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Degree Name

Doctor of Philosophy in Quantitative Biology



First Advisor

Woo-Suk Chang


The formation of specialized root organs known as nodules is the most defining characteristic of leguminous plants due to the fixation of atmospheric nitrogen to bioavailable forms enabled by rhizobial endosymbionts. This relationship has played an integral role in the agricultural practice of using such crop plants as biofertilizers to reduce the use of and dependency on synthetic chemical fertilizers. Tropical legumes, such as members of the genus Aeschynomene, are particularly recognized for their ability to form stem nodules through an unknown mechanism independently of the canonical Nod Factor signaling pathway used in standard root nodulation. The works in this study have identified the significance of the Bbta_p0110 gene from the NF-independent nodulating Bradyrhizobium sp. BTAi1 in nodulation of the plant Aeschynomene indica under laboratory conditions. In addition to nitrogen fixing nodule symbionts, these organs house a range of plant growth promoting endophytic bacteria that confer traits such as nutrient acquisition, disease resistance, phytohormone production, and abiotic stress tolerance. These endophytic bacteria are specific to the regions in which the host plant is cultivated. There have been many studies demonstrating host/symbiont specificity depending on species and region. However, none have demonstrated host specificity of the same plant species, particularly A. indica depending on geographical origin. In this study, we show a clear difference in host plant response to endophytic bacteria obtained from varying geographical regions and plant growth promotion indicating biogeographic importance on host/endophyte symbiosis. Additionally, we isolated and identified a novel nodule promoting Leifsonia bacterial species and, through whole genome sequencing, have postulated its role as an abiotic stress mitigator for A. indica and other significant crop plants. Insights to the dynamics of endophyte and host plant relationships regarding nodulation, nutrient cycling, and stress tolerance leads to further advancements and understanding behind the use of bacterial inoculants as biological fertilizers for agricultural purposes.


Nodulation, Endophytes, Plant-Microbes, NF, Nod Factors, NF- independent, Independence, Symbiosis, Nodules, Stem, Stemnodules, Aeschynomene, Aeschynomene indica, BTAi1, Bradyrhizobium BTAi1


Biology | Life Sciences


Degree granted by The University of Texas at Arlington

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