KEGG(Kyoto Encyclopedia of Genes and Genomes)〔和文〕 (特集 ゲノム医学の現在と未来--基礎と臨床) -- (データベース)

Stressful environments such as salinity, drought, and high temperature (heat) cause alterations in a wide range of physiological, biochemical, and molecular processes in plants. Photosynthesis, the most fundamental and intricate physiological process in all green plants, is also severely affected in all its phases by such stresses. Since the mechanism of photosynthesis involves various components, including photosynthetic pigments and photosystems, the electron transport system, and CO2 reduction pathways, any damage at any level caused by a stress may reduce the overall photosynthetic capacity of a green plant. Details of the stress-induced damage and adverse effects on different types of pigments, photosystems, components of electron transport system, alterations in the activities of enzymes involved in the mechanism of photosynthesis, and changes in various gas exchange characteristics, particularly of agricultural plants, are considered in this review. In addition, we discussed also progress made during the last two decades in producing transgenic lines of different C3 crops with enhanced photosynthetic performance, which was reached by either the overexpression of C3 enzymes or transcription factors or the incorporation of genes encoding C4 enzymes into C3 plants. We also discussed critically a current, worldwide effort to identify signaling components, such as transcription factors and protein kinases, particularly mitogen-activated protein kinases (MAPKs) involved in stress adaptation in agricultural plants.

Photosynthesis under stressful environments: An overview

To withstand the high intracellular pressure, the cell wall of most bacteria is stabilized by a unique cross-linked biopolymer called murein or peptidoglycan. It is made of glycan strands [poly-(GlcNAc-MurNAc)], which are linked by short peptides to form a covalently closed net. Completely surrounding the cell, the murein represents a kind of bacterial exoskeleton known as the murein sacculus. Not only does the sacculus endow bacteria with mechanical stability, but in addition it maintains the specific shape of the cell. Enlargement and division of the murein sacculus is a prerequisite for growth of the bacterium. Two groups of enzymes, hydrolases and synthases, have to cooperate to allow the insertion of new subunits into the murein net. The action of these enzymes must be well coordinated to guarantee growth of the stress-bearing sacculus without risking bacteriolysis. Protein-protein interaction studies suggest that this is accomplished by the formation of a multienzyme complex, a murein-synthesizing machinery combining murein hydrolases and synthases. Enlargement of both the multilayered murein of gram-positive and the thin, single-layered murein of gram-negative bacteria seems to follow an inside-to-outside growth strategy. New material is hooked in a relaxed state underneath the stress-bearing sacculus before it becomes inserted upon cleavage of covalent bonds in the layer(s) under tension. A model is presented that postulates that maintenance of bacterial shape is achieved by the enzyme complex copying the preexisting murein sacculus that plays the role of a template.

Growth of the Stress-Bearing and Shape-Maintaining Murein Sacculus of Escherichia coli

Teichoic acids (TAs) are major wall and membrane components of most gram-positive bacteria. With few exceptions, they are polymers of glycerol-phosphate or ribitol-phosphate to which are attached glycosyl and d-alanyl ester residues. Wall TA is attached to peptidoglycan via a linkage unit, whereas lipoteichoic acid is attached to glycolipid intercalated in the membrane. Together with peptidoglycan, these polymers make up a polyanionic matrix that functions in (i) cation homeostasis; (ii) trafficking of ions, nutrients, proteins, and antibiotics; (iii) regulation of autolysins; and (iv) presentation of envelope proteins. The esterification of TAs with d-alanyl esters provides a means of modulating the net anionic charge, determining the cationic binding capacity, and displaying cations in the wall. This review addresses the structures and functions of d-alanyl-TAs, the d-alanylation system encoded by the dlt operon, and the roles of TAs in cell growth. The importance of dlt in the physiology of many organisms is illustrated by the variety of mutant phenotypes. In addition, advances in our understanding of d-alanyl ester function in virulence and host-mediated responses have been made possible through targeted mutagenesis of dlt. Studies of the mechanism of d-alanylation have identified two potential targets of antibacterial action and provided possible screening reactions for designing novel agents targeted to d-alanyl-TA synthesis.

