No description available.

Arbuscular mycorrhizal fungi (AMF) form a mutually beneficial symbiotic relationship with a majority of land plants through an exchange of nutrients. Despite the importance of AM symbiosis in agricultural and ecological settings, relatively little is known about how the fungal symbiont actively promotes symbiosis. To overcome a host’s immune response, plant pathogens secrete effector proteins that modify a host to suppress an immune response. Few effectors have been identified in AMF, as bioinformatics methods have failed to accurately predict their sequences. To successfully colonize a plant, AMF form structures called arbuscules within plant root cortical cells. Arbuscules are a primary site of nutrient exchange during AMF symbiosis. This work is built on the hypothesis that AMF produce effector proteins to promote symbiosis, and that arbuscules are a site of effector secretion. Using Rhizophagus irregularis, Glomus versiforme and Medicago truncatula this work applies a proteomics-based approach using a new biotechnology to identify fungal proteins secreted by AMF. This novel approach using proteomics and proximity labelling to identify proteins by mass spectrometry is the first time this system has been used to study the plant-AMF relationship. In this work, mass spectrometry identifies a total of 24 R. irregularis proteins and two G. versiforme proteins that are candidate effectors involved in the plant-AMF symbiosis.

Numerous soils have been contaminated by radiocaesium (Cs) as a result of nuclear weapon testing and accidents at nuclear power-plant facilities. Management of the areas, which have been exposed to either intense or diffuse Cs pollution, has therefore become a major environmental concern. Strategies orientated toward the use of plants and microorganisms, or both in combination, have been proposed in the recent years as potential players in removing or stabilizing Cs in contaminated soils. Among these microorganisms, arbuscular mycorrhizal (AM) fungi are of particular interest due to their unique position at the soil/root interface and their recognized role in element transport and immobilization. In the recent years, contradictory results have been published on the impact of AM fungi on Cs accumulation by plants, failing to ascertain whether AM fungi could effectively transport this radionuclide to their host. Therefore, the objective of this work was to determine the role of AM fungi in plant Cs acquisition and accumulation. Using in vitro compartmented systems, we unambiguously demonstrated that AM fungi could transport Cs to their host, while its accumulation within the extraradical mycelium was rather limited. Our results also suggested that AM fungi could have an effect on Cs distribution within their host. Indeed, it appeared that AM fungi could potentially limit the translocation of Cs from roots to shoot. However, if the results obtained during this research project have shown that AM fungi could influence the acquisition and accumulation of Cs by plants, their capacity to take part in phytoremediation strategies remains questionable and would need additional investigations. In particular, attention should be focused on the mechanisms behind Cs transport by AM fungi, their influence on Cs root to shoot translocation and the subsequent validation of the findings obtained to in situ conditions.

Microorganisms and their interactions in soil play a critical role in nutrient transformations and cycling, and in sustaining soil productivity. Arbuscular mycorrhizal fungi (AMF) are a keystone group of fungi influencing nutrient cycling. In turn, the activity and composition of microorganisms in soil are influenced by management practices such as the choice of crop species and fertilization. Long-term effects of cropping, manuring and mineral fertilization on the soil-plant system were defined in three selected agro-ecosystems of Canada. A greenhouse experiment was also conducted to define the involvement of AMF in organic residue decomposition and nitrogen (N) mineralization.<p> In the greenhouse experiment, pasteurized soil was inoculated or not with a strain of <i>Glomus claroideum, G. clarum</i> or <i>G. intraradices</i>. 15N-labelled organic residue in a nylon mesh was buried in the soil. The fate of residue-N was determined after 24 weeks. Arbuscular mycorrhizal fungal species enhanced mineralization of organic residue to different degrees. The highest recovery of mineralized N by plants (25%) occurred when inoculated with <i>G. clarum</i>. The AMF enhanced N-mineralization differentially leading to differential plant growth stimulation, differences in the C-to-N ratio of the decomposing organic residue, and in soil microbial community structure.<p> In a field trial conducted on a Brown Chernozemic soil at the Semiarid Prairies Agricultural Research Centre in Swift Current, SK, eight years of phosphorus (P) (0, 20 and 40 kg P2O5 ha-1) application to alfalfa monoculture and alfalfa-Russian wildrye (RWR) dual culture modified the soil microbial community structure. Low levels of phosphorus (0 and 20 kg P2O5 ha-1) fertilization in alfalfa-RWR dual culture increased the abundance of fungivorous nematodes and grazing of AMF hyphae thus increasing the carbon drain from plants and ultimately reducing plant biomass.<p> In a sub-humid region of Saskatchewan on a a Black Chernozem soil, mineral N (0, 20 or 40 kg N ha-1) was applied for 10 years to pea grown continuously or in rotation with wheat. Lower yields in continuous-pea were associated with reduced abundance of beneficial Gram positive bacteria and AMF, and an increase in uptake of plant available Fe to toxic levels. These differences in soil properties were related to root rot which increased with years in continuous-pea. The soil environment in the continuous-pea rotation further led to lower organic carbon inputs, and to reduced soil microbial biomass and soil enzyme activity indicating a negative impact on nutrient cycling.<p> In the south coastal region of Agassiz, British Columbia, dairy manure slurry (DMS) and ammonium nitrate (AN) had been applied on a Regosol at the same annual rate of mineral N (50 or 100 kg mineral N ha-1) for nine years to perennial tall fescue, followed by one year of stand renovation through reseeding without fertilization. The multi-year application of DMS improved soil organic C, soil organic N, light fraction of organic matter, microbial biomass and enzyme activity as compared to mineral fertilization but the DMS-related increase in soil yield potential was lost in the process of stand rejuvenation. Dairy manure slurry application based on the crop N requirement also increased soil phosphate indicating increased environmental hazard. In conclusion, long-term use of DMS in multi-cut tall fescue can increase soil quality parameters but can also increase the risk of eutrophication of water bodies.<p> Overall, data showed that higher levels of soil nutrients can select for certain bacteria while AMF and other bacteria are more abundant under low soil fertility. On the other hand, different soil microbial groups were associated with different soil enzyme activities. From this study, I succeded in proving my hypothesis that practice of fertilization and choice of crop influence soil microbial community structure which further affect soil functioning.

