| Summary: | 碩士 === 國立臺灣師範大學 === 生命科學系 === 104 === Toc159 is the main receptor for import of nuclear-encoded plastid proteins. Based on sequence homology and substrate specificity, four Arabidopsis Toc159 homologues are classified to two subgroups, atToc159/atToc90 and atToc132/atToc120. In order to verify the particular expression pattern of these family members, GUS activity of transgenic plants expressing GUS coding sequence driven by different lengths of the upstream regulatory sequences of atTOC159/atTOC132/atTOC120/atTOC90 were analyzed. Our data suggest that all atTOC159 genes consistently express in roots and stipules. Nevertheless, diverse expression patterns are observed in other above-ground tissues. Except for atTOC120, the rest of three genes are expressed in mesophyll cells of cotyledons and leaves, and specialized epidermal cells such as guard cells and trichomes. AtTOC159, atTOC132 and atTOC90 also express in reproductive tissues such as styles, and vascular bundles of sepals and anther filaments. Intriguingly, atTOC120 is uniquely expressed in pollen grains. The expression yield of atTOC120 and atTOC90 can be significantly up-regulated by their corresponding 5ꞌ untranslated region (5ꞌ UTR) and leader intron sequences. These results conclude that the expression of atTOC159 family members have tissue-type and even cell-type specificity. However, they also express redundantly to secure the normal development of plastids.
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