阿拉伯芥第一類BPCs調節CYC/TB1家族對花朵對稱性與分枝形成的作用

Abstract

花朵的對稱性影響植物繁衍下一代的效率。已知CYCLOIDEA（CYC）為不同植物物種花朵對稱性的關鍵因子。本論文針對植物特有的GAGA序列結合因子，Class I BASIC PENTACYSTEINE（BPC）基因家族對阿拉伯芥CYC及其同源基因調控機制進行研究。本實驗室過往以大岩桐（Sinningia speciosa）SsCYC 基因上游片段進行酵母菌單雜交(yeast one-hybrid)篩選阿拉伯芥轉錄因子基因庫，結果發現阿拉伯芥之BPC1和BPC2能夠結合於篩選用的核酸片段，顯示BPCs可能調控CYC 基因。於是本論文首先檢測阿拉伯芥bpc突變體的花朵對稱性，發現bpc1-1 bpc2（bpc1,2）和bpc1-1 bpc2 bpc3-1（bpc1,2,3）突變體之花朵由輻射對稱(radial symmetry)轉變成兩側對稱(bilateral symmetry)。進一步測試BPC與SsCYC之阿拉伯芥同源基因TEOSINTE BRANCHED 1-CYCLOIDEA-PCF1 （AtTCP1）之關聯性，發現BPC2和BPC3可抑制，而BPC1則可活化TCP1的轉錄，顯示不同的BPC成員對TCP1的作用有差異。由於bpc突變體亦發生了花序結構的改變，因此也檢測了BPC對於花序分枝調節因子TCP12和TCP18的影響。結果發現BPC1、BPC2和BPC3皆可抑制TCP12，反之卻活化TCP18的轉錄。在bpc突變體中TCP18的下調導致了分枝增加，與其已知抑制花序分枝的作用一致。總結本論文研究發現Class I BPC可藉由調節CYC與其同源基因來調控花朵對稱性和花序分枝的途徑，本研究為花朵對稱性和花序分枝發育的調節機制提供了進一步的分子證據。

Flower symmetry is crucial for the reproductive success. The CYCLOIDEA (CYC) gene has been identified as a critical regulator of floral symmetry across different plant species. In this study, I investigated the involvement of Class I BASIC PENTACYSTEINEs (BPCs), plant-specific GAGA-motif binding factors, in the regulation of CYC and its homologs in Arabidopsis. Based on the results of yeast one-hybrid, we found that BPC1 and BPC2, both members of Class I BPC, can bind to the upstream region of CYC in Sinningia speciosa, indicating a potential role in floral symmetry regulation. I therefore examined the floral symmetry of the bpc mutants and observed a remarkable alternation. Flowers of bpc1-1 bpc2 (bpc1,2) and bpc1-1 bpc2 bpc3-1 (bpc1,2,3) mutants are changed from radial symmetry to bilateral symmetry. This prompted me to relate the BPCs to the SsCYC homolog in Arabidopsis, TEOSINTE BRANCHED 1-CYCLOIDEA-PCF1 (AtTCP1). I demonstrated that BPC2 and BPC3 act as inhibitors, while BPC1 enhances the transcript level of TCP1, indicating that various BPC members modulate TCP1 differently in Arabidopsis. As the bpc mutants showed altered architectures of the inflorescence, the impact of BPCs on TCP12 and TCP18, known regulators of inflorescent branching, was investigated. I found that BPC1, BPC2, and BPC3 repressed TCP12 while activated TCP18. The downregulation of TCP18 in the bpc mutants resulted in a significant increase in the number of branches, consistent with its inhibitory role in the inflorescent branching. In summary, my study provides novel insights into the regulatory mechanisms governing floral symmetry and inflorescent branch development. It highlights the potential role of Class I BPCs in modulating the expression of CYC homologs, as well as their impact on the intricate processes shaping floral symmetry and inflorescent branching in Arabidopsis.