Protein targeting and import into plant peroxisomes

A main characteristic of the eucaryotic cell is the compartmentalization of different metabolic processes into membrane-enclosed organelles. Each organelle contains a characteristic set of proteins to accomplish specific metabolic functions that are often essential for the cell's viability. The most recently discovered class of organelles includes the microbodies that encompass a group of organelles which have some morphological properties in common. Microbodies are ubiquitous in eucaryotic cells and can be subdivided into different types of organelles according to their metabolic functions (e.g. peroxisomes and glyoxysomes). The size and number of microbodies per cell is often related to the developmental stage and/or the organism in which they occur. This implies that microbody proliferation is inductible in nature. This review summarizes the progress made in recent years in understanding how proteins are targeted to and imported into microbodies. Major breakthroughs were the identification of the two main peroxisomal protein targeting signals (PTS1 and PTS2), protein receptors for the signals and the isolation of yeast mutants defective in the biogenesis of microbodies. Especially the availability of these mutants has opened new ways to identify proteins involved in microbody protein import in plants as well as animals.