Search

SUMMARYIn multicellular systems, all cells exhibit transcriptional noise. However, its exact contribution to morphogenesis often remains unclear, especially in animals where cells can also move. Here we take advantage of walled plant cells, where transcriptional noise happens in tissues with a fixed topology. Using synchronously growing guard cells in stomata, we demonstrate that mutation in VIP3, a subunit of the conserved polymerase-associated factor 1 complex (Paf1C), increases transcriptional noise in Arabidopsis. This conclusion could be generalized to other group of cells at the shoot apex. Such noise translates into growth and shape defects. Indeed, in vip3 sepals, we measured higher growth heterogeneity between adjacent cells, with molecular evidence of increased local mechanical conflicts. This even culminated with the presence of negatively growing cells in specific growth conditions. Interestingly, such increased local noise makes the regional pattern of growth less clear-cut. Reduced regional conflicts lead to delay in organ growth arrest, ultimately making final organ shapes and sizes more variable. We propose that transcriptional noise is managed by Paf1C to ensure organ robustness by building up mechanical conflicts at the regional scale, instead of the local scale.HIGHLIGHTSPaf1C controls transcriptional noise in ArabidopsisPaf1C reduces growth heterogeneity and dampens local mechanical conflictsImpairing both Paf1C and microtubules can trigger negative growth in ArabidopsisScaling up local conflicts to regional ones with sharp boundaries contributes to organ shape robustness

To survive, cells must constantly resist mechanical stress. In plants, this involves the reinforcement of cell walls, notably through microtubule-dependent cellulose deposition, and thus wall sensing. Several receptor-like kinases have been proposed to act as mechanosensors. Here we tested whether the microtubule response to stress acts downstream of known wall sensors. Using a multi-step screen with eleven mutant lines, we identify FERONIA as the primary candidate for controlling the microtubule response to stress. However, when performing mechanical perturbations, we show that the microtubule response to stress can be independent from FER. We reveal that the feronia phenotype can be partially rescued by reducing tensile stress levels. Conversely, in the absence of both microtubules and FER, cells swell and burst like soap bubbles. Altogether, this shows that the microtubule response to stress acts as an independent pathway to resist stress, in parallel to FER. We propose that both pathways are key components to turn plant cells from passive to active material.

Four marine bacterial strains were isolated from a thallus of the brown alga Ascophyllum nodosum collected in Roscoff, France. Cells were Gram-stain-negative, strictly aerobic, non-flagellated, gliding, rod-shaped and grew optimally at 25–30 °C, at pH 7–8 and with 2–4 % NaCl. Phylogenetic analyses of their 16S rRNA gene sequences showed that the bacteria were affiliated to the genus Zobellia (family Flavobacteriaceae , phylum Bacteroidetes ). The four strains exhibited 97.8–100 % 16S rRNA gene sequence similarity values among themselves, 97.9–99.1 % to the type strains of Zobellia amurskyensis KMM 3526T and Zobellia laminariae KMM 3676T, and less than 99 % to other species of the genus Zobellia . The DNA G+C content of the four strains ranged from 36.7 to 37.7 mol%. Average nucleotide identity and digital DNA–DNA hybridization calculations between the new strains and other members of the genus Zobellia resulted in values of 76.4–88.9 % and below 38.5 %, respectively. Phenotypic, phylogenetic and genomic analyses showed that the four strains are distinct from species of the genus Zobellia with validly published names. They represent two novel species of the genus Zobellia , for which the names Zobellia roscoffensis sp. nov. and Zobellia nedashkovskayae sp. nov. are proposed with Asnod1-F08T (RCC6906T=KMM 6823T=CIP 111902T) and Asnod2-B07-BT (RCC6908T=KMM 6825T=CIP 111904T), respectively, as the type strains.

The shoot apical meristem (SAM) gives rise to all aerial organs of the plant. The cell walls are supposed to play a central role in this process, translating molecular regulation into dynamic changes of growth rates and directions, although their precise role in morphogenesis during organ formation remains not well understood. Here we investigate the role of xyloglucans (XyGs), which form a major, yet functionally poorly characterized, wall component in the SAM. Using immunolabeling, biochemical analysis, genetic approaches, micro-indentation, laser ablations and live imaging, we show that XyGs are important for meristem shape and phyllotaxis, although no difference in cell wall stiffness could be observed when XyGs are perturbed. Mutations in enzymes required for XyG synthesis also affect other cell wall components such as cellulose content and the pectin methylation status. Interestingly, we show that the control of cortical microtubules dynamics by the severing enzyme KATANIN becomes vital when XyGs are perturbed or absent. This suggests an active role of the cytoskeleton in compensating for altered wall composition.

