Peroxisomes are organelles originating from the endoplasmic reticulum. Peroxisome biogenesis requires multiple peroxins, including PEX19, a prenylated protein that helps deliver peroxisomal membrane proteins in yeast and mammals. Arabidopsis thaliana PEX19 is encoded by two isogenes, PEX19A and PEX19B. I demonstrate that pex19A and pex19B insertional mutants lack obvious abberant physiological phenotypes. I provide evidence that pex19A pex19B double mutants are inviable, that PEX19B is more abundant than PEX19A in young seedlings, that Arabidopsis PEX19 is farnesylated in vivo, and that YFP-PEX19 predominantly associates with what appears to be a subcellular membrane regardless of its prenylation state. I show that farnesyltransferase mutants apparently contain only non-prenylated PEX19 and lack phenotypes that would indicate inefficient peroxisome activity. My analysis of PEX19 suggests that PEX19 prenylation is dispensable for peroxisome biogenesis, and has generated tools for future studies of the earliest steps in peroxisome biogenesis in plants.

Peroxisomes and mitochondria play a key role in oxygen metabolism. It was widely accepted that the evolutionary adaptation of eukaryotes to anaerobiosis is reflected by the metabolic reduction of mitochondria, and concomitant loss of peroxisomes. The anaerobic protists Mastigamoeba balamuthi (Mb), Pelomyxa schiedti (Ps), and Entamoeba histolytica (Eh) contradict this paradigm. They possess anaerobic types of mitochondria (hydrogenosomes, mitosomes) but also host "anaerobic peroxisomes". Mb/Ps peroxisomes contain a common set of 13 peroxins (Pexs) that retain the core members of each functional category including components of both PTS1 and PTS2 machinery for matrix protein import. However, Eh peroxisomes harbour a reduced set of 7 known Pexs and lacks several components that are highly conserved among most eukaryotic lineages, including components of PTS2 machinery (Pex7), the RING complex (Pex2/10/12), docking complex (Pex13), and peroxisomal membrane protein import receptor (Pex3). Concerning the functional annotation, no clear biochemical context has been found in these anaerobic peroxisomes. They are diverse in enzymatic contents and are involved in various metabolic reactions, while catalase and typical peroxisomal enzymes of fatty acid beta-oxidation are absent. Mb peroxisomes appear to be involved in...

Peroxisomes compartmentalize a variety of important metabolic reactions including fatty acid β-oxidation and the related process of IBA β-oxidation. Peroxisomal proteins are encoded by nuclear genes and must be post-translationally imported. A dynamic import process is vital for proper matrix protein localization and is dependent on the family of peroxin (PEX) proteins. The delivery and peroxisomal import of cargo from a loaded receptor, PEX5 or PEX7, is carried out by the early-acting peroxins, including PEX13 and PEX14, and receptor recycling is carried out by the late-acting peroxins, including PEX4 and PEX6. In this thesis, I describe the use of double mutant analysis to differentiate early-acting and late-acting pex mutants by phenotypic and molecular analysis. I found that double mutants made with two early-acting or two late-acting pex mutants showed enhanced phenotypes in β-oxidation and import defects. In contrast, defects of double mutants made with a weak early-acting mutant and a late-acting mutant were suppressed. Additionally, I found that receptor localization is central to proper peroxisomal function. My results suggest that when the receptor is not removed from the peroxisome, stabilized peroxisomal pores may be formed, perhaps impairing peroxisomal function due to leaching of peroxisomal contents. Together my data suggest that balance between import and receptor recycling is fundamental for peroxisomal function. In humans, peroxisomal biogenesis disorders are most often caused by defects in late-acting peroxins. Peroxisomal defects occur in plants and humans as a result of the same lesions in PEX proteins. The understanding of how these late-acting defects can be ameliorated in plants, may inspire new approaches to human therapeutics.

京都大学 / 新制・論文博士 / 博士(農学) / 乙第13458号 / 論農博第2899号 / 新制||農||1088(附属図書館) / 学位論文||R3||N5362(農学部図書室) / (主査)教授 小川 順, 教授 阪井 康能, 教授 栗原 達夫 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM