Paul Sabatier University

About: Paul Sabatier University is a education organization based out in Toulouse, France. It is known for research contribution in the topics: Population & Catalysis. The organization has 15431 authors who have published 23386 publications receiving 858364 citations.

Nod factors and a diffusible factor from arbuscular mycorrhizal fungi stimulate lateral root formation in Medicago truncatula via the DMI1/DMI2 signalling pathway.

Abstract: Legumes form two different types of intracellular root symbioses, with fungi and bacteria, resulting in arbuscular mycorrhiza and nitrogen-fixing nodules, respectively. Rhizobial signalling molecules, called Nod factors, play a key role in establishing the rhizobium-legume association and genes have been identified in Medicago truncatula that control a Nod factor signalling pathway leading to nodulation. Three of these genes, the so-called DMI1, DMI2 and DMI3 genes, are also required for formation of mycorrhiza, indicating that the symbiotic pathways activated by both the bacterial and the fungal symbionts share common steps. To analyse possible cross-talk between these pathways we have studied the effect of treatment with Nod factors on mycorrhization in M. truncatula. We show that Nod factors increase mycorrhizal colonization and stimulate lateral root formation. The stimulation of lateral root formation by Nod factors requires both the same structural features of Nod factors and the same plant genes (NFP, DMI1, DMI2, DMI3 and NSP1) that are required for other Nod factor-induced symbiotic responses such as early nodulin gene induction and cortical cell division. A diffusible factor from arbuscular mycorrhizal fungi was also found to stimulate lateral root formation, while three root pathogens did not have the same effect. Lateral root formation induced by fungal signal(s) was found to require the DMI1 and DMI2 genes, but not DMI3. The idea that this diffusible fungal factor might correspond to a previously hypothesized mycorrhizal signal, the 'Myc factor', is discussed.

Achieving few-femtosecond time-sorting at hard X-ray free-electron lasers

Abstract: Recently, few-femtosecond pulses have become available at hard X-ray free-electron lasers Coupled with the available sub-10 fs optical pulses, investigations into few-femtosecond dynamics are not far off However, achieving sufficient synchronization between optical lasers and X-ray pulses continues to be challenging We report a 'measure-and-sort' approach, which achieves sub-10 fs root-mean-squared (rms) error measurement at hard X-ray FELs, far beyond the 100-200 fs rms jitter limitations This timing diagnostic, now routinely available at the Linac Coherent Light Source (LCLS), is based on ultrafast free-carrier generation in optically transparent materials Correlation between two independent measurements enables unambiguous demonstration of ~6 fs rms error in reporting the optical/X-ray delay, with single shot error suggesting the possibility of reaching few-femtosecond resolution

Biochemistry and molecular biology of lignification

Abstract: SUMMARY Lignins, which result from the dehydrogenative polymerization of cinnamyl alcohols, are complex heteropolymers deposited in the walls of specific cells of higher plants. Lignins have probably been associated to land colonization by plants but several aspects concerning their biosynthesis, structure and function are still only partially understood. This review focuses on the modern physicochemical methods of structural analysis of lignins, and on the new approaches of molecular biology and genetic engineering applied to lignification. The principles, advantages and limitations of three important analytical tools for studying lignin structure are presented. They include carbon 13 nuclear magnetic resonance, analytical pyrolysis and thioacidolysis. The use of these methods is illustrated by several examples concerning the characterization of grass lignins,‘lignin-like’materials in protection barriers of plants and lignins produced by cell suspension cultures. Our present limited knowledge of the spatio temporal deposition of lignins during cell wall differentiation including the nature of the wall components associated to lignin deposition and of the cross-links between the different wall polymers is briefly reviewed. Emphasis is placed on the phenylpropanoid pathway enzymes and their corresponding genes which are described in relation to their potential roles in the quantitative and qualitative control of lignification. Recent findings concerning the promoter sequence elements responsible for the vascular expression of some of these genes are presented. A section is devoted to the enzymes specifically involved in the synthesis of monolignols: cinnamoyl CoA reductase and cinnamyl alcohol dehydrogenase. The recent characterization of the corresponding cDNAs/genes offers new possibilities for a better understanding of the regulation of lignification. Finally, at the level of the synthesis, the potential involvement of peroxidases and laccases in the polymerization of monolignols is critically discussed. In addition to previously characterized naturally occurring lignin mutants, induced lignin mutants have been obtained during the last years through genetic engineering. Some examples include plants transformed by O-methyltransferase and cinnamyl alcohol dehydrogenase antisense constructs which exhibit modified lignins. Such strategies offer promising perspectives in gaining a better understanding of lignin metabolism and functions and represent a realistic way to improve plant biomass.

The family of box ACA small nucleolar RNAs is defined by an evolutionarily conserved secondary structure and ubiquitous sequence elements essential for RNA accumulation.

Abstract: Eukaryotic cells contain a large number of small nucleolar RNAs (snoRNAs) A major family of snoRNAs features a consensus ACA motif positioned 3 nucleotides from the 3' end of the RNA In this study we have characterized nine novel human ACA snoRNAs (U64-U72) Structural probing of U64 RNA followed by systematic computer modeling of all known box ACA snoRNAs revealed that this class of snoRNAs is defined by a phylogenetically conserved secondary structure The ACA snoRNAs fold into two hairpin structures connected by a single-stranded hinge region and followed by a short 3' tail The hinge region carries an evolutionarily conserved sequence motif, called box H (consensus, AnAnnA) The H box, probably in concert with the flanking helix structures and the ACA box characterized previously, plays an essential role in the accumulation of human U64 intronic snoRNA The correct processing of a yeast ACA snoRNA, snR36, in mammalian cells demonstrated that the cis- and trans-acting elements required for processing and accumulation of ACA snoRNAs are evolutionarily conserved The notion that ACA snoRNAs share a common secondary structure and conserved box elements that likely function as binding sites for common proteins (eg, GAR1) suggests that these RNAs possess closely related nucleolar functions

Nonsmooth H ∞ synthesis

Abstract: We develop nonsmooth optimization techniques to solve H∞ synthesis problems under additional structural constraints on the controller. Our approach avoids the use of Lyapunov variables and therefore leads to moderate size optimization programs even for very large systems. The proposed framework is very versatile and can accommodate a number of challenging design problems including static, fixed-order, fixed-structure, decentralized control, design of PID controllers and simultaneous design and stabilization problems. Our algorithmic strategy uses generalized gradients and bundling techniques suited for the H∞-norm and other nonsmooth performance criteria. Convergence to a critical point from an arbitrary starting point is proved (full version) and numerical tests are included to validate our methods.