UC San Diego

Consumption of food crops with heavy metal and metalloid content may be associated with harmful health risks. After exposure to heavy metals, plants induce significant gene expression changes, but the mechanisms underlying this transcriptional response are unknown. Forward genetic screens for mutants displaying altered heavy metal-induced gene expression were performed to address this issue. Subsequent mapping of the causal genes provides an approach to illuminate the underlying mechanisms. “Luciferase reporter lines” were created by merging the promoter of cadmium-induced SULTR1;2 gene to the bioluminescent firefly luciferase gene within Arabidopsis thaliana (Jobe et al., 2012). Mutant groups were created by subjecting “luciferase reporter lines” to ethyl methanesulfonate (Jobe et al., 2012). Forward genetic luciferase screens of mutagenized lines showed a phenotypic response when exposed to cadmium. Three mutant subgroups were defined as “constitutive response to cadmium (crc1)”, “super response to cadmium (src1)”, and “non-response & reduced response to cadmium (nrc1,2 were characterized)” (Jobe et al., 2012). Evaluation of bulk segregation analysis led to the rough mapping of the cadmium-induced luciferase luminescence mutants crc1 and src1. Genes in candidate regions were mapped, and their respective T-DNA insertion lines were ordered. ICP-OES studies displayed no significant distinction in cadmium accumulation between wild-type, crc1, and src1 mutants. Using RT-qPCR, src1 mutants and candidate T-DNA insertion lines displayed similar transcriptional gene expression responses to cadmium. These results may expand our knowledge of plant genes involved in the heavy metal response.