A Continuum of Anionic Charge: Structures and Functions of d-Alanyl-Teichoic Acids in Gram-Positive Bacteria

Most bacteria have multiple peptidoglycan hydrolases capable of cleaving covalent bonds in peptidoglycan sacculi or its fragments. An overview of the different classes of peptidoglycan hydrolases and their cleavage sites is provided. The physiological functions of these enzymes include the regulation of cell wall growth, the turnover of peptidoglycan during growth, the separation of daughter cells during cell division and autolysis. Specialized hydrolases enlarge the pores in the peptidoglycan for the assembly of large trans-envelope complexes (pili, flagella, secretion systems), or they specifically cleave peptidoglycan during sporulation or spore germination. Moreover, peptidoglycan hydrolases are involved in lysis phenomena such as fratricide or developmental lysis occurring in bacterial populations. We will also review the current view on the regulation of autolysins and on the role of cytoplasm hydrolases in peptidoglycan recycling and induction of β-lactamase.

Bacterial peptidoglycan (murein) hydrolases.

1: Introduction. 1.1. Plastid forms, their structural flexibility, and potential for transformation. 1.2. Chloroplast biogenesis: involvement of three plastid forms. 1.3. Design of the book and the limitations. 2: Proplastid to Chloroplast Transformation. 2.1. Development of internal membrane structures. 2.2. Thylakoid formation and pigment accumulation. 2.3. Biogenesis and assembly of light harvesting complex. 2.4. Assembly of individual thylakoid complexes. 2.5. Rubisco assembly. 2.6. Chloroplast protein targeting. 2.7. Temporal appearance of thylakoid complexes. 2.8. Factors regulating gene expression during chloroplast development. 2.9. Interorganellar communication, gene expression, and chloroplast development. 2.10. Environmental modulation of developing chloroplast. 3: Mature Chloroplast. 3.1. Chloroplast envelope. 3.2. The lamellae. 3.3. Light harvesting complexes. 3.4. Photosystems: composition, structural organization, and primary photochemistry. 3.5. Cytochrome b/f complex: the link between the photosystems. 3.6. ATP synthase: structure and mechanism of action. 3.7. The Calvin Benson cycle. 3.8. Other metabolic processes in mature chloroplast. 3.9. Chloroplast under stress. 4: Transformation of Chloroplast to Gerontoplast. 4.1. Introduction. 4.2. Senescence induced degradation of thylakoid proteins, loss of pigments, and ultrastructural changes of membranes. 4.3. Senescence induced changes in electron transport complexes and rubisco. 4.4. Chloroplast to gerontoplast transformation is accompanied by the changes in the pattern of gene expression of leaves. 4.5. Senescence signals and other regulating factors. 4.6. Stress response of the senescing leaves and modifications of gerontoplast. 5: Conclusion and the Future. 5.1. The picture of mechanisms of assembly of chloroplast complexes during development and their demolition during senescence is hazy. 5.2. The mechanisms of degradation of protein and chlorophyll during biogenesis of the organelle largely remain unclear. 5.3. Molecular biology of gerontoplast formation during leaf senescence, a challenging area of research for future. 5.4. The signalling systems associated with transformations of proplastid to chloroplast and chloroplast to gerontoplast are poorly understood. 5.5. Environmental modulation of chloroplast biogenesis is less known. 5.6. The study of chloroplast biogenesis needs better laboratory models. References. Abbreviations. Index.

