阿拉伯芥 B-box 第五群蛋白-BBX29 及 BBX30 調控開花之研究

Abstract

在植物中，複雜網絡調控開花是為了確保能在適當的時間完成花朵的發育。開花有賴環境的訊息如：光線、溫度，以及內在基因途徑去調控。光線能引發生物時鐘的變化去調控開花，其中CIRCADIAN CLOCK ASSOCIATED 1 (CCA1)、 LATE ELONGATED HYPOCOTYL (LHY)及Timing of CAB Expression 1 (TOC1)等蛋白，扮演著震幅調控機制者，其中CCA1及LHY的高峰表現在清晨，功能被認為是清晨時期的調控者。 GIGANTEA (GI) 扮演著生物時鐘傳導訊息的整合者角色，使光週期的基因表現，包括：最主要的調控蛋白-- CONSTANS (CO)及FLOWERING LOCUS T (FT)，可調控阿拉芥長日照的開花。然而CO的轉錄及轉譯後調控，是為了確保FT轉錄表現得以精準的調節。B-box蛋白帶有b-box結構域，或有無CCT結構域，扮演著特有角色於調控CO。B-box第五群蛋白包括有BBX26到BBX32，結構只具有一個b-box結構域而無CCT結構域，扮演著更多調控角色。大量表現BBX29基因下，會導致阿拉伯芥在長日照與短日照環境下晚開花；相較於bbx29突變株，在長日照情況下會表現早開花之性狀。經基因分析，CO的轉錄沒有受影響之下，下游基因FT及SOC1的表現則被顯著壓制。相對於bbx29突變株則FT轉錄有著上調控的表現。此外，在基因大量表現組中，開花抑制基因FLC則呈現上調控之情形。BBX29與CO兩種蛋白具有相互結合作用，這似乎影響CO在細胞核的分佈情形。這樣的發現可以闡述BBX29調控開花是藉由與CO的結合作用及FLC的誘導有關。雖然BBX30不具有影響FLC的功能，但大量表現BBX30基因的結果，會造成晚開花的性狀與BBX29調控開花相似。這兩個基因表現之生理節律都是於ZT4有個高峰值。在CCA1及LHY基因突變狀況之下，BBX30基因的生理節律表現，會被改變於高峰時間與擺盪震幅。於此可證，BBX30基因乃受生理時鐘調控。至此，本研究提供了BBX29及BBX30在開花調控上更深入的研究探討。

Complex networks regulate flowering to ensure the suitable timing for floral development in plants. Flowering depends on environmental cues like light, temperature, and internal genetic pathways. Light can trigger the oscillator of the circadian clock to regulate flowering. The central oscillator is controlled by CCA1 (CIRCADIAN CLOCK ASSOCIATED 1), LHY (LATE ELONGATED HYPOCOTYL), and TOC1 (Timing of CAB Expression 1), where CCA1 and LHY levels peak at dawn and function as morning-phased regulators. GI (GIGANTEA) plays an integrator role in transducing the clock signaling to induce the expression of photoperiodic genes, including the pivotal components, CONSTANS (CO) and FLOWERING LOCUS T (FT), to control long-day flowering in Arabidopsis. Transcriptional and post-translational regulations ensure that CO can precisely regulate FT expression. B-box proteins containing b-box domains with or without a CCT domain play significant roles in regulating CO. Group V B-box proteins (BBX26 to BBX32) possessing only one B-box domain and lacking a CCT domain may also have roles in the regulation. BBX29 overexpression resulted in late-flowering under both long-day and short-day conditions. In contrast, the bbx29 mutants showed an early-flowering phenotype under long-day conditions. The transcript abundance of CO was not affected, but the expression of its downstream genes, FT and SOC1, was significantly suppressed in the overexpression lines. Consistently, the FT transcript level was up-regulated in the bbx29 mutants. The gene encoding the flowering repressor FLC was also up-regulated in the overexpression lines. BBX29 can interact with CO, which seems to alter the CO distribution in the nucleus. Our findings suggest that BBX29 may regulate flowering by interacting with CO and FLC induction. Although BBX30 did not affect FLC expression, overexpression of BBX30 delayed flowering through a regulatory mechanism similar to BBX29. Both genes showed a rhythmic expression pattern with their expression peak at ZT4. Mutations in CCA1 and LHY influenced BBX30 expression in relative amplitude and peak time, suggesting that BBX30 may be regulated by circadian rhythm. Here, I provide insights on BBX29 and BBX30 in flowering regulations.