DEVELOPING MORE EFFECTIVE IRON BIOFORTIFICATION OF MAIZE BY TARGETED OVEREXPRESSION OF ENDOGENOUS GENES.

Iron deficiency remains one of the most widespread micronutrient deficiencies worldwide. Biofortification of crops through genetic manipulation of iron uptake, transport, and storage pathways offers a promising strategy to combat these deficiencies; however, success has been limited by an incomplete understanding of how iron is distributed into seeds, particularly in grasses such as maize. This dissertation investigates the roles of three conserved iron transporters—ZmYSL1, ZmYSL3, and ZmOPT3—in maize and evaluates how their expression in specific tissues affect kernel iron levels. Using reverse genetics, mutants were identified and characterized to assess functional similarities relative to Arabidopsis orthologs. Targeted overexpression strategies were made to elevate transporter expression in specific tissues involved in long-distance iron transport, maternal nutrient transfer, and filial uptake. Unlike Arabidopsis models, maize ysl1, ysl3, and opt3 mutants did not display severe iron deficiency phenotypes and revealed extensive genetic compensation by paralogous transporters. Emphasizing the differences in maize iron homeostasis and limitations of relying solely on results from model species. Tissue-specific overexpression of ZmYSL1, ZmYSL3, and ZmOPT3 failed to consistently increase kernel iron, zinc, or copper concentrations under field conditions due to transgene silencing. Evaluation of transgenic lines with confirmed stable expression establishes potential mechanisms for how iron is distributed into kernels of transgenic crops and will help inform future biofortification strategies.