The genus Populus consists of many ecologically and economically important forest tree species. Their rapid growth makes them one of the most productive hardwoods growing in temperate latitudes. Populus spp. frequently hybridize where their ranges overlap, and poplar hybrids are the most frequently planted genotypes for fiber production. To better understand the genomics of hybridization in Populus, we sampled and sequenced the genome of 574 poplar trees from six east-west transects across the hybrid zone between Populus trichocarpa and Populus balsamifera in western North America. I used these data to characterize population structure within and between transects, and hybridization between the species. There was a consistent transition from greater P. balsamifera ancestry in the north and east to greater P. trichocarpa ancestry in the south and west. Hybridization between the species was common across each of the six transects, though more common in colder climates. The results also showed that both latitude and longitude affect the genetic structure of this species complex, and that subtle introgression from P. balsamifera may facilitate adaptation of P. trichocarpa to colder climates. / Master of Science / The genus Populus has many ecologically and economically important forest tree species. Balsam poplar (Populus balsamifera) and black cottonwood (Populus trichocarpa) are two such species, both for fiber production and models for understanding tree biology and adaptation. Whereas black cottonwood is distributed close to the west coast of North America from California through Alaska, balsam poplar mostly occurs across the interior of Canada from Newfoundland through Alberta. Where their ranges overlap, the species often hybridize. In this study, we used genome sequencing of trees collected across six east-west transects from Washington state through British Columbia, Canada, and Alaska to understand genetic variation and the geography of hybridization. I found evidence of widespread hybridization across all transects. While the influence of P. balsamifera was extensive in northern populations, a large number of pure P. trichocarpa were found in southern populations. The transition from P. trichocarpa to P. balsamifera was also steeper in the south than the north, with a narrower hybrid zone in the south. Additionally, I found that gene flow among some populations was limited by temperature and geographical barriers. Taken together, my results suggest genetic structure and hybridization within and between these species is driven by climate variation, and that P. balsamifera ancestry may help northern P. trichocarpa populations adapt to their local environments.

No description available.

As drought can impinge significantly on forest health and productivity, the mechanisms by which forest trees respond to drought is of interest. The research presented herein examined the intra-specific variation in the Populus balsamifera drought response, examining the potential role of the transcriptome to configure growth, metabolism and development in response to water deficit. Amassing evidence indicates that different species of Populus have divergent mechanisms and Three lines of inquiry were pursued to investigate the intraspecific variation the drought response in P. balsamifera. First, the transcriptome responses of six genotypes of P. balsamifera were examined using Affymetrix Poplar GeneChips under well-watered and water-deficit conditions. A core species-level transcriptome response was identified. Significantly, intraspecific variation in the drought transcriptome was also identified. The data support a role for genotype-derived variation in the magnitude of P. balsamifera transcriptome remodelling playing a role in conditioning drought responsiveness. Second, the impact of drought-stress induced declines in stomatal conductance, as well as an alteration in stomatal development in two genotypes was examined. Patterns of transcript abundance of genes hypothesised to underpin stomatal development had patterns congruent with their role in modulation of stomatal development. These results suggest that stomatal development may play a role as a long-term mechanism to limit water loss from P. balsamifera leaves under conditions of drought-stress. Finally, the drought-induced metabolome of six P. balsmaifera genotypes was interrogated. Metabolite profiling reveled amino acids such as isoleucine and proline and sugars such as galactinol and raffinose were found with increased abundance, whereas TCA intermediates succinic and malic acid were found with decreased abundance in response to drought. Comparative analysis of the metabolome and the transcriptome revealed genotypic-specific variation in energy and carbohydrate metabolism. Taken together, the findings reported in this thesis form a foundation to understand the basis of intraspecific variation in the drought response in P. balsamifera. Transcripts and metabolites that contribute to within-species differences in drought tolerance were defined. These molecular components are useful targets for both future study, as well as efforts aimed at protecting and growing trees of this important species under challenging environmental conditions.