A major challenge in plant systems biology is the development of robust, predictive multiscale models for organ growth. In this context it is important to bridge the gap between the, rather well-documented molecular scale and the organ scale by providing quantitative methods to study within-organ growth patterns. Here, we describe a simple method for the analysis of the evolution of growth patterns within rod-shaped organs that does not require adding markers at the organ surface. The method allows for the simultaneous analysis of root and hypocotyl growth, provides spatio-temporal information on curvature, growth anisotropy and relative elemental growth rate and can cope with complex organ movements. We demonstrate the performance of the method by documenting previously unsuspected complex growth patterns within the growing hypocotyl of the model species Arabidopsis thaliana during normal growth, after treatment with a growth-inhibiting drug or in a mechano-sensing mutant. The method is freely available as an intuitive and user-friendly Matlab application called KymoRod.

International audience; The shoot apical meristem (SAM) gives rise to all aerial plant organs. Cell walls are thought to play a central role in this process, translating molecular regulation into dynamic changes in growth rate and direction, although their precise role in morphogenesis during organ formation is poorly understood. Here, we investigated the role of xyloglucans (XyGs), a major, yet functionally poorly characterized, wall component in the SAM of Arabidopsis (Arabidopsis thaliana). Using immunolabeling, biochemical analysis, genetic approaches, microindentation, laser ablation, and live imaging, we showed that XyGs are important for meristem shape and phyllotaxis. No difference in the Young's modulus (i.e. an indicator of wall stiffness) of the cell walls was observed when XyGs were perturbed. Mutations in enzymes required for XyG synthesis also affect other cell wall components such as cellulose content and pectin methylation status. Interestingly, control of cortical microtubule dynamics by the severing enzyme KATANIN became vital when XyGs were perturbed or absent. This suggests that the cytoskeleton plays an active role in compensating for altered cell wall composition.

Le Pôle France rassemble une sélection de futurs rugbymen professionnels pour une année d’entraînement intensif. Cet article propose une étude de cas autour de deux « instruments » intégrés à la formation des pensionnaires du Pôle France : un robot, et l’image vidéo. L’observation de l’utilisation du simulateur de mêlée amène à analyser la mise en scène du geste technique en situation d’entraînement. La manière dont la vidéo est intégrée au quotidien de la formation pose la question du rôle de l’image dans l’apprentissage, tel qu’il est conçu par les entraîneurs, et reçu par les joueurs. Dans les deux cas est explorée une communauté hybride homme-machine aux modalités particulières, au service de la formation technique sportive de haut niveau. The Pôle France brings together a selection of future professional rugby players for an intensive training year. This article presents a case study on two "instruments" used during trainings: robots, and video recordings. The scrum simulator is used to analyze how rugby players’ technical gesture is staged during trainings. The way video recordings are integrated into daily training raises the question of the role of images in the learning process as developped and taught by coaches, and learned by players. In both cases, a man-human hybrid community is described as part of the high performance sport technics training.

Antagonistic growth effects of two T-DNA alleles in THESEUS1 correlate with the expression of a predicted functional THE1 protein lacking the kinase domain and antisense transcripts, respectively., Perturbation of cellulose synthesis in plants triggers stress responses, including growth retardation, mediated by the cell wall integrity-sensing receptor-like kinase (RLK) THESEUS1 (THE1). The analysis of two alleles carrying T-DNA insertions at comparable positions has led to conflicting conclusions concerning the impact of THE1 signaling on growth. Here we confirm that, unlike the1-3 and other the1 alleles in which cellular responses to genetic or pharmacological inhibition of cellulose synthesis are attenuated, the1-4 showed enhanced responses, including growth inhibition, ectopic lignification, and stress gene expression. Both the1-3 and the1-4 express a transcript encoding a predicted membrane-associated truncated protein lacking the kinase domain. However, the1-3, in contrast to the1-4, strongly expresses antisense transcripts, which are expected to prevent the expression of the truncated protein as suggested by the genetic interactions between the two alleles. Seedlings overexpressing such a truncated protein react to isoxaben treatment similarly to the1-4 and the full-length THE overexpressor. We conclude that the1-4 is a hypermorphic allele; that THE1 signaling upon cell wall damage has a negative impact on cell expansion; and that caution is required when interpreting the phenotypic effects of T-DNA insertions in RLK genes.

