Doctor of Philosophy
Date of Defense
Bethany K. Zolman, Ph.D.
James S. Chickos, Ph. D.
Plant peroxisomes function in fatty acid β-oxidation, jasmonic acid (JA) synthesis, and conversion of indole-3-butyric acid (IBA) to indole-3-acetic acid (IAA). Peroxisomes lack genetic material; proteins required for peroxisomal processes are imported posttranslationally. The PEX5 and PEX7 receptors import proteins containing one of two peroxisomal targeting signals (PTS1 or PTS2). I took a genetic approach to better understand protein import and to elucidate the role of Acyl-CoA Oxidase (ACX) enzymes in the model plant Arabidopsis thaliana. ACX enzymes catalyze the first step in β-oxidation. There are six ACX genes in Arabidopsis and each ACX enzyme acts on specific chain-length targets, but in a partially overlapping manner. To elucidate the substrate specificity of ACX enzymes and examine their roles in planta, I generated higher order acx mutants. ACX gene expression studies show distinct patterns between Col-0 and Ws and the enzymes showed altered activity during development. acx triple mutants showed reduced seed-storage mobilization and resistance to IBA. Several mutants specifically showed reduced fertility and the acx1acx3acx5 defect was rescued with JA. Analysis of the higher order acx mutants has allowed me to determine which ACXs act in specific peroxisomal β-oxidation pathways. To elucidate the mechanism of peroxisome matrix protein import, I studied an insertion mutant in the PEX5 receptor. This mutant, designated pex5-10, makes a truncated pex5 protein, has germination defects and is dependent on sucrose for establishment. PTS1 and PTS2 protein import and enzymatic processes are also disrupted. To specifically study PTS1 protein import, I created a pex5 mutant lacking the PTS1 binding region. This mutant rescued the PTS2 import defects in pex5-10. The pex5-10 and PTS2 rescued lines allowed me to separate specific processes affected by import of PTS1 or PTS2 proteins. This study has contributed to our understanding of the differences in the ACX genes and proteins in different Arabidopsis accessions and the role each protein plays in peroxisomal processes. The study also provides a better understanding of PTS1 and PTS2 proteins in specific peroxisomal pathways. Together these studies will contribute to elucidating the mechanism for the requirement for peroxisomal processes in plant growth and development.
Khan, Bibi Rafeiza, "Elucidating matrix protein import and beta-oxidation pathways in plant peroxisomes" (2011). Dissertations. 391.