KATANIN-dependent mechanical properties of the stigmatic cell wall mediate the pollen tube path in Arabidopsis.

Successful fertilization in angiosperms depends on the proper trajectory of pollen tubes through the pistil tissues to reach the ovules. Pollen tubes first grow within the cell wall of the papilla cells, applying pressure to the cell. Mechanical forces are known to play a major role in plant cell shape by controlling the orientation of cortical microtubules (CMTs), which in turn mediate deposition of cellulose microfibrils (CMFs). Here, by combining imaging, genetic and chemical approaches, we show that isotropic reorientation of CMTs and CMFs in aged Col-0 and katanin1-5 (ktn1-5) papilla cells is accompanied by a tendency of pollen tubes to coil around the papillae. We show that this coiled phenotype is associated with specific mechanical properties of the cell walls that provide less resistance to pollen tube growth. Our results reveal an unexpected role for KTN1 in pollen tube guidance on the stigma by ensuring mechanical anisotropy of the papilla cell wall

SYNERGISTIC ON AUXIN AND CYTOKININ 1 positively regulates growth and attenuates soil pathogen resistance

Plants as non-mobile organisms constantly integrate varying environmental signals to flexibly adapt their growth and development. Local fluctuations in water and nutrient availability, sudden changes in temperature or other abiotic and biotic stresses can trigger changes in the growth of plant organs. Multiple mutually interconnected hormonal signaling cascades act as essential endogenous translators of these exogenous signals in the adaptive responses of plants. Although the molecular backbones of hormone transduction pathways have been identified, the mechanisms underlying their interactions are largely unknown. Here, using genome wide transcriptome profiling we identify an auxin and cytokinin cross-talk component; SYNERGISTIC ON AUXIN AND CYTOKININ 1 (SYAC1), whose expression in roots is strictly dependent on both of these hormonal pathways. We show that SYAC1 is a regulator of secretory pathway, whose enhanced activity interferes with deposition of cell wall components and can fine-tune organ growth and sensitivity to soil pathogens. Cytokinin and auxin are two major hormonal regulators of plant growth. Here the authors identify SYAC1, a gene that is synergistically activated by the two hormones being applied together, and show that it is required for normal growth while negatively impacting pathogen resistance

Functional analysis of genes involved in ABA signaling and stress response in Arabidopsis thaliana seeds

