葉綠體外膜蛋白Toc159是辨識由細胞核解碼合成之色質體(plastid)蛋白的主要受體。根據序列相似性以及對受質的專一性，可將阿拉伯芥4個Toc159的同源蛋白分為兩個次群：atToc159/atToc90及atToc132/atToc120。本研究藉由不同長度atTOC159家族的基因上游調節序列片段黏合至GUS報導基因的轉殖植株，進行atTOC159家族各成員在組織專一性表現的相關研究。依據研究結果，atTOC159家族基因皆會表現在根及托葉。在其他地上部營養組織，atTOC159、atTOC132和atTOC90在子葉與真葉的葉肉組織，以及特化的表皮細胞，包括保衛細胞、毛狀體(trichome)皆有表現。在生殖組織，atTOC159、atTOC132和atTOC90主要表現在花柱、花萼與花絲的維管束，而atTOC120只在花粉粒表現。除此之外，atTOC120和atTOC90表現量會受到上游5ꞌ端非轉錄區以及領導內插子的促進。總和以上結果，atTOC159家族成員各有不同的組織甚至是細胞專一性，但也相互合作以維持色質體的正常發育。

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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