Identifier

etd-11122014-211555

Degree

Doctor of Philosophy (PhD)

Department

Biological Sciences

Document Type

Dissertation

Abstract

Phosphorus is an essential nutrient taken up by plants in the form of phosphate and is a component of key molecules, such as ATP, DNA, and RNA, and is one of the most frequently limiting macronutrients for plant growth. More than 80 % of phosphorus found in soil exists as non-inorganic forms and is unavailable for plant uptake, demonstrating the importance for genes induced to cope with phosphate starvation, including high-affinity phosphate transporters (Phts). Phts are membrane-localized transporters involved in the transport of phosphate and arsenate and have a high capacity for transporting phosphate in areas where phosphate concentrations are low, behaving as the main mechanism of phosphate uptake by plants. The Pht1 family in Arabidopsis thaliana contains nine members, of which AtPht1;1 (Pht1;1) and AtPht1;4 (Pht1;4) have been shown to be the major transporters involved in phosphate acquisition from soil. Membrane transporters often function as oligomeric complexes. In plants, there is evidence that oligomerization of transporter isoforms is an important aspect of transport function and influences dynamic regulation. Prior studies have illustrated the importance of the role of higher-ordered plant membrane transporters in uptake regulation however, the potential oligomerization and functions of oligomerization among Phts has not been formally investigated. This research demonstrates the formation of Pht higher-order structures and suggests a function for this association in phosphate and arsenate uptake. In vivo and in vitro protein interaction assays that comprised of split luciferase complementation of transformed protoplasts, yeast-based split ubiquitin and yeast-two-hybrid assays, and immunoprecipitation assays of root microsomal proteins confirm that Pht1;1 and Pht1;4 form homomeric and heteromeric structures. Furthermore, the mutation of Tyr312 in Pht1;1 was found to disrupt homomeric interactions as well as contribute to an increased phosphate uptake rate that exceeds wild-type capacities by five times. Transgenic plants expressing Pht1;1Y312D were shown to have improved phosphate-deficient and arsenate tolerance compared to Pht1;1-overexpression lines. As interaction and uptake capacities are affected, it is likely that Tyr312 plays a role in the selection and regulation of phosphate and arsenate acquisition.

Date

2014

Document Availability at the Time of Submission

Secure the entire work for patent and/or proprietary purposes for a period of one year. Student has submitted appropriate documentation which states: During this period the copyright owner also agrees not to exercise her/his ownership rights, including public use in works, without prior authorization from LSU. At the end of the one year period, either we or LSU may request an automatic extension for one additional year. At the end of the one year secure period (or its extension, if such is requested), the work will be released for access worldwide.

Committee Chair

Smith, Aaron P.

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