Term of Award

Spring 2018

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.


Department of Biology

Committee Chair

John Schenk

Committee Member 1

Kerrie Sendall

Committee Member 2

Christian Cox


Mentzelia section Bartonia (Loasaceae) commonly occurs in some of the hottest and driest places in North America, but we poorly understand the mechanisms that allow them to tolerate such extreme environments. Morphological and physiological adaptations are well studied in model organisms. The underlying genetic responses to drought stress in non-model organisms like Mentzelia is unknown. To better understand and identify differences and similarities in genetic responses to drought stress between species existing in different habitats with differing water availability, three species from the genus Mentzelia were compared. Species of section Bartonia occur across an environmental gradient, from temperate to arid habitats, allowing for us to apply a comparative approach to quantify the genetic response of drought across an environmental gradient. In order to determine genetic differences between arid, intermediate, and temperate adapted species of Mentzelia in response to drought, we created genomic tools for use in differential gene expression analysis. Two de novo reference transcriptomes from five tissues (roots, stems, leaves, flowers, and fruits) were generated with Trinity. Four controls and four treatment plants were collected from three species: M. filifolia, M. reverchonii, and M. speciosa. Leaf and root tissues were collected from control and drought shocked plants. Treatment plants were removed from the ground and laid in full sun for one hour to simulate acute drought. We sequenced the set of expressed genes from root and leaf tissues and analyzed them for differential gene expression. BWA, SAMtools, Corset, and edgeR were used for read alignment, cluster counts, and differential gene expression analysis. We identified 165 differentially expressed clusters across all three species, and 140 clusters were annotated to known genes using Blast2GO. The transcriptome profiling approach was coupled with a target genes approach that measured expression of 90 genes associated with drought tolerance in model organisms. Mounted genetic responses were greater in arid-adapted species compared to the temperate species, with differences in leaf and root tissue responses. We found that that leaves up-regulated protein degradation and down-regulated senescence pathways, while roots up-regulated cellular respiration and down-regulated photosynthetic processes. Target genes revealed differences and similarities between functional processes taking place within Mentzelia and other plant groups in response to drought stress. Twelve target genes were identified in our dataset out of 90, which included regulation of dehydrin, NAC domains, aquaporins, and auxin transport. As climates change to become hotter and drier, it is becoming increasingly important to understand how plants in arid environments tolerate limited water resources. We found that drought tolerance is enhanced through pathways of delayed senescence and that genetic responses were tissue and habitat specific.

Research Data and Supplementary Material