Dissertation
INVESTIGATING THE ROLE OF LEAF AMINO ACID TRANSPORTERS IN SOURCE AND SINK PHYSIOLOGY OF ARABIDOPSIS THALIANA
Doctor of Philosophy (PhD), Washington State University
01/2017
Handle:
https://hdl.handle.net/2376/117804
Abstract
Nitrogen (N) is an essential nutrient needed in large amounts for plant growth and productivity. Following uptake from the soil, inorganic N is reduced either in roots or leaves to amino acids, which are the major transport form of N in most plants. In Arabidopsis thaliana, N reduction mainly takes place in photosynthetic active source leaves. Most protein amino acids are synthesized in the chloroplasts, where they are used for metabolism or they are exported into the cytosol, and channeled into diverse biochemical pathways. In addition, large amounts of amino acids are loaded into the phloem for N partitioning to developing sinks including young leaves, fruits, and seeds. However, little is known about the molecular mechanisms of amino acid transport across the chloroplast membrane and their import into the phloem. In this dissertation, it is hypothesized that amino acid transporters play key roles in regulating N availability for source and sink metabolism and development, and that their function ultimately controls plant productivity. Since N and C metabolism are tightly co-regulated, it is further predicted that N partitioning processes also influence leaf C metabolism and transport.
This work describes the identification and functional characterization of transporters involved in phloem loading as well as in chloroplast transport of amino acids. First, Amino Acid Permease 8 (AAP8) function in phloem loading was elucidated. Using RNA localization studies, it was found that AAP8 is expressed in the phloem of source leaves. Analysis of aap8 mutants resolved the function of the transporter in source to sink partitioning of amino acids, source N metabolism, plant growth, and seed development. Second, consequences of altered amino acid phloem loading for C fixation, metabolism and transport were examined using the aap8 plants. Finally, UmamiT44 was identified and characterized to function in chloroplast export of amino acids. Using umamit44 knock out plants, the role of the transporter in cellular metabolism and its involvement in source to sink partitioning of amino acids were investigated. Overall, this dissertation resolved the important function of amino acid transporters in both plant N and C metabolism, growth, sink development, and plant productivity.
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Details
- Title
- INVESTIGATING THE ROLE OF LEAF AMINO ACID TRANSPORTERS IN SOURCE AND SINK PHYSIOLOGY OF ARABIDOPSIS THALIANA
- Creators
- James Patrick Santiago
- Contributors
- Mechthild Tegeder (Advisor)Asaph B Cousins (Committee Member)Michael Knoblauch (Committee Member)Raymond W Lee (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Program in Molecular Plant Sciences
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 157
- Identifiers
- 99900581425701842
- Language
- English
- Resource Type
- Dissertation