Plant-wide communication between tissues and cells is organized, in part, by a suite of compounds called hormones. I have chosen to focus on the effects of one plant hormone, ethylene; how its synthesis is controlled and how its perception is mediated to differentially control cell development and response to pathogens. In the production of ethylene, one level of control is by modulating the levels of the immediate precursor to ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC). I characterize here a plant encoded gene homologous to bacterial ACC Deaminases, AtACD1, and show through up- and down-regulation of the gene that it can modulate the plants sensitivity to exogenous ACC. Once ethylene is produced, it is sensed in Arabidopsis thaliana by a family of 5 receptors. I show that ETR2 in Arabidopsis is responsible for modulation of the microtubule cytoskeleton assembly as loss-of –function mutations to this gene cause randomized microtubule assembly in trichomes and increase sensitivity to microtubule depolymerising drugs in root hairs. In studies of plant:pathogen interactions, ethylene is a central signaling agent required for plant resistance. While it has been shown that etr1 mutants show increased susceptibility to fungal pathogens, exogenous ethylene has also been shown to speed the progress of pathogenesis. Using Fumonisin B1 (FB1) to induce cell death I show that etr1-1 has accelerated cell death while ein4-1 has a reduced rate of necrosis. Further to this, mutations to the other three ethylene receptors do not have any effect on the rate of cell death. My interest in cell development led to the characterization of an activation tagged Populus tremula x P. alba line with increased trichome initiation. The gene responsible for these phenotypes was identified as PtMYB186, which also affected growth rate, transpiration rate, photosynthetic capacity, and resistance to the Tussock moth larvae. Together these studies provide a new framework for our understanding of how the ethylene signal is modulated in plants and the controls behind cellular development. This knowledge will help reconcile studies which show that ethylene has different effects on plant development and provide new avenues of research into trichome development. / Thesis (Ph.D, Biology) -- Queen's University, 2009-01-13 10:08:03.605

Plants often live in association with growth-promoting bacteria, which provide them with several benefits. One such benefit is the lowering of plant ethylene levels through the action of the bacterial enzyme 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase that cleaves the immediate biosynthetic precursor of ethylene, ACC. The plant hormone ethylene is responsible for many aspects of plant growth and development but under stressful conditions ethylene exacerbates stress symptoms. The ACC deaminase-containing bacterium Pseudomonas putida UW4, isolated from the rhizosphere of reeds, is a potent plant growth-promoting strain and as such was used, along with an ACC deaminase minus mutant of this strain, to study the role of ACC deaminase in plant growth-promotion. Also, transgenic plants expressing a bacterial ACC deaminase gene were used to study the role of this enzyme in plant growth and stress tolerance in the presence and absence of nickel. Transcriptional changes occurring within plant tissues were investigated with the use of an Arabidopsis oligonucleotide microarray. The results showed that transcription of genes involved in hormone regulation, secondary metabolism and the stress response changed in all treatments. In particular, the presence of ACC deaminase caused genes for auxin response factors to be up-regulated in plant tissues suggesting a de-repression of auxin signaling in the absence of high levels of ethylene. Also, transgenic plants had longer roots and grew faster than the non-transformed plants and genes involved in the stress response and secondary metabolism were up-regulated. Plants inoculated with bacteria had lower levels of secondary metabolism gene expression and slightly higher stress response gene expression than uninoculated plants. Yet, inoculation with the ACC deaminase-expressing bacterium caused less up-regulation of plant genes involved in stress and defense responses and the down-regulation of genes involved in nitrogen metabolism in comparison to plants inoculated with the ACC deaminase minus mutant. Nickel stress caused the down-regulation of genes involved in photosynthesis and carbon fixation and the up-regulation of genes involved in stress responses, and amino acid and lipid breakdown suggesting energy starvation. When transgenic plants expressing ACC deaminase in the roots were exposed to nickel stress, plant stress symptoms were significantly lower and biomass was significantly higher suggesting that lowering the level of ethylene relieved many of the stress symptoms. In fact, genes involved in photosynthesis, secondary metabolism and nitrate assimilation were up-regulated in transgenic plants compared with non-transformed plants in the presence of nickel, suggesting that ACC deaminase is effective at reducing the severe effects of this metal stress.