As drought can impinge significantly on forest health and productivity, the mechanisms by which forest trees respond to drought is of interest. The research presented herein examined the intra-specific variation in the Populus balsamifera drought response, examining the potential role of the transcriptome to configure growth, metabolism and development in response to water deficit. Amassing evidence indicates that different species of Populus have divergent mechanisms and Three lines of inquiry were pursued to investigate the intraspecific variation the drought response in P. balsamifera. First, the transcriptome responses of six genotypes of P. balsamifera were examined using Affymetrix Poplar GeneChips under well-watered and water-deficit conditions. A core species-level transcriptome response was identified. Significantly, intraspecific variation in the drought transcriptome was also identified. The data support a role for genotype-derived variation in the magnitude of P. balsamifera transcriptome remodelling playing a role in conditioning drought responsiveness. Second, the impact of drought-stress induced declines in stomatal conductance, as well as an alteration in stomatal development in two genotypes was examined. Patterns of transcript abundance of genes hypothesised to underpin stomatal development had patterns congruent with their role in modulation of stomatal development. These results suggest that stomatal development may play a role as a long-term mechanism to limit water loss from P. balsamifera leaves under conditions of drought-stress. Finally, the drought-induced metabolome of six P. balsmaifera genotypes was interrogated. Metabolite profiling reveled amino acids such as isoleucine and proline and sugars such as galactinol and raffinose were found with increased abundance, whereas TCA intermediates succinic and malic acid were found with decreased abundance in response to drought. Comparative analysis of the metabolome and the transcriptome revealed genotypic-specific variation in energy and carbohydrate metabolism. Taken together, the findings reported in this thesis form a foundation to understand the basis of intraspecific variation in the drought response in P. balsamifera. Transcripts and metabolites that contribute to within-species differences in drought tolerance were defined. These molecular components are useful targets for both future study, as well as efforts aimed at protecting and growing trees of this important species under challenging environmental conditions.

The composition of lignin in the outer cell-wall layers of spruce and poplar has been studied and the data obtained have been compared with those of the mature reference wood in which the secondary cell wall predominates. Materials with exclusively or predominantly outer cell-wall layers were examined. Accurate data relating to the lignin monomer composition and the number of β-O-4´ bonds were obtained from pure middle lamella/primary cell wall lignin. Firstly, a 10 000 year old white spruce material, with most of the secondary cell wall missing, was studied. The aged lignin was composed of guaiacyl units only, and was slightly more condensed but otherwise similar to the reference lignin. Secondly, the developing xylem of a Norway spruce clone was analyzed during a growth season. In spring and early summer, growth is very rapid and the intention was to sample tissues in which the secondary cell-wall layers had not yet lignified, but where the outer layers at least had started to lignify. Microscopy, Klason lignin and carbohydrate analyses showed that the lignin in the developing xylem of samples from mid-June was located exclusively in the middle lamella. The lignin was more condensed, was composed of guaiacyl units only and contained more end-groups than the reference Norway spruce wood. Thirdly, the cambial tissues of a Balsam poplar clone were surveyed during a growth season. Both the phloem side and the xylem side of the cambial region were examined. The Klason lignin content and carbohydrate monomer distribution showed that in June and August the tissues on the phloem side contained material with mainly middle lamella/primary walls. In June, the xylem side in the cambial region contained mainly middle lamella/primary walls, and in August the secondary cell wall carbohydrates were being deposited. Both tissues contained lignin that was more condensed and had more end-groups than the reference lignin. In mid-June, the developing xylem had a ratio of syringyl to guaiacyl units of 0.6, whereas the ratio for the reference wood was 1.3. In the final study, lignin from the primary cell walls from a hybrid aspen cell suspension culture was investigated. The lignin contained only guaiacyl units which were more condensed than those observed in the reference poplar wood. / <p>QC 20100920</p>

