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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Plant Biology

Year Degree Awarded

2018

Month Degree Awarded

September

First Advisor

Elsbeth L. Walker

Subject Categories

Life Sciences | Plant Biology | Plant Sciences

Abstract

Iron-deficiency anemia is one of the most prevalent forms of malnutrition worldwide, affecting 1.62 billion people, with the population in developing countries being the most affected. Iron is equally vital in plants to perform essential functions such as photosynthesis. Crop grasses form part of everyday human nutrition, contribute fundamentally to human caloric intake, and, in some parts of the world, are the primary source of food. Grasses acquire iron from the soil by secreting chelator molecules called phytosiderophores to solubilize iron, making it available to be transported by the Yellow Stripe1 (YS1) transporter.

In this dissertation, I studied aspects of primary iron uptake: specifically the mechanism of phytosiderophores secretion in the model grass Brachypodium distachyon and the staple crop Zea mays. I characterized brachypodium TOM1 transporters to uncover how phytosiderophores are released to the soil. I generated transgenic brachypodium plants over-expressing the Transporter of Mugineic Acid fused with Green Fluorescence Protein (BdTOM1-GFP) to analyze phenotypes of BdTOM1 overexpression and the localization of the BdTOM1 protein. I evaluated the effect of iron status on BdTOM1 transporter expression showing that BdTOM1 expression is up-regulated during iron deficiency in both shoots and roots. The expression of BdTOM1 did not follow a diurnal regulation pattern as phytosiderophores secretion in brachypodium. Unfortunately, the transgenic lines generated were not optimal for analyzing phenotype and characterizing BdTOM1 function

Another aim of this dissertation was to identify the underlying mutant gene causing the yellow stripe 3 (ys3) phenotype in maize. Multiple lines carrying ys3 alleles were analyzed at the ZmTOM1 locus, and deleterious mutations were found in each ys3 allele. These results bring closure to the quest for the transporter responsible for phytosiderophores secretion and complete the final piece in the primary iron uptake model. Additionally, 32 previously uncharacterized yellow-striped mutants from the Maize Genetics Cooperation Stock Center were screened by performing complementation tests with the maize mutants ys1 and ys3. These experiments led to the identification of novel maize yellow-striped ys* mutants, and further analysis revealed that low iron content in leaves caused the chlorotic (yellow-striped) phenotype. Complementation tests among the ys* mutants showed that they are not allelic, and each one represents a novel locus contributing to iron deficiency chlorosis in maize. The characterization and cloning of ys* genes could expand our knowledge of the grass-specific machinery for iron acquisition.

Included in

Plant Biology Commons

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