural changes characteristic of wild-type cells. The mutant, which showed higher survival than the wild-type after a direct shift to lethal salt conditions, accumulated higher levels of groESL1 and groEL2 transcripts and the corresponding proteins, GroES, GroEL1, and GroEL2, suggesting a role for these heat-shock proteins in conferring basal salt tolerance. Under salt stress, heat-shock genes, such as hspA, groEL2, and dnaK2, were transcriptionally induced and greatly stabilized, indicating a transcriptional and post-transcriptional mechanism of acclimation to salt stress involving these heat-shock genes.Archives of Microbiology 01/2005; 182(6):487-97. · 1.43 Impact Factor -
Article: Simple plunge freezing applied to plant tissues for capturing the ultrastructure close to the living state.
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ABSTRACT: In order to observe the ultrastructure close to the living state, simple plunge freezing in liquid propane was applied to plant tissues. The method yielded a well-preserved ultrastructure to a depth of up to 40 microm from the surface of the young pea leaves, which were used as the specimen. Within the well-frozen area all membranes appeared smooth and the ultrastructural details of each organelle were similar to those obtained by high-pressure freezing. Several physical connections between the membranes were visualized. The relative simplicity and the satisfactory freezing performance of the method render it suitable for capturing the features of actively functioning cells in routine ultrastructural studies.Journal of Electron Microscopy 02/2004; 53(6):677-80. · 1.31 Impact Factor -
Article: Ultrastructural implications of pretreatment for successful cryopreservation of Oncidium protocorm-like body.
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ABSTRACT: By applying pre-treatment with high concentrations of sucrose and glycerol prior to desiccation and subsequent freezing in liquid nitrogen, successful cryopreservation with high recovery rate was achieved in Oncidium PLB (protocorm-like body). Cellular and subcellular changes after each step in various cryopreservation regimes were examined to elucidate the mechanism of the beneficial effect of the pretreatment which confers resistance to desiccation and freezing.Cryo letters 26(5):333-40. · 1.25 Impact Factor
Top co-authors
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Institutions
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2010
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National Institute of Agrobiological Sciences
- Division of Plant Sciences
Tsukuba, Ibaraki-ken, Japan
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2004–2009
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Saitama University
- • Graduate School of Science and Engineering
- • Department of Biochemistry and Molecular Biology
- • Faculty of Science
Saitama, Saitama-ken, Japan
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