Date of Award
Doctor of Philosophy (PhD)
School of Biological Sciences
The overall goal of this thesis was to genetically improve agronomic traits of pennycress (Thlaspi arvense L.; Field Pennycress) and demonstrate the production of value-added designer seed oils to domesticate pennycress and enable its establishment as a new winter annual oilseed/meal/cover crop to be grown in temperate regions of the world. In the U.S. Midwest, pennycress can be double cropped on existing farmland during the time between corn harvest and subsequent planting of soybeans the following spring. Pennycress has the potential to produce 2,000 lbs/acre seeds, which at 33% by weight oil content and 20% protein, would yield 85 gallons/acre oil e.g. for conversion to biofuels and 1,300 lbs/acre press-cake for use e.g. as a high-protein animal feed meal supplement. While pennycress holds much agronomic promise, the seed coats of wild pennycress strains have a high indigestible fiber content, which makes the seed meal less nutritional than that of canola. Also, wild strains are hampered by seed pods that readily break open (pod shatter) when mature, resulting in significant pre-harvest seed loss. Accumulated triacylglycerols (TAGs) in the embryos of pennycress seeds are high in very long chain fatty acids (VLCFAs) and contain no medium chain fatty acids (MCFAs C6-C14). Oils high in MCFAs are desirable for consumer products and industrial applications and require minimal processing for use in biojet fuel and biodiesel. Here, I show that mutations generatedthrough ethyl methanesulfonate (EMS) mutagenesis and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas9 gene editing of TRANSPARENT TESTA (TT) genes can reduce pennycress seed coat fiber content by as much as 45%, increase seed oil and protein content by over 10%, and reduce seed dormancy without compromising plant health. Moreover, mutagenesis of putative orthologues to genes known to affect pod shatter in other Brassica species uncovered surprising differences in mutational effects on the degree of shattering compared to what has been reported in e.g. Arabidopsis thaliana. Knockout of the putative ALCATRAZ (ALC) orthologue had no observed effects on pod shatter whereas knockout of ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE 1 (ADPG1) function completely abolished pod shattering. Reintroducing a wild-type ADPG1 gene copy into an adpg1 kncokout mutant resulted in partial pod shatter rescue likely to agronomically-relevant levels. Finally, my dissertation work provides proof of concept that pennycress can be genetically engineered to produce seed oils composed of MCFAs (C6-C14) and acetyl-MCFAs in modest amounts without compromising plant health. Together, these findings can be applied directly to pennycress for its domestication and commercialization as a new oilseed cash cover crop and can form the basis for future work aimed at understanding how pennycress responds to domestication trait changes.
Esfahanian, Maliheh, "Reducing Seed Coat Fiber Content and Pod Shatter, and Engineering Medium Chain Fatty Acids-Containing Oil, in the Oilseed Crop Pennycress ( Thlaspi Arvense L. )" (2021). Theses and Dissertations. 1364.