Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal. / Cette étude biosystématique a pour but de déterminer la composition, la nomenclature et l évolution de la section Conyzopsis. Les diverses hypothèses rapportées dans la documentation mentionnent la présence de deux, quatre ou cinq taxons reliés aux genres Aster, Erigeron, Conyza ou Brachyaçtis selon les auteurs consultés. Notre démarche expérimentale consiste à établir la morphologie, la distribution, l écologie, le nombre chromosomique, le mode de reproduction, la possibilité d'hybridation artificielle et les électrophorégrammes des taxons afin de connaître la distance génétique et les facteurs d'isolement entre les espèces. Nos travaux de recherche ont contribué largement à la connaissance de la biologie du groupe. Nos études taxonomiques traditionnelles nous ont permis d'établir la présence de trois taxons dans la section: Aster frondosus, A. brachyactis et A. Laurentianus. Ces trois espèces se caractérisent par des différenées morphologiques ténues mais nettes et des préférences écologiques distinctes. La culture de ces espèces dans des conditions uniformes, a confirmé la stabilité des caractères diagnostiques et révélé des différences dans le développement et la floraison de l'A. laurentianus. Cependant, les variétés de l A. laurentianus et les sous-espèces de l A. brachyactis ne sont pas reconnues. La cytologie nous a informés que la section Conyzopsis est composée d'espèces diploides à 2n = 14 chromosomes. L'étude de la reproduction nous a révélé que le groupe est autocompatible. L'A. brachyactis et l'A. laurentianus sont des espèces fortement autofécondes alors que l A. frondosus peut aussi se reproduire par fécondation croisée. Nos expériences d'hybridation artificielle ont démontré une interfécondité unididirectionnelle entre les espèces (A. brachyactis (♀) x A. frondosus (♂); A. laurentianus (♀) x A. frondosus (♂); A. laurentianus (♀) x A. brachyactis (♂)). Quoique des hybrides fertiles puissent être produits expérimentalement, l'isolement des espèces en nature est assuré par l'autofécondation de l A. brachyactis et de l'A. laurentianus. La production d'hybrides A. frondosus (♀) x A. modestus (♂) a confirmé les relations étroites du groupe étudie avec le genre Aster. Les analyses électrophorétiques ont mis en évidence une grande similarité génétique entre l'A. brachyactis et l'A. laurentianus et une distance plus considérable de l A. frondosus. L ensemble de nos résultats suggère une lignée évolutive caractérisée par deux spéciations rapides et successives: A. frondosus → A. brachyactis → A. laurentianus. La position ancestrale de l A. frondosus reflète une origine nord-américaine pour la section Conyzopsis.

The FRIABLE1 (FRB1) gene is identified to be a novel glycosyltransferase involved in cell adhesion, based on reverse genetics and immunocytochemistry studies. A total of 31 FRB1 paralogues were found in Arabidopsis thaliana using a bioinformatics approach. The following expression analysis has revealed 6 FRB1 paralogues to be pollen-specific. One pollen-specific FRB1 paralogue, At1g14970, exhibits longer silique lengths when exposed to higher than normal temperature at 28oC in its T-DNA insertional knockout when compared to Columbia wildtype plants. This may be due to the loss of temperature sensing and the continuous stimulated pollen tube cell wall growth or the up-regulation of genes that encode other glycosyltransferases. Thus, the identification of FRB1 paralogues and homologues in both rice and poplar may have tremendous potential to increase their yield in global warming for agricultural and industrial benefits.

The brevipedicellus (bp) mutant, caused by a loss-of-function mutation in the KNAT1 homeobox gene, is known to affect the stem morphogenesis. BP and ERECTA (ER) genes are required to promote internode and pedicel development and delineate nodal boundaries to maintain the radial symmetry of stems and pedicels. My research aims to identify genes acting on the BP pathway by utilizing a forward genetics approach. The suppressor4 mutant, identified from the bp er mutant screen, exhibits moderate length and perpendicularly-oriented pedicels with partially formed distal pedicel bulges, absent in the bp mutant. The kinky mutant, identified from the bp mutant screen, develops severe bends at the floral nodes and enhanced achlorophyllous stripes. These results suggest the SUPPRESSOR4 gene contribution in inhibiting the development of distal pedicel bulge and influencing both pedicel angle and length whereas the KINKY gene might act with BP in regulating proper inflorescence development.