International audience; The growth of plants, like that of other walled organisms, depends on the ability of the cell wall to yield without losing its integrity. In this context, plant cells can sense the perturbation of their walls and trigger adaptive modifications in cell wall polymer interactions. Catharanthus roseus receptor-like kinase 1-like (CrRLK1L) THESEUS1 (THE1) was previously shown in Arabidopsis to trigger growth inhibition and defense responses upon perturbation of the cell wall, but so far, neither the ligand nor the role of the receptor in normal development was known. Here, we report that THE1 is a receptor for the peptide rapid alkalinization factor (RALF) 34 and that this signaling module has a role in the fine-tuning of lateral root initiation. We also show that RALF34-THE1 signaling depends, at least for some responses, on FERONIA (FER), another RALF receptor involved in a variety of processes, including immune signaling, mechanosensing, and reproduction [1]. Together, the results show that RALF34 and THE1 are part of a signaling network that integrates information on the integrity of the cell wall with the coordination of normal morphogenesis.

International audience; Alga-associated microorganisms, in the context of their numerous interactions with the host and the complexity of the marine environment, are known to produce diverse hydrolytic enzymes with original biochemistry. We recently isolated several macroalgal-polysaccharide-degrading bacteria from the surface of the brown alga Ascophyllum nodosum. These active isolates belong to two classes: the Flavobacteriia and the Gammaproteobacteria. In the present study, we constructed two "plurigenomic" (with multiple bacterial genomes) libraries with the 5 most interesting isolates (regarding their phylogeny and their enzymatic activities) of each class (Fv and Gm libraries). Both libraries were screened for diverse hydrolytic activities. Five activities, out of the 42 identified in the natural polysaccharolytic isolates, were recovered by functional screening: a xylanase (GmXyl7), a beta-glucosidase (GmBg1), an esterase (GmEst7) and two iota-carrageenases (Fvi2.5 and Gmi1.3). We discuss here the potential role of the used host-cell, the average DNA insert-sizes and the used restriction enzymes on the divergent screening yields obtained for both libraries and get deeper inside the “great screen anomaly”. Interestingly, the discovered esterase probably stands for a novel family of homoserine o-acetyltransferase-like-esterases, while the two iota-carrageenases represent new members of the poorly known GH82 family (containing only 19 proteins since its description in 2000). These original results demonstrate the efficiency of our uncommon “plurigenomic” library approach and the underexplored potential of alga-associated cultivable microbiota for the identification of novel and algal-specific enzymes.

Bacteria degrading algal polysaccharides are key players in the global carbon cycle and in algal biomass recycling. Yet the water column, which has been studied largely by metagenomic approaches, is poor in such bacteria and their algal-polysaccharide-degrading enzymes. Even more surprisingly, the few published studies on seaweed-associated microbiomes have revealed low abundances of such bacteria and their specific enzymes. However, as macroalgal cell-wall polysaccharides do not accumulate in nature, these bacteria and their unique polysaccharidases must not be that uncommon. We, therefore, looked at the polysaccharide-degrading activity of the cultivable bacterial subpopulation associated with Ascophyllum nodosum. From A. nodosum triplicates, 324 bacteria were isolated and taxonomically identified. Out of these isolates, 78 (~25%) were found to act on at least one tested algal polysaccharide (agar, ?- or ?-carrageenan, or alginate). The isolates “active” on algal-polysaccharides belong to 11 genera: Cellulophaga, Maribacter, Algibacter, and Zobellia in the class Flavobacteriia (41) and Pseudoalteromonas, Vibrio, Cobetia, Shewanella, Colwellia, Marinomonas, and Paraglaceciola in the class Gammaproteobacteria (37). A major part represents likely novel species. Different proportions of bacterial phyla and classes were observed between the isolated cultivable subpopulation and the total microbial community previously identified on other brown algae. Here, Bacteroidetes and Gammaproteobacteria were found to be the most abundant and some phyla (as Planctomycetes and Cyanobacteria) frequently encountered on brown algae weren't identified. At a lower taxonomic level, twelve genera, well-known to be associated with algae (with the exception for Colwellia), were consistently found on all three A. nosodum samples. Even more interesting, 9 of the 11 above mentioned genera containing polysaccharolytic isolates were predominant in this common core. The cultivable fraction of the bacterial community associated with A. nodosum is, thus, significantly enriched in macroalgal-polysaccharide-degrading bacteria and these bacteria seem important for the seaweed holobiont even though they are under-represented in alga-associated microbiome studies.

