UC San Diego

In Arabidopsis thaliana, cadmium, a non-essential toxic heavy metal, induces transcription of many genes, including a cadmium-inducible sulfate-transporter, SULTR1;2. The mechanism of cadmium-induced gene expression remains unknown. In research by Jobe et. al. (2012), pSULTR1;2 was fused to a firefly luciferase reporter gene, the resulting seeds mutagenized with ethyl methanesulfonate (EMS). A forward genetic screen for altered responses to cadmium was conducted and lines were categorized by their novel phenotypes. Those addressed in this thesis are crc1 (Constitutive Response to Cadmium) and src1 (Super Response to Cadmium). The exact location of the causative mutations of crc1 and src1 remains unknown, but rough mapping using bulk segregant analyses suggest the mutations are in chromosome four. We ordered T-DNA insertion mutant lines generated by Salk Institute, containing gene knockouts in this mapping region. Of the ordered T-DNA mutant lines, 8 homozygous lines were isolated, 12 heterozygous lines were verified, and insertions were not confirmed in 22 lines. The Salk lines investigated in this thesis are SALK_021343, with exonic insertions in opposite, overlapping DNA strands disrupting a peroxidase gene and a thionin family pseudogene; and SALK_061827, with an exonic insertion and intronic insertion in the same thionin family pseudogene and peroxidase gene, respectively. We evaluated cadmium accumulation and SULTR1;2 induction in cadmium-exposed seedlings; both Salk lines ran against wildtype, crc1, and src1 when able to, aiming to locate the causative genes in crc1 and src1. Our data suggest preliminary putative exclusion of SALK_021343 and SALK_061827 candidacy as the causative mutated genes in src1.