2.0 rCF based composite materials: manufacturing processes and mechanical properties

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Identification et caractérisation de laccases impliquées dans la polymérisation des monolignols chez la plante modèle Arabidopsis thaliana

Alors qu'il est établi que les peroxydases sont impliquées dans la polymérisation des précurseurs de lignine, le rôle des laccases (EC 1.10.3.2) dans la lignification constitutive reste énigmatique. Nous avons étudié des mutants d'insertion de l'ADN-T d'Arabidopsis thaliana. Dans un premier temps, deux gènes (AtLAC4 et AtLAC17) fortement exprimés dans les tiges ont été identifiés. AtLAC17 s'exprime spécifiquement dans les fibres interfasciculaires et AtLAC4 s'exprime dans les vaisseaux et les fibres interfasciculaires. Nous avons produit deux doubles mutants, kim et snips, par croisement des mutants pour les gènes AtLAC17 (lac17) et AtLAC4 (irx12 et lac4g). Les simples et doubles mutants présentent une croissance normale, à l'exception de snips qui est parfois semi-nain et possèdent des vaisseaux collapsés. Si les simples mutants présentent une diminution modérée de leur teneur en lignine, les tiges de kim (irx12 x lac17) et snips (lac4g x lac17) ont un contenu réduit de 20% et 40% respectivement. Cette diminution de teneur en lignine conduit à un meilleur rendement de saccharification. Des thioacidolyses révèlent que l'absence d'activité AtLAC17 se répercute principalement sur le dépôt des unités G dans les fibres interfasciculaires et la complémentation du mutant lac17 avec la séquence de AtLAC17 restaure un profil de lignification normal. Cette étude met en évidence que AtLAC4 et AtLAC17 sont toutes deux impliquées dans la lignification constitutive des tiges d'Arabidopsis et que l'absence de AtLAC17 a un impact sur la polymérisation des unités G spécifiquement au niveau des fibres, suggérant un rôle dans les étapes précoces de la lignification.While it is established that peroxidases are involved in the polymerization of lignin precursors, it is not yet clear whether laccases (EC 1.10.3.2) participate to constitutive lignification. ln order to address this issue, we studied laccase T-DNA insertion mutants in Arabidopsis thaliana. We first identified two genes, AtLAC4 and AtLAC17, highly expressed in stems. AtLAC17was specifically expressed in the interfascicular fibers while AtLAC4 was expressed in vascular bundles and interfascicular fibers. We produced two double mutants, kim and snips, by crossing the AtLAC17 (lac17) mutant with two AtLAC4 mutants (named irx12 and lac4g). The single and double mutants displayed normal growth, except snips, which sometimes had a semi-dwarf phenotype and collapsed vessels. While the single mutants had moderately reduced lignin levels, the stems of kim (irx12 x lac17) and snips (lac4g x lac17) displayed lignin content reduced by 20% and 40%, respectively. This lower lignin level improved their saccharification yield. Thioacidolysis revealed that disrupting AtLAC17 mainly affected the deposition of G lignin units in the interfascicular fibers and that complementation of lac17 with AtLAC17 restored the normal lignin profile. This study provides evidence that both AtLAC4 and AtLAC17 contribute to the constitutive lignification of Arabidopsis stems and that AtLAC17 is involved in the deposition of G lignin units in fibers, a specificity, which suggests a role at the early lignification stage.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Crystallization and preliminary structural analysis of catalase A from Saccharomyces cerevisiae

International audienceYeast peroxisomal catalase A, obtained at high yields by over expression of the C-terminally modified gene from a 2 mu-plasmid, has been crystallized in a form suitable for high resolution X-ray diffraction studies. Brownish crystals with bipyrimidal morphology and reaching ca. 0.8 mm in size were produced by the hanging drop method using ammonium sulphate as precipitant. These crystals diffract better than 2.0 A resolution and belong to the hexagonal space group P6(1)22 with unit cell parameters a = b = 184.3 A and c = 305.5 A. An X-ray data set with 76% completeness at 3.2 A resolution was collected in a rotating anode generator using mirrors to improve the collimation of the beam. An initial solution was obtained by molecular replacement only when using a beef liver catalase tetramer model in which fragments with no sequence homology had been omitted, about 150 residues per subunit. In the structure found a single molecule of catalase A (a tetramer with accurate 222 molecular symmetry) is located in the asymmetric unit of the crystal with an estimated solvent content of about 61%. The preliminary analysis of the structure confirms the absence of a carboxy terminal domain as the one found in the catalase from Penicillium vitalae, the only other fungal catalase structure available. The NADPH binding site appears to be involved in crystal contacts, suggesting that heterogeneity in the occupancy of the nucleotide can be a major difficulty during crystallization

Using steam thermolysis to recycle carbon fibres from composite waste

International audienceIn this article, Alpha Recyclage Composites presents a new steam thermolysis process to treat carbon fibre composites for recycling. The thermochemical process is used to recover the carbon fibres, which are then recycled into new thermoplastic composites. These second-generation materials possess mechanical properties that are comparable to those of materials made using virgin carbon fibre

Role of Endoproteolytic Processing in the Adhesive and Signaling Functions of αvβ5 Integrin

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2.0 rCF based composite materials: manufacturing processes and mechanical properties

International audienc

Lignin polymerization in Arabidopsis and poplar

International audienceLignin is a major component of the secondary cell wall. This complex phenolic polymer is derived mainly from three hydroxycinnamyl alcohol monomers named monolignols. After transport of the monolignols to the cell wall, lignin is formed through an enzymatically-initiated oxidative polymerization of these precursors. Whereas many studies have established that this polymerization involves peroxidases, the involvement of laccases is more speculative. The identification of the peroxidases and laccases specifically involved in lignification is complicated by the fact that these enzymes belong to multigene families. For instance, in Arabidopsis, there are 73 peroxidase and 17 laccase genes. In order to determine which peroxidases and/or laccases could be involved in the polymerisation of monolignols, several strategies have been considered: • Expression profiling in the highly lignified infloresecence stem by RT-PCR and promoter/GUS fusions • Presence in the cell wall proteome of stems • Characterization of homozygous knock-out Arabidopsis TDNA mutants and determination of the impact of the mutation on lignin content and composition. The results of this study will be presented and new information on the importance of several genes in lignification will be provided. Orthologs of poplar have been identified and are currently under study