Microorganisms and their interactions in soil play a critical role in nutrient transformations and cycling, and in sustaining soil productivity. Arbuscular mycorrhizal fungi (AMF) are a keystone group of fungi influencing nutrient cycling. In turn, the activity and composition of microorganisms in soil are influenced by management practices such as the choice of crop species and fertilization. Long-term effects of cropping, manuring and mineral fertilization on the soil-plant system were defined in three selected agro-ecosystems of Canada. A greenhouse experiment was also conducted to define the involvement of AMF in organic residue decomposition and nitrogen (N) mineralization.<p> In the greenhouse experiment, pasteurized soil was inoculated or not with a strain of <i>Glomus claroideum, G. clarum</i> or <i>G. intraradices</i>. 15N-labelled organic residue in a nylon mesh was buried in the soil. The fate of residue-N was determined after 24 weeks. Arbuscular mycorrhizal fungal species enhanced mineralization of organic residue to different degrees. The highest recovery of mineralized N by plants (25%) occurred when inoculated with <i>G. clarum</i>. The AMF enhanced N-mineralization differentially leading to differential plant growth stimulation, differences in the C-to-N ratio of the decomposing organic residue, and in soil microbial community structure.<p> In a field trial conducted on a Brown Chernozemic soil at the Semiarid Prairies Agricultural Research Centre in Swift Current, SK, eight years of phosphorus (P) (0, 20 and 40 kg P2O5 ha-1) application to alfalfa monoculture and alfalfa-Russian wildrye (RWR) dual culture modified the soil microbial community structure. Low levels of phosphorus (0 and 20 kg P2O5 ha-1) fertilization in alfalfa-RWR dual culture increased the abundance of fungivorous nematodes and grazing of AMF hyphae thus increasing the carbon drain from plants and ultimately reducing plant biomass.<p> In a sub-humid region of Saskatchewan on a a Black Chernozem soil, mineral N (0, 20 or 40 kg N ha-1) was applied for 10 years to pea grown continuously or in rotation with wheat. Lower yields in continuous-pea were associated with reduced abundance of beneficial Gram positive bacteria and AMF, and an increase in uptake of plant available Fe to toxic levels. These differences in soil properties were related to root rot which increased with years in continuous-pea. The soil environment in the continuous-pea rotation further led to lower organic carbon inputs, and to reduced soil microbial biomass and soil enzyme activity indicating a negative impact on nutrient cycling.<p> In the south coastal region of Agassiz, British Columbia, dairy manure slurry (DMS) and ammonium nitrate (AN) had been applied on a Regosol at the same annual rate of mineral N (50 or 100 kg mineral N ha-1) for nine years to perennial tall fescue, followed by one year of stand renovation through reseeding without fertilization. The multi-year application of DMS improved soil organic C, soil organic N, light fraction of organic matter, microbial biomass and enzyme activity as compared to mineral fertilization but the DMS-related increase in soil yield potential was lost in the process of stand rejuvenation. Dairy manure slurry application based on the crop N requirement also increased soil phosphate indicating increased environmental hazard. In conclusion, long-term use of DMS in multi-cut tall fescue can increase soil quality parameters but can also increase the risk of eutrophication of water bodies.<p> Overall, data showed that higher levels of soil nutrients can select for certain bacteria while AMF and other bacteria are more abundant under low soil fertility. On the other hand, different soil microbial groups were associated with different soil enzyme activities. From this study, I succeded in proving my hypothesis that practice of fertilization and choice of crop influence soil microbial community structure which further affect soil functioning.

