Évolution des espaces fonctionnels dans la région administrative de Trois-Rivières

En effectuant en 1976 une enquête similaire à celle qui servit de base à la délimitation des régions et sous-régions administratives du Québec en 1965, on a défini, dans le cadre de la région administrative de Trois-Rivières, une hiérarchie des pôles d'attraction et délimité leurs zones d'influence. Les résultats comparés indiquent d'abord très peu de modifications au niveau de la hiérarchie, si ce n'est l'émergence de trois petites villes qui accèdent au palier inférieur de celle-ci. De même on remarque une relative stabilité dans la vie de relations entre les municipalités rurales et leurs pôles d'attraction urbains. Les mutations spatiales les plus importantes affectent la zone d'influence de la capitale régionale qui, favorisée par la mise en place en 1967 d'un lien routier permanent et gratuit avec la rive sud du Saint-Laurent, intensifie et étend son rayonnement dans ce secteur méridional de la région. Cette évolution des espaces fonctionnels trouve sa confirmation dans les options de regroupement prises par les municipalités lors de la formation des dix M.R.C. de la région l'an dernier.In 1976, while performing an investigation similar to the one which served as a basis for the identification of administrative regions and subregions of Québec in 1965, a hierarchy of attraction poles was defined and their spheres of influence identified, for the administrative region of Trois-Rivières.The resulting comparison indicated very little change in the hierarchy, except for the emergence of three smaller towns at the lower level of the hierarchical structure. One notices a relative stability in the links between the rural municipalities and their urban attraction pole. The most important spatial changes relate to the regional capital's zone of influence, which intensified and spread into the southern portion of the region, following the construction, in 1967, of a permanent and toll-free road link with the south shore of the St. Lawrence. The evolution of the region's spatial polarization is confirmed by the choices made last year at the municipal level during the merger process leading to the creation of the area's ten regional municipalities

De la Mauricie de Blanchard à la Mauricie actuelle : continuité et changements

Les auteurs examinent dans un premier temps comment la conception blanchardienne de la géographie s'incarne dans l'explication de cet espace régional et soulignent les difficultés de cette approche au plan de l'application. Cependant, grâce aux nombreux liens établis entre les divers éléments du tableau géographique, grâce également à la temporalité qui imprègne son oeuvre, Blanchard montre l'unité d'un espace que l'analyse paysagère avait eu tendance à diviser. Dans un deuxième temps, ils rendent compte des mutations qu'a connues la région depuis 1950 : effondrement des structures industrielles, déplacement du centre de gravité industriel vers le sud alors qu'en même temps, les agglomérations urbaines connaissaient une expansion spatiale soutenue malgré le ralentissement démographique. Enfin, l'espace rural mauricien a évolué vers une plus grande diversité des fonctions et son association à des degrés variables à l'espace forestier a fait place à un renforcement de son intégration au milieu urbain.This paper deals first with Blanchard's views on geography through his writings on La Mauricie region and underlines the difficulties of such an approach in its practical applications. However, through the numerous links which exist between the various elements of geographical description and also thanks to the time dimension in his writings, Blanchard shows the unity of this area which seemed to have been at first fragmented through landscape analysis. Second, the paper describes the changes the region has experienced since 1950: the collapse of the industrial structure the shift of the manufacturing centre of gravity to the south, while the urban agglomerations experienced continued spatial growth in spite of the lower rate of population growth. At last, the rural area of La Mauricie has evolved towards a greater functional diversification ; its varied links with the forest area have declined ; at the same time the rural areas have become increasingly integrated with the urban agglomerations

Gene family structure, expression and functional analysis of HD-Zip III genes in angiosperm and gymnosperm forest trees