L'acide abscissique (ABA) joue un rôle essentiel pour limiter la perte d'eau des plantes, grâce au contrôle du fonctionnement stomatique, et induire une large gamme de réponses de déficit hydrique. Au cours du développement de la graine, l'ABA induit la dormance et la tolérance à la dessiccation. Il intervient aussi dans le contrôle de la germination, notamment en réponse aux contraintes environnementales. Pour identifier de nouveaux acteurs du contrôle hormonal de la germination et de la réponse aux stimuli environnementaux, deux approches ont été utilisées. La première a consisté en l’identification de deux gènes dont les mutants sont affectés dans le contrôle hormonal de la germination et aussi, pour l’un d’entre eux, dans la tolérance au stress hydrique. Nous avons utilisé les techniques de séquençage profond pour identifier les gènes mutés. Le premier mutant, nommé xyl1-4, isolé pour sa tolérance à un inhibiteur de synthèse des gibbérellines, a permis de déterminer l’implication des xyloglucanes (XyG) dans le contrôle de la germination. En effet le locus XYL1 code pour une α-xylosidase pariétale impliquée dans la maturation des XyG, par clivage de résidus xylose qui composent leurs ramifications oligosaccharidiques. Nos résultats indiquent que XYL1 joue un rôle majeur dans les processus de remodelage de la paroi, qui contrôlent le potentiel de croissance de l’embryon et la résistance de l’albumen lors de la germination. Le second mutant, has2, a été sélectionné lors de la recherche de mutants suppresseurs des phénotypes d’évapotranspiration excessive du mutant de biosynthèse de l’ABA, aba3‐1 (Plessis et al., 2011). Il présente de nombreux phénotypes de sensibilité aux contraintes environnementales lors de la germination, impliquant des défauts de signalisation hormonale. Le locus HAS2 code une protéine mitochondriale à motifs PPR (pentatrico‐peptide repeat), déjà décrite sous les noms de LOI1/MEF11. L’analyse de ce mutant a permis ici de montrer l’importance de la respiration mitochondriale dans la tolérance à divers stress et le bon déroulement de la germination. Enfin, nous avons développé une démarche de génétique inverse pour analyser le rôle de trois protéines sHSP (small heat shock protein) mitochondriales dans la réponse aux stress abiotiques, en étudiant les défauts de germination des mutants simples et multiples des gènes HSP23.5, HSP23.6 et HSP26.5. Cette étude a mis en évidence le rôle majeur de HSP23.6 dans la réponse au stress salin et l’implication de ces trois protéines dans le contrôle de l’évaporation foliaire en réponse au déficit hydrique.Abscisic acid plays an essential role in limiting water loss from plants through the control of stomata aperture and the induction of a range of responses to water-‐‐deficit. During seed development ABA induces dormancy and desiccation tolerance as well as controlling germination, in particular in response to environmental constraints. Two approaches have been used to identify new factors involved in the hormonal control of germination and responses to environmental stimuli. The first consists of the identification of two genes defective in mutants affected in the hormonal control of germination, as well as water-deficit resistance in one mutant. Whole‐genome resequencing was used to identify the mutated genes. The first mutant, named xyl1-4, was isolated by its resistance to an inhibitor of gibberellin synthesis, and demonstrated the implication of xyloglucans (XyG) in germination control. In effect, the XYL1 locus encodes an α-xylosidase required for the maturation of XyG in the cell wall, through the trimming of xylose ramifications. Our results indicate that XYL1 plays a major role in the cell wall remodelling processes that control both embryo growth potential and the resistance of the endosperm during germination. The second mutant, has2, was selected in a screen for suppressor mutants of the excessive evapotranspiration on water deficit observed in the ABA biosynthesis mutant aba3-‐‐1 (Plessis et al., 2011). This mutant exhibits a range of germination phenotypes related to its sensitivity to environmental constraints, indicative of defects in hormone signalling. The HAS2 locus encodes a mitochondrial protein with PPR (pentatrico-peptide repeat) motifs that has previously been termed LOI1/MEF11. has2 mutant analysis showed the importance of mitochondrial respiration in plant tolerance to diverse stress and in germination processes. Finally we used a reverse genetic approach for the analysis of three mitochondrial sHSPs (small heat shock protein) in the response to abiotic stress; the germination phenotypes of single and multiple mutants for the HSP23.5, HSP23.6 and HSP26.5 genes were examined. This study has demonstrated the key role of HSP23.6 in the response to salt stress and the role of all three sHSPs in the control of evapotranspiration during water deficit

Etude microbiologique de l'influence de la craie sur la vase des etangs

National audienc

Action du carbonate de calcium sur la vase d'un etang. II. Effets d'un epandage en melange avec la vase

National audienc

Influence d'un stress de manipulation sur le transit de la microflore bacterienne digestive chez la truite arc-en-ciel Salmo gairdneri Richardson

National audienc

Emerging functions for cell wall polysaccharides accumulated during eudicot seed development

The formation of seeds is a reproductive strategy in higher plants that enables the dispersal of offspring through time and space. Eudicot seeds comprise three main components, the embryo, the endosperm and the seed coat, where the coordinated development of each is important for the correct formation of the mature seed. In addition, the seed coat protects the quiescent progeny and can provide transport mechanisms. A key underlying process in the production of seed tissues is the formation of an extracellular matrix termed the cell wall, which is well known for its essential function in cytokinesis, directional growth and morphogenesis. The cell wall is composed of a macromolecular network of polymers where the major component is polysaccharides. The attributes of polysaccharides differ with their composition and charge, which enables dynamic remodeling of the mechanical and physical properties of the matrix by adjusting their production, modification or turnover. Accordingly, the importance of specific polysaccharides or modifications is increasingly being associated with specialized functions within seed tissues, often through the spatio-temporal accumulation or remodeling of particular polymers. Here, we review the evolution and accumulation of polysaccharides during eudicot seed development, what is known of their impact on wall architecture and the diverse roles associated with these in different seed tissues