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International audience; In hardwood trees, tension wood formation is a remarkable adaptive mechanism that makes possible for the tree to reorient its axis. Tension wood differs from normal wood by anatomical, chemical and physical characteristics: it is less lignified, and contains more cellulose of higher crystallinity, with longitudinally oriented microfibrils. In poplar, tension wood fibers harbor an extra cell wall layer, named G-layer, responsible for the peculiar mechanical properties of tension wood (1). We propose that differences between tension and normal wood mechanical properties are linked to the polysaccharide composition of the G-layer. In order to investigate the nature of these links, we realized immunolocalisation studies with light microscope observation. 158 monoclonal antibodies (from CCRC, LM, JIM and MAC series) raised against various epitopes specific to different families of plant cell wall polysaccharides were tested. For each antibody tested, we analyzed where labeling was present, not only between tension and opposite wood (that is completely devoid of G-fibres), but also according to cell type, cell wall layer, and this along the gradient of xylem cell differentiation. Most antibodies directed against xyloglucans, fucosylated or not, specifically labeled the primary wall / middle lamella in both tension and opposite wood fibers. This was also the case for several antibodies specific to rhamnogalacturonans I. Some other antibodies labeled only the S2 layer, such as most antibodies directed against xylans, whereas, unexpectedly, a few other xylan-specific antibodies exhibited a wider range of labeling. None of the antibody tested was able to specifically label opposite wood cell walls. On the contrary, among all the antibodies directed against rhamnogalacturonan I or arabinogalactan epitopes that were tested, eighteen of them specifically labeled the G-layer in tension wood fibers and, for some of them, the labeling was restricted to newly formed G-layers. Overall, from the signals obtained with each of the antibody tested, differences between tension and opposite wood fibers when observed were only detected at the level of the G-layer whose composition appears to evolve throughout its maturation. Furthermore, our study strongly suggests the involvement of specific arabinogalactan-proteins and pectins during G-layer construction. Finally, we optimized a procedure for G-layer isolation in order to analyze the polysaccharide composition of purified G-layers by mass spectrometry. In the presentation, we will discuss more in details all the results obtained using these two complementary approaches.

Demande Internationale PCT n° PCT/IB2010/052590; The invention relates to the production of plants having a reduced lignin content and in which the cellulose hydrolysis of the walls is increased, via the total or partial inhibition of the expression and/or the activity of two laccases in said plant.

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.

https://www.worldcat.org/title/sustainable-forestry-wood-products-and-biotechnology-proceedings-of-an-international-conference-held-november-11-14-2002-vitoria-gasteiz-spain/oclc/704189088&referer=brief_results; International audience; A controlled cross between two Douglas-fir trees, from Washington State, have been analysed for genetic mapping and for QTL detection. Their progeny have been measured for stem height, bud flushing, and polycyclism on the second and third year after sawing. A genetic map was drawn from segregations of AFLP markers recorded in 157 seedlings. These markers were obtained with 25 primer pairs tested in other Pinaceae species. Genetic map of the female parent consisted of 123 markers distributed in 24 linkage groups. QTLs have been detected by interval mapping for traits showing a normal distribution (stem height, stem elongation), and by a Kruskal and Wallis test for trait that did not show a normal distribution (bud flushing, polycyclism). QTLs have been detected for all investigated traits. QTLs for growth and flushing traits did not overlapped on the female genetic map. QTLs for vegetative flushing stage of terminal bud recorded in 2001 and for day of bud elongation recorded in 2002 did not overlapped. Further evaluations of quantitative traits are required to test time stability of QTLs.

This work is part of an ANR - Genoplante 2010 research project entitled: “Molecular bases of acclimation and adaptation to water deficit in poplar” (POPSEC, 2007-2009).; International audience; The numerous molecular studies on drought response in plants were mostly focused on short-term responses without considering dose-response effects. Moreover, despite the importance of xylem in tree water relations, assessments of drought-induced gene expression in wood are very scarce. In this work, we investigated xylem correlations between histological characteristics induced by water shortage and drought-induced gene expression. The experimental plan consisted of two Populus deltoides x Populus nigra hybrid clones (Soligo and Carpaccio) contrasted for their tolerance to water shortage and four water regimes: one short-term response to water deficit and two long-term responses either to mild and moderate water deficit and the well-watered control. For each condition tested, six trees were dedicated to molecular studies and three for ecophysiological and growth measurements. After histological staining of stem cross sections, image analysis was carried out on selected areas corresponding to stressed xylem. Total vessel lumen area was consistently higher in Carpaccio as compared to Soligo, whatever the stress condition. Interestingly, under the most stringent water shortage, Soligo exhibited a significant increase of the cell wall/ray cell fraction and an increase of water use efficiency. Spatial statistics are underway to better describe the variability of these histological variables. In addition, complete debarked stem samples and cambial zones only plus very young differentiating scraped xylem were analyzed on whole-genome Affymetrix poplar arrays. We identified modules of co-expressed genes especially using a new clustering algorithm developed by Maere et al. (BMC Systems Biology 2008, 2:33). A limited number of modules are representative of clone-specific responses but some others are potentially correlated to genotype-treatment interactions. Prospective models to integrate these phenotypic, ecophysiological and gene expression data will be discussed.

National audience

International audience; Comparative QTL mapping for adaptive traits among populations and species can lead to the identification of genomic regions conserved over a long evolutionary period and therefore potentially harboring genes of great importance for adaptive processes. At the same time, non-conserved QTLs could be responsible for local adaptation or interspecific differentiation. The availability of Populus as a model system for tree and woody perennial plant biology has largely been driven by the rapid development of genomic and molecular biology resources for this genus, culminating in the completion of a draft sequence of the Populus trichocarpa (black cottonwood) genome. Numerous genetic maps are available in different Populus and Salix species and QTLs for adaptive traits (such as phenology and disease resistance) and sex have been mapped. All these maps showed a very good synteny with the P. trichocarpa genome; however, very few markers are currently shared between these maps. The objective of our study is to take advantage of the information on the P. trichocarpa genome sequence to perform QTL projection and identify candidate genes. Genetic maps from 7 pedigrees, belonging to 4 Populus spp. were aligned with the help of common simple sequence repeat and gene markers. Three additional published maps from Salix spp. were partially anchored to the P. trichocarpa genome sequence. QTL meta-analysis and projection of QTL intervals on the genome sequence were performed when sufficient genome anchoring markers were available. These analyses allowed identifying large genome regions containing several hundred of candidate genes. Thanks to the availability of biological knowledge accumulated in public data bases (e.g. Gene Ontology) and high-throughput enrichment tools, we have explored these gene lists by functional analysis if QTL regions are statistically enriched in some functional categories compared to the entire genome.

Among the ecosystem services provided by forests, wood provisioning takes a central position. Wood and derived products have played a critical role in the evolution of human kind and demand for raw material is increasing in a foreseeable future. Wood is used for energy production, construction and a wide variety of products for which different properties are required. Anatomical, chemical and physical properties of wood are determined through a complex process called xylogenesis controlled by internal and external signals and occurring during the life of the tree. In this chapter we describe i/how wood is formed and ii/the different factors controlling this developmental process with emphasis on the molecular machinery involved, iii/the functions of wood and iv/the biotechnology approaches developed to improve wood biomass production and properties genetically.