BACKGROUND: Class III Homeodomain Leucine Zipper (HD-Zip III) proteins have been implicated in the regulation of cambium identity, as well as primary and secondary vascular differentiation and patterning in herbaceous plants. They have been proposed to regulate wood formation but relatively little evidence is available to validate such a role. We characterised and compared HD-Zip III gene family in an angiosperm tree, Populus spp. (poplar), and the gymnosperm Picea glauca (white spruce), representing two highly evolutionarily divergent groups. RESULTS: Full-length cDNA sequences were isolated from poplar and white spruce. Phylogenetic reconstruction indicated that some of the gymnosperm sequences were derived from lineages that diverged earlier than angiosperm sequences, and seem to have been lost in angiosperm lineages. Transcript accumulation profiles were assessed by RT-qPCR on tissue panels from both species and in poplar trees in response to an inhibitor of polar auxin transport. The overall transcript profiles HD-Zip III complexes in white spruce and poplar exhibited substantial differences, reflecting their evolutionary history. Furthermore, two poplar sequences homologous to HD-Zip III genes involved in xylem development in Arabidopsis and Zinnia were over-expressed in poplar plants. PtaHB1 over-expression produced noticeable effects on petiole and primary shoot fibre development, suggesting that PtaHB1 is involved in primary xylem development. We also obtained evidence indicating that expression of PtaHB1 affected the transcriptome by altering the accumulation of 48 distinct transcripts, many of which are predicted to be involved in growth and cell wall synthesis. Most of them were down-regulated, as was the case for several of the poplar HD-Zip III sequences. No visible physiological effect of over-expression was observed on PtaHB7 transgenic trees, suggesting that PtaHB1 and PtaHB7 likely have distinct roles in tree development, which is in agreement with the functions that have been assigned to close homologs in herbaceous plants. CONCLUSIONS: This study provides an overview of HD-zip III genes related to woody plant development and identifies sequences putatively involved in secondary vascular growth in angiosperms and in gymnosperms. These gene sequences are candidate regulators of wood formation and could be a source of molecular markers for tree breeding related to wood properties

Apoplast proteome reveals that extracellular matrix contributes to multistress response in poplar

<p>Abstract</p> <p>Background</p> <p>Riverine ecosystems, highly sensitive to climate change and human activities, are characterized by rapid environmental change to fluctuating water levels and siltation, causing stress on their biological components. We have little understanding of mechanisms by which riverine plant species have developed adaptive strategies to cope with stress in dynamic environments while maintaining growth and development.</p> <p>Results</p> <p>We report that poplar (<it>Populus </it>spp.) has evolved a systems level "stress proteome" in the leaf-stem-root apoplast continuum to counter biotic and abiotic factors. To obtain apoplast proteins from <it>P. deltoides</it>, we developed pressure-chamber and water-displacement methods for leaves and stems, respectively. Analyses of 303 proteins and corresponding transcripts coupled with controlled experiments and bioinformatics demonstrate that poplar depends on constitutive and inducible factors to deal with water, pathogen, and oxidative stress. However, each apoplast possessed a unique set of proteins, indicating that response to stress is partly compartmentalized. Apoplast proteins that are involved in glycolysis, fermentation, and catabolism of sucrose and starch appear to enable poplar to grow normally under water stress. Pathogenesis-related proteins mediating water and pathogen stress in apoplast were particularly abundant and effective in suppressing growth of the most prevalent poplar pathogen <it>Melampsora</it>. Unexpectedly, we found diverse peroxidases that appear to be involved in stress-induced cell wall modification in apoplast, particularly during the growing season. Poplar developed a robust antioxidative system to buffer oxidation in stem apoplast.</p> <p>Conclusion</p> <p>These findings suggest that multistress response in the apoplast constitutes an important adaptive trait for poplar to inhabit dynamic environments and is also a potential mechanism in other riverine plant species.</p

Functional Analysis of the PgCesA3 White Spruce Cellulose Synthase Gene Promoter in Secondary Xylem

