Molecular mechanisms of the microbody transition in higher plants

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In order to clarify the microbody transition in higher plants, we have analyzed the development of microbody membrane proteins and arabidopsis mutants that defects on fatty acid *** -oxidation. We characterized one of the major microbody membrane proteins, PMP38. The deduced amino acid sequence for its cDNA in Arabidopsis thalia na contained polypeptides with 331 amino acids and had high similarity with those of Homo sapiens PMP34 and Candida boidinll PMP47 known as homologues of mitochondrial ATP/ADP carrier protein. Cell fractionation and immunocytochemical analysis using pumpkin cotyledons revealed that PMP38 is localized on microbody membranes as an integralmembrane protein. The amount of PMP38 in pumpkin cotyledons increased and reached the maximum protein level after 6 d in the dark but decreased thereafter. Illumination of the seedlings caused a significant decrease in the amount of the proteinThese results clearly showed that themembrane protein PMP38 in glyoxysomes changes dra … More matically during the transformation of glyoxysomes to leaf peroxisomes, as do the other glyoxysomal enzymes, especially enzymes of the fatty acid *** -oxidation cycle, that are localized in the matrix of glyoxysomes. We previously isolated an Arabidopsis peroxisomedeficient ped2 mutant by its resistance to 2, 4-dichlorophenoxybutyric acid. We describe the isolation of a gene responsible for this deficiency, called the PED2 gene, by positional cloning and confirmed its identity by complementation analysis. The amino acid sequence of the predicted protein product is similar to that of human Pex14p, which is a key component of the microbody protein import machinery. Therefore, we decided to call it AtPex14p. Analyzes of the ped2 mutant revealed that AtPex14p controls intracellular transport of both peroxisome targeting signal (PTS)1 and PTS2-containing proteins into three different types of microbodies, namely glyoxysomes, leaf peroxisomes and unspecialized peroxisomes. Mutation in the PED2 gene results in reduction of enzymes in all of these functionally differentiated microbodies. The reduction in these enzymes induces pleiotropic defects, such as fatty acid degradation, photorespiration and the morphology of microbodies. We also identified PED3 gene as a full-size ATP-binding cassette transporter. The studies on the microbody transition in these mutants are now in progress. Less