Molecular regulation of starch metabolism

Starch is the second most abundant biomass next to cellulose and composed of amylopectin, a highly branched glucan, and amylose, an essentially linear glucan. The former and the latter glucans usually account for approximately 65–85% and 15–35% of the total starch, respectively. During the last three decades the basic scheme of starch biosynthesis has been established based on numerous biochemical, genetic, and molecular biological approaches worldwide using a variety of higher plants and algae. It is well known that after the synthesis of ADPglucose by ADPglucose pyrophosphorylase (AGPase), amylopectin’s fne structure is formed by concerted actions of multiple isozymes from three classes of enzymes, starch synthase (SS), starch branching enzyme (BE), and starch debranching enzyme (DBE), and that amylose is synthesized by mainly granule-bound SS (GBSS). In addition to the roles of starch biosynthetic isozymes, the contributions of α-glucan phosphorylase, α-glucan, water dikinase, phosphoglucan, water dikinase, pyruvate, phosphate dikinase, α-amylase, and carbohydrate-binding modules have been documented. Information on the whole genome sequence and omics analyses are available in main plant species. All these results revealed the roles of key biosynthetic isozymes of SS, GBSS, BE, and DBE and subunits of AGPase to starch biosynthesis, and presently we know to what extent the fne structure of starch molecules and the internal structure and physicochemical properties of starch granules as well as starch amounts can be modifed in accord with the activity levels of these isozymes and subunits. However, in spite of numerous past investigations, the regulation of the network of enzymatic reactions has not been fully understood. To resolve the complex mechanisms, we need to examine several topics such as redundancy and supplementary functions of multiple isozymes, enzymeenzyme interaction(s), and regulatory factors controlling catalytic and specific activities of individual isozymes, temporal and spatial co-expression of multiple isozymes, post-translational modifcation of enzymatic capacities such as phosphorylation, glycosylation, and redox state. There are still lots of uncertainties in the understanding of the initiation of starch biosynthesis.Fil: Nakamura, Yasunori. Akita Prefectural University; JapónFil: Steup, Martin. Universitat Potsdam; AlemaniaFil: Colleoni, Christophe. Université de Lille; FranciaFil: Iglesias, Alberto Alvaro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; ArgentinaFil: Bao, Jinsong. Zhejiang University; ChinaFil: Fujita, Naoko. University of Guelph; CanadáFil: Tetlow, Ian. University of Guelph; Canad

Retracing Storage Polysaccharide Evolution in Stramenopila

Eukaryotes most often synthesize storage polysaccharides in the cytosol or vacuoles in the form of either alpha (glycogen/starch)- or beta-glucosidic (chrysolaminarins and paramylon) linked glucan polymers. In both cases, the glucose can be packed either in water-soluble (glycogen and chrysolaminarins) or solid crystalline (starch and paramylon) forms with different impacts, respectively, on the osmotic pressure, the glucose accessibility, and the amounts stored. Glycogen or starch accumulation appears universal in all free-living unikonts (metazoa, fungi, amoebozoa, etc.), as well as Archaeplastida and alveolata, while other lineages offer a more complex picture featuring both alpha- and beta-glucan accumulators. We now infer the distribution of these polymers in stramenopiles through the bioinformatic detection of their suspected metabolic pathways. Detailed phylogenetic analysis of key enzymes of these pathways correlated to the phylogeny of Stramenopila enables us to retrace the evolution of storage polysaccharide metabolism in this diverse group of organisms. The possible ancestral nature of glycogen metabolism in eukaryotes and the underlying source of its replacement by beta-glucans are discussed

Kre6 (yeast 1,6-β-transglycosylase) homolog, PhTGS, is essential for β-glucan synthesis in the haptophyte Pleurochrysis haptonemofera

Haptophytes synthesize unique β-glucans containing more β-1,6-linkages than β-1,3 linkages, as a storage polysaccharide. To understand the mechanism of the synthesis, we investigated the roles of Kre6 (yeast 1,6-β-transglycosylase) homologs, PhTGS, in the haptophyte Pleurochrysis haptonemofera. RNAi of PhTGS repressed β-glucan accumulation and simultaneously induced lipid production, suggesting that PhTGS is involved in β-glucan synthesis and that the knockdown leads to the alteration of the carbon metabolic flow. PhTGS was expressed more in light, where β-glucan was actively produced by photosynthesis, than in the dark. The crude extract of E. coli expressing PhKre6 demonstrated its activity to incorporate 14C-UDP-glucose into β-glucan of P. haptonemofera. These findings suggest that PhTGS functions in storage β-glucan synthesis specifically in light, probably by producing the β-1,6-branch

Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network

Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Étude du métabolisme de l'amidon chez les Archaeplastida (le cas de l'algue glaucophyte modèle unicellulaire Cyanophora paradoxa et de l'algue rouge multicellulaire Chondrus crispus)

L'amidon et le glycogène définissent les deux polysaccharides de réserve les plus répandus dans le monde vivant. L'apparition de l'amidon chez les eucaryotes coïncide avec un événement d'endosymbiose unique qui s'est déroulé il y a 1,6 milliards d'années entre une cyanobactérie et un eucaryote primitif. De cet événement sont apparues trois lignées photosynthétiques : les Chloroplastida (plantes terrestres et algues vertes), les Rhodophyceae (algues rouges et organismes qui en sont dérivés par endosymbiose secondaire) et les Glaucophyta. La voie de biosynthèse de l'amidon chloroplastique chez les Chloroplastida est relativement bien caractérisée. Pour celle des Rhodophyceae (amidon cytoplasmique) des études ont déjà été entreprises mais les informations obtenues sont encore incomplètes et non représentatives de la lignée en général. Enfin pour les Glaucophyta, qui ont divergé de façon plus précoce après l'évènement d'endosymbiose aucune information sur le métabolisme de son amidon (cytoplasmique) n'était disponible. Afin d'appréhender la voie de biosynthèse utilisée par ces organismes nous avons entrepris la caractérisation de la voie métabolique de l'amidon de Cyanophora paradoxa (Glaucophyta) ainsi que celle de Chondrus crispus (Rhodophyceae). Ce manuscrit de thèse présente essentiellement des informations sur le métabolisme de l'amidon floridéen chez Cyanophora paradoxa, l'étude entreprise chez Chondrus crispus étant encore à l'état préliminaire.Starch and glycogen both define the most wide-spread storage polysaccharide in the world. The starch appearance in the eukaryotic lineage coincides with a single endosymbiotic event occurring 1,6 billion years ago between a cyanobacteria and a primitive eukaryotic hosto From this event appeared three photosynthetic lines: Chloroplastida (land plants and green algae), Rhodophyceae (red algae and organisms which are diverted from the Rhodophyceae by secondary endosymbiosis) and Glaucophyta. The plastid starch biosynthesis pathway in Chloroplastida is relatively weIl characterized. For the Rhodophyceae (cytosolic starch) studies have already been initiated but the information obtained is still incomplete and not representative of the lineage. Finally for the Glaucophyta, which diverged in a more premature way after the event of endosymbiosis no information about this (cytosolic) starch metabolism was available. To discover the biosynthesis pathway used by these organisms, we decided to perform the complete characterization of the starch biosynthetic pathway for two differents organisms: The Glaucophyta named Cyanophora paradoxa and the Rhodophyceae named Chondrus crispus. This manuscript of PhD mainly presents information on the Floridian starch metabolism of Cyanophora paradoxa. The starch characterisation of Chondrus crispus is currently at the preliminary stage and will require further development.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF