Studies on novel functions of plant peroxisomes

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1) Almost all of the peroxisomal matrix proteins are known to contain one of two targeting signals(PTS1 and PTS2) within the molecules. We identified 256 gene candidates of PTS1- and PTS2- containing proteins and another 30 genes of non-PTS-containing proteins from Arabidopsis genome. Custom-made DNA microarray covering all these genes was used to investigate expression profiles of the peroxisomal genes in various organs.2) Bioinfomatic analysis of Arabidopsis genome predicted the presence of 15kinds of genes, called PEX genes, for peroxisomal biogenesis factors. We comprehensively investigated whether or not these predicted PEX genes function in peroxisome biogenesis by generating knock-down mutants that suppress PEX gene expression by RNA-interference. Phenotypes of these mutants allowed us to identify the functional PEX genes, which can be classified into two groups, i.e. PEX genes regulating for peroxisomal morphology and PEX genes regulating for peroxisomal protein import.3) To clarify the function of root peroxisomes, we characterized a peroxisomal polyamine oxidase, AtPAO4 gene that is expressed in roots of Arabidopsis thaliana. This indicates that root peroxisomes are involved in polyamine metabolism.4) We also made a two-dimensional protein map of glyoxysomes isolated from soybean. Peptide MS fingerprinting analyses allowed us to identify novel proteins existing in either glyoxysomes. Some of these proteins contain no obvious PTS1 and PTS2. Combination of the transcriptomic and proteomic analyses is providing us with a new insight into plant peroxisomal functions.