In Arabidopsis, the F-box gene family encodes a large number of proteins postulated to act as substrate selectors for proteasome-mediated protein degradation. Recent reports document the importance of F-box proteins in developmental and metabolic signaling. Our microarray analyses of inflorescences of the brevipedicellus(bp) mutant indicate several F-box proteins are upregulated, suggesting that BP represses these genes in wild type plants to condition normal inflorescence development. We undertook analyses to examine the function of these proteins and their contribution to the pleiotropic phenotypes of bp. Yeast-2-hybrid screens revealed that the F-box protein At1g80440 binds to phenylalanine ammonia lyase-1(PAL1), the gateway enzyme of phenylpropanoid metabolism. Transgenic lines driven by the 35S cauliflower mosaic virus were attained but could not be propagated, suggesting a fatal phenotype. BP driven F-box expression results in phyllotaxy defects, manifest as alterations in the emergence of inflorescence and floral meristems in the axils of some cauline leaves.

Some Arabidopsis lesion mimic mutants (LMM) show alterations in abiotic stress responses as well as pathogen resistance. cpr22 is a LMM which has a mutation in cyclic nucleotide-gated ion channels, is a typical LMM exhibiting elevated levels of salicylic acid (SA), spontaneous cell death, constitutive expression of defense genes, and enhanced resistance to various pathogens in an SA dependant manner. cpr22 defense responses are suppressed in high humidity and enhanced by low humidity. To investigate environmental effects, microarray analyses were conducted. Expression of several genes related to abscisic acid (ABA) signaling was altered and ABA levels increased in cpr22 after humidity shift. Furthermore, significant alterations in ABA-related phenotypes were observed. Double mutant analysis with nahG plants indicated that alterations in ABA signaling were attributable to elevated SA levels. These results suggest a negative effect of SA on ABA signaling/abiotic stress responses during the activation of defense responses.

In Arabidopsis, the F-box gene family encodes a large number of proteins postulated to act as substrate selectors for proteasome-mediated protein degradation. Recent reports document the importance of F-box proteins in developmental and metabolic signaling. Our microarray analyses of inflorescences of the brevipedicellus(bp) mutant indicate several F-box proteins are upregulated, suggesting that BP represses these genes in wild type plants to condition normal inflorescence development. We undertook analyses to examine the function of these proteins and their contribution to the pleiotropic phenotypes of bp. Yeast-2-hybrid screens revealed that the F-box protein At1g80440 binds to phenylalanine ammonia lyase-1(PAL1), the gateway enzyme of phenylpropanoid metabolism. Transgenic lines driven by the 35S cauliflower mosaic virus were attained but could not be propagated, suggesting a fatal phenotype. BP driven F-box expression results in phyllotaxy defects, manifest as alterations in the emergence of inflorescence and floral meristems in the axils of some cauline leaves.

Some Arabidopsis lesion mimic mutants (LMM) show alterations in abiotic stress responses as well as pathogen resistance. cpr22 is a LMM which has a mutation in cyclic nucleotide-gated ion channels, is a typical LMM exhibiting elevated levels of salicylic acid (SA), spontaneous cell death, constitutive expression of defense genes, and enhanced resistance to various pathogens in an SA dependant manner. cpr22 defense responses are suppressed in high humidity and enhanced by low humidity. To investigate environmental effects, microarray analyses were conducted. Expression of several genes related to abscisic acid (ABA) signaling was altered and ABA levels increased in cpr22 after humidity shift. Furthermore, significant alterations in ABA-related phenotypes were observed. Double mutant analysis with nahG plants indicated that alterations in ABA signaling were attributable to elevated SA levels. These results suggest a negative effect of SA on ABA signaling/abiotic stress responses during the activation of defense responses.

