Amino acids are necessary for protein synthesis and specialized metabolism in plants. Yet very little is known about how plants sense and regulate when and where to allocate amino acids to meet the demand for nitrogen in growing tissues. In particular, while characterized in yeast and mammals, no amino acid sensor has been identified in plants. Amino Acid Permease 1 (AAP1) has been previously characterized and was shown to mediate amino acid uptake from the soil. aap1 knockout plants and several EMS mutants affected in AAP1 sequence display enhanced tolerance to toxic concentrations of amino acids. Yet, two of the corresponding variant proteins appear to be functional transporters, effectively dissociating amino acid transport and phenotype. To understand this apparent discrepancy, I precisely studied AAP1 localization of expression at the plant and cellular level, and in specific tissue types of the root where AAP1 function is required for the tolerance phenotype and the amino acid uptake activity. I showed that AAP1 protein is present in the endoplasmic reticulum of the cortex in wild type plants Yet, its ectopic expression in root tip and phloem increased amino acid uptake, while expression in cortex could not. This and other of my results do not support the current model of AAP1 functioning in amino acid uptake by the root. I propose that the main effect of mutations in AAP1 is a disturbance in amino acid metabolism, possibly triggered by altered amino acid sensing. In this new model, AAP1 would be necessary for sensing amino acid status of cortex cells, possibly in the endoplasmic reticulum, and adjust amino acid metabolic activity and uptake to current availability. In effect, disruption of the sensing function, either by complete loss of AAP1 function (knockout) or by uncoupling the transport and sensing function (EMS mutants), would lead to the various characteristics of the phenotype of the aap1 mutants I observed. My main hypothesis is that AAP1 is a transporter endowed with sensing function, i.e., an amino acid transceptor. / Doctor of Philosophy / Changing environments create challenges for plants to grow under harsher, nutrient limiting conditions. Nitrogen is an essential nutrient for plant growth, used for the synthesis of amino acids and other nitrogen-containing metabolites. Amino acids are necessary for protein synthesis and other specialized metabolism – being targets for manipulation for improving agronomic traits. Protein content is a complex trait that involves many genes, possibly including amino acid transporters. In addition, the amount of nitrogen needed by and available to the plant increases or decreases depending on the environment conditions. How plants control nitrogen need and use at the molecular level is not well understood. The data presented here challenge a current model and I report how a protein (AAP1) involved in the acquisition of amino acids from the soil provides regulatory control over these processes. . This valuable information is useful for better understanding how plants use nitrogen and more precise breeding methods can be used to improve traits, such as protein content in agronomically important crops.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/113288 |
| Date | 28 July 2021 |
| Creators | Shelley, Brett A. |
| Contributors | Plant Pathology, Physiology and Weed Science, Pilot, Guillaume, Beers, Eric P., Winkel, Brenda S. J., Jelesko, John G. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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