Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Biology

Supervisor

Kohalmi, Susanne E.

Abstract

Phenylalanine (Phe) is an essential aromatic amino acid synthesized by plants and the final reaction in its biosynthesis is catalyzed by AROGENATE DEHYDRATASEs (ADTs). In Arabidopsis thaliana, six isoforms (AtADT1-ADT6) are capable of performing this reaction. To analyze the expression patterns of each AtADT, in silico data were used to describe AtADT mRNA expression during development in A. thaliana and Solanum lycopersicum (tomato). Eight stable A. thaliana transgenic lines with ADT promoter-eGFP/GUS reporter constructs were also tested and analyzed under standard conditions during development. This showed that AtADTs are differentially regulated through their promoters, which results in the variation of their expression. ADT expression patterns were described and putative roles in channeling carbon to different Phe-derived metabolites were proposed for each ADT, associating expression data in plant organs with different Phe-derived metabolites. This thesis is a valuable information resource and foundation for future high-resolution studies of ADT expression.

Summary for Lay Audience

Plants provide a wide assortment of nutrients to the animals that consume them. One such critical nutrient resource are the amino acids, the building blocks of cellular proteins. As some amino acids (the so-called "essential" amino acids) cannot be made by animals, they must obtain them from external sources (ultimately plants) to survive. One essential amino acid, phenylalanine (Phe), not only acts as an important component of proteins, but also serves as a chemical precursor that is needed for the synthesis of compounds important for plant colours, scents, cell strength, and plant protection, as well as animal neurotransmitters. Thus, understanding how Phe is made is of the utmost importance to both plant and animal science. Arabidopsis thaliana, a small, flowering plant commonly used as a model organism for studying plant biology, has six proteins called AROGENATE DEHYDRATASEs (ADTs) that are essential for making Phe. Interestingly, each of the six ADTs behaves differently, as they are seen in different organs at different times at differing levels. These differences have been linked to “promoters”, sequences of DNA that control when and where ADTs are made in response to internal, developmental, or environmental stimuli. To understand what each ADT promoter does, this thesis describes when and where ADTs are made in the different parts of a plant, over the course of plant development. First, using computer software, A. thaliana ADT expression was described and compared to each other ADT. This resulted in a comprehensive depiction of ADT expression during development, which was also compared to the expression patterns of ADTs defined in tomatoes. Finally, ADT expression was directly assayed using A. thaliana plants that were engineered to express chemical markers that show where an ADT of interest is made. Using this reporter approach, the expression of each ADT was described for roots, leaves, stems, and flowers. This resulted in the proposal that individual ADTs have roles in making Phe-derived products that are important for the organs in which the ADT is expressed. The information and the reporter plants generated in this thesis are vital for the understanding of how ADTs affect Phe synthesis.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Available for download on Saturday, April 30, 2022

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