La prévalence de l’obésité, du diabète de type 2, et du syndrome métabolique, sont à la hausse chez les Cris d’Eeyou Istchee (CEI-Nord du Québec). Ces problèmes sont aggravés par leur diète non traditionnelle, leur sédentarité, ainsi que par une résistance culturelle aux produits pharmaceutiques. Afin de développer des traitements antidiabétiques culturellement adaptés, notre équipe a effectué une enquête ethnobotanique qui a identifié 17 plantes provenant de la pharmacopée traditionnelle des CEI. À partir des études de criblage effectuées in vitro, deux plantes parmi les 17 ont attiré notre attention. Populus balsamifera L. (Salicaceae) pour ses propriétés anti-obésité et Larix laricina K. Koch (Pinaceae) pour ses propriétés antidiabétiques. P. balsamifera et son composé actif salicortin ont inhibé l’accumulation de triglycérides durant l’adipogénèse dans les adipocytes 3T3-L1. L. laricina a augmenté le transport de glucose et l’activation de l’AMPK dans les cellules musculaires C2C12, l’adipogénèse dans les 3T3-L1 et a démontré un fort potentiel découpleur (propriété anti-obésité). Les objectifs de cette thèse sont d'évaluer les potentiels anti-obésité et antidiabétique et d’élucider les mécanismes d'action de P. balsamifera, salicortin, et L. laricina chez la souris C57BL/6 rendue obèse par une diète riche en gras (HFD). Les souris ont été soumises pendant huit (étude préventive) ou seize semaines (étude traitement) à une HFD, ou à une HFD dans laquelle P. balsamifera, salicortin, ou L. laricina a été incorporé soit dès le départ (prévention), ou dans les 8 dernières des 16 semaines d'administration de HFD (traitement). iv Les résultats démontrent que P. balsamifera (dans les deux études) et salicortin (évalué dans l’étude traitement) diminuent: le poids corporel, le gras rétropéritonéal, la sévérité de la stéatose et l’accumulation de triglycérides hépatique (ERK impliqué), les niveaux de glycémie et d'insuline, et le ratio leptine/adiponectine. Dans les deux études, P. balsamifera a significativement réduit la consommation de nourriture mais cet effet coupe-faim nécessite d’être approfondi. Dans l'étude préventive, P. balsamifera a augmenté la dépense énergétique (hausse de la température à la surface de la peau et de l’activation de la protéine découplante-1; UCP-1). Les voies de signalisation activées par P. balsamifera et par salicortin (de façon plus modeste) sont impliquées dans: la production de glucose hépatique (Akt), l’expression de Glut4 dans le muscle squelettique, la captation du glucose et du métabolisme des lipides (Akt dans le tissu adipeux), la différenciation des adipocytes (ERK et PPARg), l’inflammation dans le foie (IKKαβ), et l'oxydation des acides gras dans le muscle, le foie, ou le tissu adipeux (PPARa et CPT-1). D’autre part, L. laricina a également diminué les niveaux de glycémie et d’insuline, le ratio leptine/adiponectine, le gras rétropéritonéal et le poids corporel. Ces effets ont été observés en conjonction avec une augmentation de la dépense énergétique: hausse de température à la surface de la peau (prévention) et amélioration de la fonction mitochondriale et de la synthèse d'ATP (traitement). En conclusion, l’utilisation de P. balsamifera, salicortin et L. laricina comme des traitements alternatifs et culturellement adaptés aux CEI représente une contribution importante dans la prévention et le traitement de l’obésité et du diabète. / The prevalence of obesity, insulin resistance, and the metabolic syndrome is increasing among the Cree of Eeyou Istchee (CEI - Northern Quebec). Non-traditional diet and sedentary lifestyle along with cultural disconnect of modern type 2 diabetes (T2D) therapies are involved. In order to establish culturally adapted antidiabetic treatments, our research team conducted an ethnobotanical survey, where 17 plants were identified from the CEI traditional pharmacopoeia. Based on data obtained from in vitro screening studies, two plant species out of 17 were of particular interest for their properties as antiobesity, namely Populus balsamifera L. (Salicaceae), and antidiabetic agents, namely Larix laricina K. Koch (Pinaceae). P. balsamifera and its active salicortin inhibited triglyceride accumulation during adipogenesis in 3T3-L1 adipocytes. L. laricina increased glucose uptake and AMPK activation in C2C12 myotubes, adipogenesis in the 3T3-L1 adipocyte cell line, and was observed as one of the strongest uncouplers, severely disrupting mitochondrial function (increasing fuel consumption/metabolic rate; antiobesity property). The purpose of this PhD thesis is to evaluate the antiobesity and antidiabetic potential of P. balsamifera, salicortin, and L. laricina, in an in vivo model of diet-induced obese (DIO) C57BL/6 mice, as well as to investigate their possible mechanisms of action. Mice were subjected for eight (prevention study) or sixteen weeks (treatment study) to a high fat diet (HFD), or HFD to which P. balsamifera, salicortin, or L. laricina were incorporated either at onset (prevention), or in the last 8 of the 16 weeks of administration of the HFD (treatment). The results showed that P. balsamifera (in either study) and salicortin (incorporated in HFD only in treatment study) decreased the weight of whole vii body, retroperitoneal fat pad, reduced the severity of hepatic macrovesicular steatosis and triglyceride accumulation (ERK pathway implicated). They also decreased glycemia and improved insulin sensitivity by diminishing insulin levels, and altering adipokine secretion whereby reducing the leptin/adiponectin ratio. In both studies, P. balsamifera significantly reduced food intake. This appetite-reducing effect needs to be investigated further. In the prevention study this was accompanied by an increase in energy expenditure (increase in skin temperature and tends to increase expression of uncoupling protein-1; UCP-1). The signaling pathways activated by P. balsamifera and slightly by salicortin are implicated in either controlling hepatic glucose output (Akt), skeletal muscle Glut4 expression, glucose uptake and lipid metabolism in adipose tissue (Akt), adipocyte differentiation (ERK pathway and PPARg), decreasing the hepatic inflammatory state (IKKab), and increasing muscular, hepatic, or adipose tissue fatty acid oxidation (PPARa, CPT-1). As for L. laricina, it effectively decreased glycemia levels, insulin levels and the leptin/adiponectin ratio, improved insulin sensitivity and slightly decreased abdominal fat pad and body weights. This occurred in conjunction with increased energy expenditure as demonstrated by elevated skin temperature in the prevention study, and tendency to improve mitochondrial function and ATP synthesis in the treatment protocol. In conclusion, these results represent a major contribution, identifying P. balsamifera, salicortin, and L. laricina, as promising alternative, and culturally adapted therapies for the prevention and treatment care of obesity and diabetes among the CEI.

No description available.