Using forward genetics to identify novel Arabidopsis thaliana peroxisomal mutants
Doctor of Philosophy
Peroxisomes are single-membrane-bound organelles responsible for key metabolic reactions needed for the development of many eukaryotes. Peroxisomes lack DNA and must import nuclear-encoded proteins from the cytosol. Genetic screens have identified multiple peroxin (PEX) proteins involved in peroxisome biogenesis and import of peroxisomal matrix and membrane-bound proteins. Most proteins are imported into the peroxisome matrix via an incompletely understood process that depends on one of two peroxisome-targeting signals (PTSs), PTS1 and PTS2. In plants and mammals, the N-terminal PTS2 is cleaved after peroxisomal import resulting in a mature form of the protein. In the model plant Arabidopsis thaliana, peroxisomes are the site of β-oxidation of indole-3-butyric acid (IBA) to the active auxin indole-3-acetic acid (IAA). Screens for IBA resistance have confirmed the identity of several PEX proteins in Arabidopsis. Because peroxisomes are also the site of fatty acid β-oxidation in plants, many IBA-resistant pex mutants display sucrose-dependent growth following germination. Here I describe the optimization of genetic screens to isolate, identify, and characterize peroxisomal proteins that allow plants to develop without sucrose supplementation, respond normally to IBA, and efficiently process PTS2 proteins. I describe the characterization of novel mutants of pex6, pex12, pex13, and pex26 isolated from this screening. These mutants help to provide us a better understanding of peroxisome biogenesis and receptor recycling.