Chloroplast Biogenesis: From Proplastid to Gerontoplast

A link between senescence-induced decline in photosynthesis and activity of β-glucosidase is examined in the leaves of Arabidopsis. The enzyme is purified and characterized. The molecular weight of the enzyme is 58 kDa. It shows maximum activity at pH 5.5 and at temperature of 50°C. Photosynthetic measurements and activity of the enzyme are conducted at different developmental stages including senescence of leaves. Senescence causes a significant loss in total chlorophyll, stomatal conductance, rate of evaporation and in the ability of the leaves for carbon dioxide fixation. The process also brings about a decline in oxygen evolution, quantum yield of photosystem II (PS II) and quantum efficiency of PS II photochemistry of thylakoid membrane. The loss in photosynthesis is accompanied by a significant increase in the activity of the cell wall-bound β-glucosidase that breaks down polysaccharides to soluble sugars. The loss in photosynthesis as a signal for the enhancement in the activity of the enzyme is confirmed from the observation that incubation of excised mature leaves in continuous dark or in light with a photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU) that leads to sugar starvation enhances the activity of the enzyme. The work suggests that in the background of photosynthetic decline, the polysaccharides bound to cell wall that remains intact even during late phase of senescence may be the last target of senescing leaves for a possible source of sugar for remobilization and completion of the energy-dependent senescence program.

Senescence‐induced loss in photosynthesis enhances cell wall β‐glucosidase activity

A model for the water splitting system of thylakoid membranes

Sulfur metabolism mediated modulation of plant response to various abiotic stress factors is the focus of this review. Since chloroplast is extremely sensitive to abiotic stress factors and at the same time a major location of sulfur assimilation, the organelle plays a major role in the modulation of stress response. The photosynthetic organelle coordinates carbon, nitrogen, and sulfur metabolic pathways and provides the essential precursors for synthesis of sulfur compounds. The abiotic stress factors like high light, low light, temperature extremes, drought, and UV radiations which the organelle experiences lead to creation of an oxidative environment and production of reactive oxygen species (ROS). Sulfur metabolites containing thiol residues with reversible oxidation-reduction potential effectively scavenge ROS in a series of biochemical reactions. Abiotic stress factors cause upand downregulations of several stress-related genes. The stress signals, their transmission, and downstream signaling network regulating gene expression are complex. The stress-induced redox signals generated in chloroplast play a major role in different signal transduction systems and expression of stress-responsive genes in green plants.

Response of Photosynthetic Organelles to Abiotic Stress: Modulation by Sulfur Metabolism

The anticancer studies of a Schiff base; (E)-2((2-hydroxybenzylidene)amino-3-mercaptopropanoic acid (H2L) (obtained from 2hydroxybenzaldehyde and L-cysteine) and its transition metal complexes have been reported. The evaluation of the growth inhibitory action was studied for the compounds against human colon carcinoma (HCT-116), human hepatocellular liver carcinoma (HEPG-2), normal melanocytes (HFB-4) and human breast carcinoma (MCF-7) cell lines. The obtained results revealed that the Schiff base and its chelates are active against human hepatocellular liver carcinoma (HEPG-2) cell lines. The powder X-ray diffraction analysis for the compounds was carried out through Phillips X’Pert High score software. The density functional theory computation for ligand and Co(II), Ni (II) and Cu(II) metal complexes were made to understand the mode of bonding by GAUSSIAN 03 rev. A.01 programme. The quantitative structure-activity relationship investigation was performed by using HyperChem Professional 8.0.3 software to understand the biological potency of the ligands. Moreover, a docking analysis using iGEMDOCKv2.1 software was carried out against the kinase enzyme PDB ID:1fvv.

Transition Metal Complexes of (E)‐2((2‐hydroxybenzylidene) amino‐3‐mercaptopropanoic acid: XRD, Anticancer, Molecular modeling and Molecular Docking Studies

Mukesh Kumar Raval

Papers

Chloroplast Biogenesis: From Proplastid to Gerontoplast

Senescence‐induced loss in photosynthesis enhances cell wall β‐glucosidase activity

A model for the water splitting system of thylakoid membranes

Response of Photosynthetic Organelles to Abiotic Stress: Modulation by Sulfur Metabolism

Transition Metal Complexes of (E)‐2((2‐hydroxybenzylidene) amino‐3‐mercaptopropanoic acid: XRD, Anticancer, Molecular modeling and Molecular Docking Studies