No description available.

Arbuscular mycorrhizal (AM) fungi are a group of fungi that are able to establish a symbiotic relationship with the root system of many land plants. This symbiosis improves plant fitness by increasing the uptake of crucial mineral nutrients, particularly phosphorus and nitrogen. In return, the fungi receive organic carbon from the plant host in the form of sugars and lipids. The objective of my research is to assess whether the Nitrate and Peptide Transporter Family (NPF) of transport proteins play a role in mediating AM symbiosis. Firstly, we explored the involvement of NPF genes NPF1B and NPF4.12 by examining the phenotype of Medicago truncatula mutants. Secondly, we employed a modified yeast two-hybrid system to determine the phytohormone import capabilities of these NPF transport systems. Lastly, we employed reporter gene fusions to assess the spatial and temporal expression profiles of these NPF genes. The results of our research do not support our hypothesis that these NPF genes play a role in mediating AMF symbiosis. The results of the modified yeast-two hybrid tests revealed abscisic acid (ABA) and gibberellic acid (GA3) import capabilities of the transport system encoded by the gene NPF4.12. Future study of the diverse mechanisms that underpin AM symbiosis will nonetheless be useful to the agricultural industry by reducing farmer's reliance on chemical fertilizers.

Arbuscular mycorrhizal fungi (AMF) provide numerous services to their plant symbionts. Understanding the effects of climate change on AMF, and the resulting plant responses, is a crucial factor in predicting ecosystem responses on a global scale. We used a manipulative climate change experiment embedded within a natural climate gradient in Oregon and Washington to examine how the effects of future climate change on AMF-plant symbioses are mediated by soil water availability, soil nutrient availability, and vegetation dynamics. Using structural equation modeling, we found that the direct effect of increasing temperatures was to decrease AMF colonization. Indirect effects of temperature, mediated through other variables, canceled each other out. However, future shifts in these relationships could either exacerbate or mitigate the negative direct effect of temperature. As ecosystems in Mediterranean climates experience more intense droughts and heavier rains, decreases in AMF colonization could have substantial consequences for plant communities and ecosystem function.

Arbuscular mycorrhizal (AM) fungi are important symbionts to most of the terrestrial plants. Recent genome sequencing projects revealed that many AM fungi have repetitive genetic elements in their genomes and among these repetitive genetic elements, cut-and-paste DNA transposable elements were very prevalent. For example, in Rhizophagus irregularis, up to 21% of the genome assembly content was associated with cut-and-paste DNA transposable elements. In Diversispora epigaea, up to 23% of the genome content can also be attributed to cut-and-paste DNA transposable elements. While cut-and-paste DNA transposable elements are very abundant in AM fungi, detailed studies on these repetitive elements have been lacking. In this study, we revealed the diversity of cut-and-paste DNA transposable elements in Claroideoglomus claroideum and identified many potentially autonomous transposable elements in the genome assembly of C. claroideum. The evolutionary relationship between the DNA transposons we identified and the established sequences in public databases were also investigated.

The present study was aimed to find out if there is any symbioses between C.australe roots and mycorrhizal fungi. This research also aimed to investigate the effect of Arbuscular mycorrhizal fungi on the growth of C.australe and the yield of alkaloid castanospermine. The rhizosphere soil and roots of C.australe from various sites in Sydney were collected. Roots were stained with vital and non-vital stains for assessment of mycorrhizal infection. The result indicated that AM fungi symbiotic associations with the roots of C.australe, producing arbuscules and vesicles in the root cortices. By wet sieving and decanting of rhizosphere soil, spores and sporocarps of AM fungi, were recovered. The spores mainly belonged to the genus Glomus. A correlation study was conducted to determine the relationship between the AM infection percentage in the roots and the Castanospermine amount in the leaves and seeds of the field grown trees. The results showed that there is a positive relationship between the castanospermine amount in the seeds and AM infection percentages in the roots. The effect of phosphorus on the yield of castanospermine was also investigated. The results indicated that phosphorus do enhance castanospermine at certain levels, but a further increase in phosphorus application resulted in reduced AM infection. It was found that AM has a great effect on the growth and production of C.australe and biosynthesis of castanospermine. / Master of Science