UC San Diego

Heavy metals and metalloids are a prominent threat to human health worldwide. Unfortunately, plants expose people to heavy metals and metalloids through diet. To develop plants capable of protecting people from heavy metal and metalloid exposure, the molecular systems of plants in their response to heavy metals and metalloids must be elucidated. In the first chapter of this study, a luciferase reporter construct containing a promotor region for the SULTR1;2 gene was inserted into Arabidopsis thaliana lines. These lines were then mutated with Ethane methosulfornate (EMS), and a forward genetic screen was conducted that searched for shifts in luciferase luminescence in response to cadmium. In these screens, 3 types of classes of shifts in luminescence were procured from the mutant lines, and were classified as having a constitutive (crc1), super (src1), or non-response (nrc1, 2) to cadmium. The nrc1, 2 mutants have since been characterized. Using bulk-segregation analysis, mutated genomic regions that separated with the src1 and crc1 luciferase phenotypes were determined. In addition, the crc1 mutants expressed a root-growth phenotype in sulfur- free media supplemented with cadmium and selenium. Src1 mutants showed a greater SULTR 1;2 expression in response to cadmium. T-DNA knockout lines for all candidate genes were ordered, genotyped, and propagated, and were used to determine potential causative genes for the src1 and crc1 phenotypes. In the second chapter, inductively-coupled electron optical electron spectroscopy was conducted to determine the heavy metal and arsenic concentrations of edible crop tissues grown in Campus Community Gardens around UCSD.