Plant lignocellulosic biomass, mostly composed of cell walls, is one of the largest, mostly untapped, reserves of renewable carbon feedstock on the planet. Energy-rich polysaccharide polymers of plant cell walls can be broken down to produce fermentable sugars used to produce bioethanol. However, the complex structure of plant cell walls, and in particular, the presence of lignin, makes them recalcitrant to enzymatic degradation. Reducing this recalcitrance represents a major technological challenge. Brachypodium distachyon is an excellent model to identify parameters underlying biomass quality of energy grasses. In this work, we identified a mutant line spa1 with a so far undescribed phenotype combining brittleness with increased elasticity of the internodes. Mutant cell walls contain less crystalline cellulose and changes in hemicellulose and lignin quality and quantity. Using a dedicated reactor to follow in real-time, the evolution of straw particle size and sugar release during enzymatic digestion, we show that, despite the increased lignin content, the spa1 mutant has a dramatic reduced recalcitrance to saccharification compared to the WT. These observations demonstrate that other parameters besides lignin content are relevant for the improvement of biomass recalcitrance in energy grasses.

International audience; Marine microorganisms play key roles in every marine ecological process, hence the growing interest in studying their populations and functions. Microbial communities on algae remain underexplored, however, despite their huge biodiversity and the fact that they differ markedly from those living freely in seawater. The study of this microbiota and of its relationships with algal hosts should provide crucial information for ecological investigations on algae and aquatic ecosystems. Furthermore, because these microorganisms interact with algae in multiple, complex ways, they constitute an interesting source of novel bioactive compounds with biotechnological potential, such as dehalogenases, antimicrobials, and alga-specific polysaccharidases (e.g., agarases, carrageenases, and alginate lyases). Here, to demonstrate the huge potential of alga-associated organisms and their metabolites in developing future biotechnological applications, we first describe the immense diversity and density of these microbial biofilms. We further describe their complex interactions with algae, leading to the production of specific bioactive compounds and hydrolytic enzymes of biotechnological interest. We end with a glance at their potential use in medical and industrial applications.

A metagenomic library was constructed from microorganisms associated with the brown alga Ascophyllum nodosum . Functional screening of this library revealed 13 novel putative esterase loci and two glycoside hydrolase loci. Sequence and gene cluster analysis showed the wide diversity of the identified enzymes and gave an idea of the microbial populations present during the sample collection period. Lastly, an endo-β-1,4-glucanase having less than 50% identity to sequences of known cellulases was purified and partially characterized, showing activity at low temperature and after prolonged incubation in concentrated salt solutions.

Le bois de tension (BT) est produit par les arbres feuillus en réponse à des contraintes mécaniques. Il présente des caractéristiques anatomiques, physico-chimiques et mécaniques particulières qui confèrent aux arbres un potentiel d’adaptation vis-à-vis de la contrainte subie. Traditionnellement dans la production de bois d’oeuvre, sa présence en trop grande proportion dans les grumes est une caractéristique indésirable car elle peut induire des déformations ou des fentes importantes des sciages. Néanmoins, comme le bois de tension se caractérise par une très faible teneur en lignine et une forte teneur en cellulose, il présente un intérêt pour une valorisation du bois en bioéthanol de 2ème génération. Quelle que soit la valorisation envisagée, il apparait crucial de pouvoir quantifier la teneur en bois de tension dans le bois. Cependant, les techniques actuelles, principalement basées sur de la coloration différentielle, de l’analyse histologique ou une inspection visuelle (Badia et al., 2005), sont couteuses et laborieuses, et de fait elles ne permettent pas d’évaluer cette propriété dans un nombre important d’échantillons. La spectrométrie infrarouge est une technique à haut-débit prometteuse pour évaluer les propriétés physico-chimiques du bois. Sa mise en oeuvre nécessite la construction préalable d’un modèle de calibration pour la propriété ciblée. Comme le bois de tension présente des propriétés physico-chimiques particulières, l’évaluation de sa teneur dans un échantillon de bois doit être possible par spectrométrie infrarouge. L’objectif de cette étude est de tester cette hypothèse sur des échantillons de peuplier et à partir d’une gamme de pourcentage de BT artificiellement créée.