Plants often live in association with growth-promoting bacteria, which provide them with several benefits. One such benefit is the lowering of plant ethylene levels through the action of the bacterial enzyme 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase that cleaves the immediate biosynthetic precursor of ethylene, ACC. The plant hormone ethylene is responsible for many aspects of plant growth and development but under stressful conditions ethylene exacerbates stress symptoms. The ACC deaminase-containing bacterium Pseudomonas putida UW4, isolated from the rhizosphere of reeds, is a potent plant growth-promoting strain and as such was used, along with an ACC deaminase minus mutant of this strain, to study the role of ACC deaminase in plant growth-promotion. Also, transgenic plants expressing a bacterial ACC deaminase gene were used to study the role of this enzyme in plant growth and stress tolerance in the presence and absence of nickel. Transcriptional changes occurring within plant tissues were investigated with the use of an Arabidopsis oligonucleotide microarray. The results showed that transcription of genes involved in hormone regulation, secondary metabolism and the stress response changed in all treatments. In particular, the presence of ACC deaminase caused genes for auxin response factors to be up-regulated in plant tissues suggesting a de-repression of auxin signaling in the absence of high levels of ethylene. Also, transgenic plants had longer roots and grew faster than the non-transformed plants and genes involved in the stress response and secondary metabolism were up-regulated. Plants inoculated with bacteria had lower levels of secondary metabolism gene expression and slightly higher stress response gene expression than uninoculated plants. Yet, inoculation with the ACC deaminase-expressing bacterium caused less up-regulation of plant genes involved in stress and defense responses and the down-regulation of genes involved in nitrogen metabolism in comparison to plants inoculated with the ACC deaminase minus mutant. Nickel stress caused the down-regulation of genes involved in photosynthesis and carbon fixation and the up-regulation of genes involved in stress responses, and amino acid and lipid breakdown suggesting energy starvation. When transgenic plants expressing ACC deaminase in the roots were exposed to nickel stress, plant stress symptoms were significantly lower and biomass was significantly higher suggesting that lowering the level of ethylene relieved many of the stress symptoms. In fact, genes involved in photosynthesis, secondary metabolism and nitrate assimilation were up-regulated in transgenic plants compared with non-transformed plants in the presence of nickel, suggesting that ACC deaminase is effective at reducing the severe effects of this metal stress.

>Magister Scientiae - MSc / In an ever changing environment, plants are constantly challenged by various abiotic stresses such as salinity, which limits global crop production. This directly affects food availability for the global population, which is projected to increase to 9.5 billion by 2050, which in turn places great pressure on natural resources and food security. These environmental adversities induce the accumulation of reactive oxygen species (ROS) hydrogen peroxide, hydroxyl and superoxide radicals which cause severe oxidative damage to plants. The equilibrium between the production and detoxification of ROS is then dependent on the modulation of enzymatic and non-enzymatic antioxidants to achieve plant homeostasis. / 2024

Magister Scientiae - MSc (Biotechnology) / The yearly increase of global population will result in a greater demand for crop production, but with the climates changes and a lack of available agricultural land it will become increasingly more difficult to provide sufficient crops to feed everyone adequately. Application of the PGPE has proven over the past researches to be able enhance growth of plants via various growth promoting mechanisms. To identify suitable growth promoting bacteria candidate, E. plantagineum plant was used to isolate endophytes from the root after surface sterilization. The isolates bacteria were used to inoculate Brassica napus L seeds. The effects of isolate's ability to promote growth were evaluated based on the certain growth parameters after 42 days in the green house. Isolate CP5 produced highest results in all growth parameter. Isolates CP5 was selected as potential candidate as significant improvement was shown by this isolate. This isolate was tested for the ability to produce ACC deaminase, solubilize phosphate, synthesize IAA and siderophore production. Furthermore isolate CP5 growth promotion abilities was tested on Brassica napus L under antimony stress. / 2021-08-31

