| dc.description.abstract | Water is a major limiting resource in agriculture worldwide, restricting crop yields in approximately 70 percent of arable farmlands. My goal was to alleviate drought stress in grasses using plant growth-promoting rhizobacteria (PGPR) and host-mediated microbiome engineering (HMME) of the rhizosphere. In the summers of 2016 and 2017, we collected bermudagrass rhizospheres from El Paso, TX for PGPR bioprospecting. Two novel isolates, Bacillus sp. (12D6) and Enterobacter sp. (16i) , were shown to delay the onset of drought stress in wheat (Triticum aestivum subsp. aestivum cultivar TAM 111) and maize (Zea maize cultivar B73) seedlings. Roots inoculated with these PGPR resulted in statistically significant alterations in root system architecture traits associated with drought tolerance in a host-specific manner. In the second part of this study, I employed host-mediated microbiome engineering to confer a generational increase in drought tolerance of wheat seedlings. In this host-centric artificial selection process, the wheat rhizosphere was sub-selected based on host phenotypic tolerance after a prolonged water deficit. After six rounds of microbiome engineering, seedlings growing in the engineered microbiome withstood an additional 5 days of water deficit compared to the initial microbiome. The engineered microbiome demonstrated statistically significant alterations in root system architecture and increases in water retention. Next generation sequencing of rounds 0, 3, and 6 using the 16S rRNA gene followed by bioinformatic analyses revealed taxonomic increases in Proteobacteria at the phylum level and Betaproteobacteria at the class level, progressively decreasing α – diversity of bacterial community, and changes in the functional metagenome for cell motility, signaling, and metabolism. Overall, findings from both studies improve the understanding of the ecological and evolutionary implications of plant-microbe interactions in a water deficient environment, with potential applications that can be directly used for mitigating drought stress in cereal crops. | en |