Theory predicts that sexual reproduction confers an advantage over asexual reproduction due to the generation and maintenance of genetic variation afforded by the processes of recombination and segregation. However, this prediction has rarely been empirically tested. Oenothera is a flowering plant genus whose evolutionary history is punctuated with numerous transitions from sexual reproduction to a form of functionally asexual reproduction known as Permanent Translocation Heterozygosity (PTH). In Ch. 2, a greenhouse experiment examined patterns of phenotypic and genetic variation within and between populations across eight Oenothera species, representing four independent transitions to PTH. I found some evidence for a decrease in heritability and an increase in population differentiation in phenotypic traits associated with the loss of sex. Ch. 3 explored the possibility that rare outcrossing events represent a mechanism for the maintenance of variation in a PTH species. Analysis of microsatellite markers showed evidence for extremely low rates of outcrossing in natural populations (< 1%) of O. biennis, a PTH species.

Theory predicts that sexual reproduction confers an advantage over asexual reproduction due to the generation and maintenance of genetic variation afforded by the processes of recombination and segregation. However, this prediction has rarely been empirically tested. Oenothera is a flowering plant genus whose evolutionary history is punctuated with numerous transitions from sexual reproduction to a form of functionally asexual reproduction known as Permanent Translocation Heterozygosity (PTH). In Ch. 2, a greenhouse experiment examined patterns of phenotypic and genetic variation within and between populations across eight Oenothera species, representing four independent transitions to PTH. I found some evidence for a decrease in heritability and an increase in population differentiation in phenotypic traits associated with the loss of sex. Ch. 3 explored the possibility that rare outcrossing events represent a mechanism for the maintenance of variation in a PTH species. Analysis of microsatellite markers showed evidence for extremely low rates of outcrossing in natural populations (< 1%) of O. biennis, a PTH species.

As many as 70% of angiosperm species are known to contain polyploids, but many aspects of polyploid evolution are unclear in woody plants. Crataegus is a woody genus of Rosaceae comprising 140-200 species that are widely distributed in the Northern Hemisphere. Several species, particularly those in North America, are shown to contain polyploids. The overall goal of the thesis is to provide a better understanding of polyploid evolution by resolving problems from intergeneric to intraspecific levels in Crataegus using phylogenetic and population genetic approaches. Three major aspects were investigated: (1) Phylogeography of the Old and New World Crataegus; (2) Reproductive system and distribution of cytotypes of the black-fruited series Douglasianae in Pacific Northwest and; (3) Origins, population structure, and genetic diversity of diploid and polyploid species. Phylogenetic analyses of molecular data provide evidences of historical events such as trans-Beringian migrations and North Atlantic vicariance that contributed to modern distribution of Crataegus. Poor resolution and short internal branches in eastern North American species suggest genetic bottlenecks and/or rapid divergence following glaciations. In the Pacific Northwest, polyploids of series Douglasianae show a wider distribution and ecological amplitude than diploids. Parsimony tree and network analyses indicate that autotriploids and allotriploids occur in C. suksdorfii, while tetraploid C. suksdorfii are formed via the triploid bridge followed by introgression of sympatric C. douglasii. At the regional level, microsatellite data indicate a separation of the Pacific coastal diploids and triploids from the Columbia Plateau and Rocky Mountain triploids and tetraploids. High genetic differentiation among C. suksdorfii populations suggests that gene flow is limited by ploidy level differences as well as geographical distance. Within-population multilocus genotypic variation is greatest in sexual diploids, and least in apomictic triploids. Frequent gene flow via seed dispersal contributes to an appreciable level of intrapopulation diversity in apomictic tetraploids, and counterbalances the effects of apomixis and/or self-fertilization, which diminish genetic variation within and between seed families. These findings collectively clarify taxonomy and historical biogeography, provide an explicit reticulation model for polyploid formation, and shed light on evolution of natural populations in woody plants that show heterogeneous ploidy levels and reproductive systems.