Post Bachelors RA Pacific Northwest National Laboratory Kennewick, Washington
Body of Abstract: The plant microbiome, including microbial endophytes living within plants, has a significant influence on the productivity and resilience of the host plant. However, the molecular mechanisms controlling endophyte-plant interactions have not been thoroughly characterized in trees. This work seeks to identify the underlying molecular mechanisms in Populus spp.-diazotrophic endophyte interactions. We used Burkholderia vietnamiensis (WPB) as an endophytic bacteria isolated from Populus trichocarpa, which can fix nitrogen independently without a host plant present. However, in the presence of the host, we hypothesized that P. trichocarpa regulates nitrogen fixation through an exchange of metabolites with WPB under environmental changes such as drought. Using liquid chromatography mass spectrometry (LCMS), we identified 34 compounds in poplar root exudates which were variably produced under drought and well-watered conditions. To further characterize this interaction, we employed a 2-dimensional sterile microfluidic synthetic soil habitat known as a ‘Rhizochip’ and imaged the expression of a fluorescent transcriptional reporter fused to a nitrogen fixing gene (nifH) of WPB cells within the plant root tissue. Our approach showed a unique physical interaction of WPB in the root elongation zone within the root epidermal cells as well as a heterogenous expression of nifH within root tissues. The use of matrix-assisted laser desorption ionization - mass spectrometry imaging (MALDI-MSI) allowed us to monitor the spatial distribution of metabolites exchanged between the plant root and bacterial endophytes, including various nitrogenous metabolites in different root regions. Using such a multidisciplinary approach, this work will advance our understanding of molecular mechanisms controlling endophyte-poplar interactions that can best prime plant pathways for enduring abiotic stresses and increase environmental sustainability and fitness of bioenergy crops.