日夜週期環境中阿拉伯芥調控BPC3的作用機制研究

A mechanistic study on the regulation of BPC3 in Arabidopsis under day-night cycles

李宜臻(Yi-Chen Lee)

指導教授 ： 蔡皇龍

國立臺灣大學/生命科學院/分子與細胞生物學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202101453

摘要

BASIC PENTACYSTEINE (BPC) 家族成員為植物特有的GAGA結合轉錄因子，負責徵召染色質修飾複合體並抑制基因表現。已知BPC成員之功能間兼具重疊及拮抗情形，其中BPC3受其他BPC成員的共同拮抗。實驗室先前研究發現BPC3在過量表現時會同時抑制阿拉伯芥生理時鐘以及自主開花調控途徑之多個核心基因，阻礙植物生長與發育甚至死亡，顯示精準調控BPC3表現為植物不可或缺的生存要件。為了解BPC3轉錄的調控機制，我檢測BPC3 在不同bpc突變組合下的表現，發現BPC3 表現隨BPC基因數量減少而提高，並有自我回饋抑制現象，顯示BPCs成員間的拮抗的確涉及轉錄抑制。根據DNA affinity purification -seq資料庫可知參與異染色質靜默的轉錄因子AT-RICH INTERACTION DOMAIN3 (ARID3)能結合BPC3啟動子，我誘導ARID3過量表現後，發現BPC3啟動子活性會被即時抑制，顯示BPC3為受ARID3調控之標的基因，實驗結果符合ARID3對轉錄的負向功能。然而在arid3突變株中，包括BPC3與其他已知ARID異染色質標的區域表現量卻是降低的，顯示arid3突變株中可能有功能補償或基因迴路失衡的現象。本研究揭示了BPC與ARID兩種負向調控機制同時參與了BPC3的轉錄調控，阿拉伯芥藉由多重轉錄抑制確保BPC3表現量能夠被精確控制。

關鍵字

GAGA結合因子 ； 轉錄調控 ； 阿拉伯芥 ； BASIC PENTACYSTEINE (BPC) ； AT-RICH INTERACTION DOMAIN (ARID)

並列摘要

BASIC PENTACYSTEINE (BPC) family members are GAGA-binding transcriptional repressors for recruiting chromatin modification complexes in plants. The overlapping and antagonistic functions among BPC members have been revealed that BPC3 is simultaneously antagonized by other BPCs. Our previous study showed that ectopic BPC3 expression suppresses multiple core genes of circadian clock and autonomous flowering controls, consequently impedes the plant development or even leads to death. Therefore, a precise regulation of BPC3 expression is crucial for plant survival. To unravel such regulatory mechanism, I profiled BPC3 expression in different bpc mutant combinations. The expression of BPC3 was increased with the decrease of BPC gene number, in addition, an auto inhibition of BPC3 transcription was observed, indicating that the antagonistic function among BPCs has involved in the transcriptional inhibition. Furthermore, the public DNA affinity purification-seq (DAP-seq) database shows that a component of heterochromatin silencer, AT-RICH INTERACTION DOMAIN 3 (ARID3), binds to BPC3 promoter. I then found that the induction of ARID3 overexpression instantly repressed BPC3 promoter activity, indicating that BPC3 was a target suppressed by ARID3. Nevertheless, transcript levels of BPC3 and other known ARID-targeted heterochromatin regions were increased in the arid3 mutant, suggesting that a functional compensation or gene loop imbalance might occur in the mutant. My study revealed that two inhibitory mechanisms, BPC and ARID, have constituted an accurate suppression on BPC3 in Arabidopsis.

並列關鍵字

GAGA-binding factor ； transcriptional regulation ； Arabidopsis ； BASIC PENTACYSTEINE (BPC) ； AT-RICH INTERACTION DOMAIN (ARID)

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