L'intensification des activités industrielles et les besoins en énergie font des hydrocarbures pétroliers (HP) un enjeu majeur mondial mais augmentent aussi considérablement les risques environnementaux dans divers écosystèmes. La phytoremédiation est une phytotechnologie qui a fait ses preuves en tant que solution verte pour faire face aux contaminations des sols par des HP. La phytoremédiation des sols contaminés par les HP repose principalement sur l’activité des communautés microbiennes associées aux racines des plantes au niveau de la rhizosphère, qui peuvent non seulement favoriser la croissance des plantes hôtes mais aussi augmenter leur tolérance à divers stress biotiques et abiotiques. Parmi les défis majeurs de la phytoremédiation des sols contaminés par les HP, on compte la forte toxicité de certains composés des HP qui entravent la croissance des plantes et par conséquent l’efficacité de la phytoremédiation. Cependant, la croissance des plantes peut être positivement stimulée par la présence de rhizobactéries favorisant leur croissance (PGPR) qui sont capables d'atténuer le stress des plantes par divers mécanismes. Dans cette thèse, un total de 438 bactéries PGPR dégradant les hydrocarbures pétroliers, ont été isolées de la rhizosphère et du sol de deux espèces de plantes, Salix purpurea et Eleocharis obusta, dans un site d'une ancienne raffinerie pétrochimique à Varennes, QC, Canada. Les isolats bactériens ont été classés en 62 genres, appartenant aux phylums Actinobacteria, Bacteroidetes, Firmicutes et aux sous-groupes Alpha-, Beta- et Gamma-Proteobacteria. De plus, cette collection de cultures contient 438 isolats bactériens avec de multiples caractéristiques de dégradation et de stimulation de croissance (PGPR), représentant une diversité fonctionnelle de dégradation des HP et de caractéristiques PGPR qui pourraient être utilisées dans la phytoremédiation assistée par les bactéries, des sols contaminés par les HP. Parmi ces 438 isolats bactériens, 50 isolats représentant une large diversité taxonomique, ont été sélectionnées pour une caractérisation approfondie supplémentaire concernant leur capacité à favoriser la croissance des plantes en présence de différentes concentrations de n-hexadécane (0%, 1%, 2%, 3%) dans des conditions contrôlées. Les résultats ont indiqué que les isolats bactériens Nocardia sp. (WB46), Pseudomonas plecoglossicida (ET27), Stenotrophomonas pavanii (EB31), Bacillus megaterium (WT10) et Gordonia amicalis (WT12) ont significativement augmenté la croissance des plantes cultivées dans 3% de n-hexadécane par rapport au traitement témoin. De plus, ces isolats possèdent plusieurs traits favorisant la croissance des plantes (PGPR) tels que l'activité 1-aminocyclopropane-1-carboxylate (ACC) désaminase (ACCD), la production d'acide indole-3-acétique (IAA) et la fixation de l'azote. De plus, ces isolats étaient capables d'utiliser le n-hexadécane comme seule source de carbone et possédaient des gènes cataboliques liés à la dégradation des hydrocarbures tels que le gène de l'alcane monooxygénase (alkB), le cytochrome P450 hydroxylase (CYP153) et le gène de la naphtalène dioxygénase (nah1). Nocardia sp. isolate WB46, a été sélectionné pour le séquençage de son génome afin de déterminer sa diversité génétique et fonctionnelle relatives à la dégradation des HP et les potentiels PGPR. Les résultats ont indiqué que, sur la base des analyses du gène de l'ARNr 16S, l'hybridation ADN-ADN in silico (DDH) et l'identité moyenne des nucléotides (ANI), Nocardia sp. isolate WB46 représente une nouvelle espèce bactérienne. De plus, l'annotation fonctionnelle de son génome révèle que celui-ci contient de nombreux gènes responsables de la dégradation des hydrocarbures pétroliers tels que l'alcane 1-monooxygénase (alkB) et la naphtalène dioxygénase (ndo) ainsi que d'autres gènes