Browsing by Subject "Natural variation"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Germination studies in Arabidopsis thaliana and Sinapis arvensis : genetical and ecological perspectives(2013-08) Morrison, Ginnie Denise; Linder, C. RandalThe environment can exert strong selective pressures on an organism. When selective pressures on traits differ between environments local adaptation may occur. If there is gene flow between the environments, local adaptation may be slowed or prevented. In plants, particularly weedy ephemerals, germination is a life-history trait that can be a strong determinant on fitness. In this dissertation, I explore the germination traits of two weedy Brassicaceae species, Arabidopsis thaliana and Sinapis arvensis, having populations in different habitats to determine whether germination traits within and between populations vary based on environmental conditions and to assess the extent of local adaptation. In Chapter 1, I assessed which genomic regions of A. thaliana were associated with differences in germination traits due to genotype-by-environment interactions. I performed a genome-wide association study using 100 natural accessions of A. thaliana under four light and nutrient combinations. I found 20 single nucleotide polymorphisms significantly associated with different environments, but none associated specifically with genotype-by-environment interactions. In Chapter 2, I assessed germination traits of S. arvensis collected from agricultural and non-agricultural habitats in the Bitterroot Valley of Montana. I discovered that the agricultural collection studied exhibited significantly different germination timing and amounts than the non-agricultural collections, which were statistically indistinguishable from each other. I also found evidence of a strong maternal effect on germination traits. In Chapter 3, I tested whether patterns of genetic variation between agricultural and non-agricultural collections of S. arvensis supported local adaptation to the two habitats even in the face of gene flow. While I expected to see some genetic differentiation between habitats, as seen in Chapter 2, no genetic differentiation was detected and markers putatively under selection were not associated with a particular habitat. I discuss why this might have occurred even though I have evidence for genetically-based phenotypic differentiation between agricultural and non-agricultural populations of S. arvensis.Item Roles for polyploidy, circadian rhythms, and stress responses in hybrid vigor(2014-05) Miller, Marisa Elena; Chen, Z. JeffreyHybrid plants and animals, like corn and the domestic dog, grow larger and more vigorously than their parents, a common phenomenon known as hybrid vigor or heterosis. In hybrids between Arabidopsis ecotypes or species (in allotetraploids), altered expression of circadian clock genes leads to increased starch and chlorophyll content and greater biomass. In plants and animals, circadian clock regulation plays a key role in optimizing metabolic pathways, increasing fitness, and controlling responses to biotic and abiotic stresses. In the allotetraploids, the increased level of heterosis is likely caused by interspecific hybridization as well as genome doubling. However, it is unknown how genome dosage and allelic effects influence heterosis, and whether additional clock output traits, such as stress responses, are altered in hybrids. In three related projects, the effects of genomic hybridization (including parent-of-origin effects) and genome dosage on heterosis were elucidated. In my first project, I found that although ploidy influenced many traits, including seed and cell size, biomass and circadian clock gene expression were most strongly influenced by hybridization. Additionally, parent-of-origin effects between reciprocal hybrids were frequently observed for many traits. In my second project, I described a unique role for RNA-directed DNA methylation (mainly CHH methylation) in mediating the parent-of-origin effect on expression of the circadian clock gene CCA1 in reciprocal hybrids. Altered CCA1 expression peaks were associated with heterosis of biomass accumulation in the reciprocal hybrids. Lastly, I used transcriptome sequencing in hybrids at different times of day to examine changes in downstream clock-regulated pathways. In the hybrids, many genes in photosynthetic pathways were upregulated, while many genes involved in biotic and abiotic stresses were repressed during the morning and afternoon, respectively. Additionally, natural variation between parents in stress-responsive gene expression was found to be crucial for producing vigorous hybrids. These conceptual advances increase the mechanistic understanding of heterosis, and may guide selection of parents for making better hybrids.