阿拉伯芥第二類和第四類組蛋白去乙酰化酶功能分析

Functional studies of class II and IV histone deacetylases in Arabidopsis

瑪洛娜(Malona Velasco Alinsug)

指導教授 ： 吳克強

國立臺灣大學/生命科學院/植物科學研究所/博士(2010年)

https://doi.org/10.6342/NTU.2010.03018

摘要

組蛋白乙醯化作用可誘導染色質結構的開放，從而促進基因轉錄；去乙醯化使染色質結構緊密，從而抑制基因轉錄。在植物中，12個組蛋白去乙醯酶屬於RPD3/HDA1家族，它們被進一步被化分成獨特的3類，分別為Class I、Class II及Class IV。在這12個HDAs中，4個尚未被歸類的為HDA8、HDA10、HDA14及HDA17。根據我們對組蛋白去乙醯酶保守區域作演化樹的分析，HAD10和HDA17在序列上與Class I具有高度的同源性，而HDA8和HDA14與Class II的HDA5、HDA15及HDA18具有高度的相似性。
　　在人類及其他模式生物中，Class II組蛋白去乙醯酶具有胞核間的穿梭的功能。這一特有的功能性調控機制，除了植物外在其他動物體中己被研究。在本研究中，我們證實了Class II及IV的HDAs定位在細胞質及細胞核裡。HDA15在光照下特異定位在核仁裡；而經由黑暗處理後，則定位於細胞質中。這一結果證明真核生物的Class II組蛋白去乙醯酶具有胞核之間穿梭的特性。
目前關於植物Class II及Class IV組蛋白去乙醯酶，除了發現HDA18扮演根表皮形態發育的角色外，並無其他的研究。本研究通過對T-DNA突變、RNAi及過量表現基因的轉殖株的功能性分析，HDA2及HDA15在光形態發育中扮演正向調控因子的角色，並抑制PIFs和COP1的表現。這一發現進一步揭示了組蛋白修飾在光照下調控基因表現的作用。光不只促進在光形態中起主要作用的正向調控因子的乙醯化，並且也可能同時利用去乙醯化作用抑制 COP1和PIFs活性。在光訊息傳遞中，組蛋白的乙醯轉移酶與去乙醯酶的作用可能形成一個重要轉錄調控的開關。

關鍵字

組蛋白去乙醯基酵素 ； 核質間穿梭 ； 光形態發生

並列摘要

Histone acetylation has been known to induce an open chromatin configuration leading to gene transcription while deacetylation stimulates chromatin condensation triggering transcriptional quiescence. In Arabidopsis, there are 12 histone deacetylases classified under the RPD3/HDA1 superfamily which is further subdivided into 3 distinct classes namely Class I, II, and IV. Among these 12 HDAs, 4 remains to be unclassified namely HDA8, HDA10, HDA14, and HDA17. Based on our phylogenetic analyses, HDA10 and HDA17 share high sequence homology to members of the Class I HDAs while HDA8 and HDA14 exhibited higher similarity with HDA5, HDA15, and HDA18, members of the Class II HDAs, based on their conserved histone deacetylase domains.
Moreover, Class II histone deacetylases in humans and other model organisms undergo nucleocytoplasmic shuttling. This unique functional regulatory mechanism has been well studied especially in mammalian organisms except in plant systems. In this study, we have paved the baseline evidence for the cytoplasmic and partial nuclear localization of Class II & IV HDAs. HDA15, in particular, localizes in the nucleolus in the presence of light and eventually transports into the cytoplasm upon dark treatment. This data provides the final piece of the puzzle concluding that nucleocytoplasmic shuttling, indeed, is a hallmark for all eukaryotic Class II histone deacetylases.
Except for HDA18 which plays a role in root epidermal patterning, there are no other studies elaborating on any of the repressive functions of Class II & IV histone deacetylases in plants. Based on the functional genetic analyses of HDA2 and HDA15 using T-DNA knock out, RNAi, and overexpression plants, HDA2 and HDA15 play positive regulatory roles in photomorphogenesis repressing the expression of PIFs and COP1. The findings of this research fine tune our prior understanding of the role of histone modifications in light-regulated gene expression such that light not only induces the acetylation of key positive regulators of photomorphogenesis but also may render the simultaneous repression and inactivation of COP1 and PIFs via deacetylation. This concerted enzymatic activity of histone acetyltransferases and deacetylases in the light signaling pathway may take a colossal hold on the master switches controlling its transcriptional regulation.

並列關鍵字

histone deacetylase ； nucleocytoplasmic shuttling ； photomorphogenesis

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