Cellulose is an essential structural component of the plant cell wall. Its biosynthesis involves genes encoding cellulose synthase enzymes and a complex transcriptional regulatory network. Three cellulose synthases have been identified in conifers as being potentially involved in secondary cell wall biosynthesis because of their preferential expression in xylem tissues; however, no direct functional association has been made to date. In the present work, we characterized the white spruce [Picea glauca (Moench) Voss] cellulose synthase PgCesA3 gene and 5′ regulatory elements. Phylogenetic analysis showed that PgCesA1-3 genes grouped with secondary cell wall-associated Arabidopsis cellulose synthase genes, such as AtCesA8, AtCesA4, and AtCesA7. We produced transgenic spruce expressing the GUS reporter gene driven by the PgCesA3 promoter. We observed blue staining in differentiating xylem cells from stem and roots, and in foliar guard cells indicating that PgCesA3 is clearly involved in secondary cell wall biosynthesis. The promoter region sequence of PgCesA3 contained several putative MYB cis-regulatory elements including AC-I like motifs and secondary wall MYB-responsive element (SMRE); however, it lacked SMRE4, 7 and 8 that correspond to the sequences of AC-I, II, and III. Based on these findings and results of previous transient trans-activation assays that identified interactions between the PgCesA3 promoter and different MYB transcription factors, we performed electrophoretic mobility shift assays with MYB recombinant proteins and cis-regulatory elements present in the PgCesA3 promoter. We found that PgMYB12 bound to a canonical AC-I element identified in the Pinus taeda PAL promoter and two AC-I like elements. We hypothesized that the PgMYB12 could regulate PgCesA3 in roots based on previous expression results. This functional study of PgCesA3 sequences and promoter opens the door for future studies on the interaction between PgMYBs and the PgCesA3 regulatory elements

Infection assays in Arabidopsis reveal candidate effectors from the poplar rust fungus that promote susceptibility to bacteria and oomycete pathogens

Fungi of the Pucciniales order cause rust diseases which, altogether, affect thousands of plant species worldwide and pose a major threat to several crops. How rust effectors—virulence proteins delivered into infected tissues to modulate host functions— contribute to pathogen virulence remains poorly understood. Melampsora larici-populina is a devastating and widespread rust pathogen of poplar, and its genome encodes 1184 identified small secreted proteins that could potentially act as effectors. Here, following specific criteria, we selected 16 candidate effector proteins and characterized their virulence activities and subcellular localizations in the leaf cells of Arabidopsis thaliana. Infection assays using bacterial (Pseudomonas syringae) and oomycete (Hyaloperonospora arabidopsidis) pathogens revealed subsets of candidate effectors that enhanced or decreased pathogen leaf colonization. Confocal imaging of green fluorescent protein-tagged candidate effectors constitutively expressed in stable transgenic plants revealed that some protein fusions specifically accumulate in nuclei, chloroplasts, plasmodesmata and punctate cytosolic structures. Altogether, our analysis suggests that rust fungal candidate effectors target distinct cellular components in host cells to promote parasitic growth. © 2016 BSPP AND JOHN WILEY & SONS LTD

The expression pattern of the Picea glauca Defensin 1 promoter is maintained in Arabidopsis thaliana, indicating the conservation of signalling pathways between angiosperms and gymnosperms*

A 1149 bp genomic fragment corresponding to the 5' non-coding region of the PgD1 (Picea glauca Defensin 1) gene was cloned, characterized, and compared with all Arabidopsis thaliana defensin promoters. The cloned fragment was found to contain several motifs specific to defence or hormonal response, including a motif involved in the methyl jasmonate reponse, a fungal elicitor responsive element, and TC-rich repeat cis-acting element involved in defence and stress responsiveness. A functional analysis of the PgD1 promoter was performed using the uidA (GUS) reporter system in stably transformed Arabidopsis and white spruce plants. The PgD1 promoter was responsive to jasmonic acid (JA), to infection by fungus and to wounding. In transgenic spruce embryos, GUS staining was clearly restricted to the shoot apical meristem. In Arabidopsis, faint GUS coloration was observed in leaves and flowers and a strong blue colour was observed in guard cells and trichomes. Transgenic Arabidopsis plants expressing the PgD1::GUS construct were also infiltrated with the hemibiotrophic pathogen Pseudomonas syringae pv. tomato DC3000. It caused a suppression of defensin expression probably resulting from the antagonistic relationship between the pathogen-stimulated salicylic acid pathway and the jasmonic acid pathway. It is therefore concluded that the PgD1 promoter fragment cloned appears to contain most if not all the elements for proper PgD1 expression and that these elements are also recognized in Arabidopsis despite the phylogenetic and evolutionary differences that separates them