Date of Award
8-2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Plant and Environmental Science
Committee Chair/Advisor
Vidya Suseela
Committee Member
Barbara Campbell
Committee Member
Nishanth Tharayil
Committee Member
William Bridges
Abstract
Arbuscular mycorrhizal fungi (AMF) are obligate biotrophs forming symbiotic association with plants. The plant-AMF symbiosis has gained much attention due to its ability to improve plant nutrient uptake, especially phosphorus, which is often inadequately available to plants due to its limited mobility and complex formation in many soils. Phosphorus (P) is a crucial nutrient for plants, and most phosphate fertilizers are derived from phosphate rock, a finite natural resource. Thus, optimizing P uptake is vital for sustaining crop yields and addressing the needs of a growing global population. Plant-AMF symbioses are significant in this context, as AMF can acquire P from phosphorus-limited soils through their extensive hyphae. In exchange, plants supply carbon to promote AMF growth, establishing a mutually beneficial symbiotic association. However, various factors, including the species of plants and AMF, along with the environmental conditions under which the symbiosis occurs, can affect the effectiveness of this symbiosis. Therefore, understanding the biotic and abiotic factors that influence the symbiotic efficiency is essential for designing effective management strategies for using AMF in agroecosystems.
This dissertation investigates the primary drivers affecting the plant-AMF symbiosis by probing the molecular cross-talk between plants, AMF, and the surrounding soil microbiome in phosphorus-limited settings. The first objective was to evaluate how various sorghum genotypes, differing in their inherent root traits that affect P acquisition efficiency (biotic factor), and the stratified nutrient availability (an abiotic factor), impact plant-AMF symbiotic efficiency and hence the outcome of this symbiosis. A greenhouse experiment was conducted with multiple sorghum genotypes under stratified and uniform phosphorus conditions, both with and without AMF inoculation. The study examined the trade-offs among different phosphorus-acquisition strategies (root growth, root metabolite production, and mycorrhizal symbiosis) and the resulting changes in root metabolomes. The results indicated that AMF treatments altered phosphorus-acquisition strategies irrespective of the plant genotype (whether P-efficient or P-inefficient). All sorghum accessions inoculated with AMF demonstrated greater tissue phosphorus content and shoot biomass than control plants without mycorrhiza. Furthermore, colonization by AMF influenced both the primary and specialized metabolite profiles in roots, as well as root morphology, facilitating a functional plant-AMF symbiosis. Notably, plants in stratified phosphorus environments benefited more from AMF colonization than those in uniform phosphorus conditions, highlighting the vital role of AMF in accessing localized phosphorus-rich areas. This observation is particularly pertinent given phosphorus's low mobility and patchy distribution in most soils. Additionally, the influence of other soil microorganisms on phosphorus availability and AMF effectiveness led to further exploration of the broader soil microbiome.
Thus, the second study in this dissertation aimed to analyze the metabolite profiles from both roots and AMF hyphae, as well as examine the microbiome associated with plant roots (rhizosphere microbiome) and AMF hyphae (hyphal microbiome). For this research, a greenhouse mesocosm experiment using sorghum genotypes with varying root exudate profiles was established, with either Rhizophagus intraradices, Gigaspora margarita, or an uninoculated control (non-mycorrhizal). The experiment setup included separate compartments for roots and hyphae to assess how plant and fungal exudates affect microbiome composition. The goal was to determine how various combinations of AMF species and host genotypes shape the hyphal microbiome and affect symbiotic performance. The findings demonstrated that the soil metabolite profiles of the AMF and the plant root compartments differed. The bacterial communities were also different in the hyphosphere and rhizosphere compartments. It was also noted that AMF-inoculated plant roots selectively attracted mycorrhizal helper bacteria, potentially enhancing the symbiotic efficiency. These findings emphasize the critical role of soil microbial communities in enhancing AMF-mediated nutrient uptake and their significance in the success of plant-AMF partnerships.
The third and final study of this dissertation examined lipid dynamics within the plant-AMF symbiosis, an area of increasing interest following recent discoveries that AMF are lipid auxotrophs depending on their host plants for lipid supply. By using root and hyphae samples from the same greenhouse mesocosm experiment described earlier, lipidomic analyses were performed to assess the impact of symbiotic relationships between three different sorghum genotypes and two AMF species (R. intraradices and G. margarita), including a non-inoculated control, on lipid composition. The results showed variability in lipid profiles associated with different AMF species. R. intraradices displayed broader upregulation of lipid species across both roots and hyphae, indicating a more metabolically active interaction. Both AMF species had higher abundance of storage lipids such as triglycerides and diglycerides, indicating a higher carbon requirement for extensive hyphal growth and spore production. The roots and hyphae showed distinct lipid profiles, with AMF-inoculated roots exhibiting a higher abundance of several lipid species not observed in non-inoculated control roots. These findings reveal the functional diversity in lipid accumulation among various AMF species and underscore the importance of lipids in mediating plant-AMF symbiosis.
In conclusion, this dissertation enhances our understanding of the plant-AMF symbiosis by offering important insights into the complex interactions among host plants, AMF species, and soil microbial communities under limited P availability.
Recommended Citation
Gill, Jasmine, "Elucidating the Mechanisms Underlying a Functional Plant-Arbuscular Mycorrhizal Symbiosis Using Omics Approaches" (2025). All Dissertations. 3974.
https://open.clemson.edu/all_dissertations/3974
Author ORCID Identifier
https://orcid.org/0009-0006-8238-0538