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内容記述 |
Peroxisomes in higher plant cells have been recognized to differentiate into at least three different classes, namely glyoxysomes, leaf peroxisomes and unspecialized peroxisomes. Glyoxysomes are present in cells of storage organs, such as cotyledons during post-germinative growth of oil seed plants, as well as in senescent organs. They contain enzymes for b-oxidation and the glyoxylate cycle to degrade fatty acids. In contrast, leaf peroxisomes are found widely in cells of photosynthetic organs. They play a role of glycolate metabolism in photorespiration pathway. Other organs, such as roots and stems, contain unspecialized peroxisomes whose function is still obscure. Those differentiated peroxisomes are known to convert into one another under certain conditions. For example, glyoxysomes in etiolated cotyledons are transformed directly into leaf peroxisomes during the greening of cotyledons. Recent progresses on the analyses of Arabidopsis mutants suggest that plant peroxisomes have more diverse functions than we know at present.<br /> In chapter 1, to reveal genetic configuration of plant peroxisomes, she comprehensively surveyed genes related peroxisomal function and biogenesis in the entire Arabidopsis genome sequence. In this survey, she used amino acid sequences that are well known as targeting signals of peroxisomal matrix proteins, namely PTS1 and PTS2. She identified 256 gene candidates of PTS1- and PTS2-containing proteins. In addition to the 256 gene candidates, she put in another 30 genes of non-PTS-containing proteins predicted to relate peroxisomal function and biogenesis, such as peroxisomal membrane proteins. Of these, only 29 proteins have been reported to be functionally characterized as peroxisomal proteins in higher plants. Using the total 286 peroxisomal genes, she extensively investigated expression profiles in various organs of Arabidopsis to reveal diversity of plant peroxisomes. Statistical analyses of these expression profiles revealed that peroxisomal genes could be divided into five groups. One group showed ubiquitous expression in all organs examined, while the other four were classified as showing organ-specific expression in seedlings, cotyledons, roots and in both cotyledons and leaves. These data proposed more detailed description of differentiation of plant peroxisomes.<br /> The aims of chapter 2 are to reveal gene expression profiles during functional transition of plant peroxisomes and to investigate candidate genes functioned at the process. She compared gene expression profiles of cotyledons illuminated for 2hr, 6hr, l2hr and 24hr in white light following 4 days growth in dark with cotyledons grown for 4 days in dark. During illumination, the genes of enzymes for b-oxidation and glyoxylate cycle were reduced. On the other hand, genes of enzymes for phtorespiration were induced by light. Along with these genes, a lot of peroxisomal genes changed their expression levels during irradiation. In contrast, nine peroxisomal genes showed transitory expressed pattern during illumination. It was suggested that the genes functioned at the process of functional transition of peroxisomes.<br /> In this study, she revealed the diversity of plant peroxisomes and declared gene expression profiles during the functional transition of peroxisomes. This study will serve as a foundation for revealing unidentified peroxisomal functions in plant cells. |
要旨・審査要旨 / Abstract, Screening Result (235.3 kB)