liés à ses potentiels PGPR. En conclusion, la rhizosphère des espèces S. purpurea et E. obusta poussant dans un site fortement pollué par les HP représente un biotope diversifié et comprenant des bactéries PGPR avec de multiples potentiels de dégradation des HP. De plus, plusieurs isolats bactériens tels que Nocardia sp. (WB46), Pseudomonas plecoglossicida (ET27) et Stenotrophomonas pavanii (EB31) démontrent un potentiel d'utilisation comme bioinoculants pour de futures études de phytoremédiation à grande échelle. / Petroleum hydrocarbons (PHCs), as a result of intensification of industrial activities, are a global environmental issue especially in soil environments. Phytoremediation represents an ideal solution to tackle this global crisis. Phytoremediation of PHC-contaminated soils proceeds mainly through the activities of microbial communities that colonize the plant rhizosphere which might promote host plants growth and increase its tolerance to various biotic and abiotic stresses. A main challenge in phytoremediation of PHC-contaminated soils is the high toxicity of PHCs which hinder plant growth and reduce the efficiency of phytoremediation. However, plant growth may be positively stimulated by the presence of plant growth-promoting rhizobacteria (PGPR) that are able to alleviate stresses in plants through various mechanisms. In this thesis, a total of 438 petroleum hydrocarbons degrading-PGPR bacterial isolates were recovered from the rhizosphere and the surrounding bulk soil of Salix purpurea and Eleocharis obusta plants from the site of a former petrochemical plant in Varennes, QC, Canada. Bacterial isolates were classified into 62 genera, belonging to the phyla Actinobacteria, Bacteroidetes, Firmicutes and the Alpha, Beta and Gamma-subgroups of Proteobacteria. Additionally, this culture collection holds 438 bacterial isolates with multiple degradative and PGP features, representing a rich reservoir of metabolically versatile PGPR-PHC degraders that could be used in holistic, bacterial-aided phytomanagement of PHC-contaminated soils. Among the above 438 bacterial isolates, 50 bacterial strains representing a wide phylogenetic range were selected for an additional in-depth characterization regarding their ability to promote plant growth under the presence of different concentrations of n-hexadecane (0%, 1%, 2%, 3%) under gnotobiotic conditions. Results indicated that bacterial isolates Nocardia sp. (WB46), Pseudomonas plecoglossicida (ET27), Stenotrophomonas pavanii (EB31), Bacillus megaterium (WT10) and Gordonia amicalis (WT12) significantly increased the growth of plants grown in 3% n-hexadecane compared with the control treatment. Additionally, these isolates possess several plant-growth-promoting (PGP) traits such as 1-aminocyclopropane-1-carboxylate (ACC) deaminase (ACCD) activity, indole-3-acetic acid (IAA) production and nitrogen fixation. Also, these isolates were able to use n-hexadecane as sole source of carbon and have catabolic genes related to hydrocarbon degradation such alkane monooxygenase (alkB) gene, the cytochrome P450 hydroxylase (CYP153) and the naphthalene dioxygenase (nah1) gene. The isolate that showed the highest growth stimulation of plants grown in 3% n-hexadecane under gnotobiotic conditions, Nocardia sp. isolate WB46, was selected for de novo genome sequencing to unveil its genetic versatility and the mechanisms of PHCs biodegradation and PGP potentials. Results indicated that based on the 16S rRNA gene analyses, in silico DNA-DNA hybridization (DDH) and average nucleotide identity (ANI) Nocardia sp. isolate WB46 is a new species. Additionally, the functional annotation of the genome of Nocardia sp. isolate WB46 reveals that its genome contains many genes responsible for petroleum hydrocarbon degradation such as alkane 1-monooxygenase (alkB) and naphthalene dioxygenase (ndo) as well as other genes related to its PGP potentials. In conclusion, S. purpurea and E. obusta growing in a site highly polluted with PHCs are rich reservoir of diverse PGPR with multiple PHC-degradation and PGP potentials. In addition, several bacterial isolates such as Nocardia sp. (WB46), Pseudomonas plecoglossicida (ET27) and Stenotrophomonas pavanii (EB31) demonstrate potential for use as bioinoculants in future large-scale phytoremediation studies.