| 摘要: | 糖在植物的生長與發育上有多種的角色，除了是能量的來源也是訊號分子。植物中，MYB轉錄因子是一群含有1-4個不完全重複的DNA結合單元，此DNA結合單元大約由50個胺基酸組成且會形成三個阿法-螺旋(α-helices)。MYB家族的轉錄因子可依DNA結合單元中的不完全重複數目可分成四個次家族，R2R3, R1/2, R1R2R3和R1R2R2R1。先前，我們實驗室發現了水稻中三個屬於R1/2種次家族的OsMYBSs，參與糖調控α-澱粉水解酶(α-amylase)基因表現的機轉途徑中。為了更進一步探討阿拉伯芥中AtMYBSs的生物角色，我們利用水稻OsMYBS1的蛋白質胺基酸序列，找出阿拉伯芥中兩個胺基酸序列相似的MYBS蛋白質，分別命名為AtMYBS1和AtMYBS2。水稻胚的短暫表現分析中說明了AtMYBS1和AtMYBS2可以結合糖類反應序列，且會促進含糖反應序列的啟動子活性。我們發現了atmybs1突變株是對於高濃度葡萄糖和ABA是過度敏感的，而atmybs2突變株則呈現不敏感的外表型。另外AtMYBS1和AtMYBS2是參與控制葡萄糖反應相關基因的表現，當AtMYBS1突變後顯示了增強HXK1、CAB1、APL3和CHS等基因的表現，確定AtMYBSs在阿拉伯芥中參與糖感應的調控機制。atmybs1突變株在葡萄糖處理時加入ABA生合成抑制劑，Fluridone，可以部分回復糖類所引起的生長遲緩。而且，在atmybs1突變株中，四個ABA生合成基因與兩個ABA訊號基因表現均高於野生型植株。相反的，atmybs2突變株中HXK1、CAB1、APL3和CHS等基因的表現量降低，而且ABA相關基因表現量也降低，這些結果說明了AtMYBS1和AtMYBS2在葡萄糖調控早期幼苗生長發育過程中扮演相反的角色，而此過程需經ABA。; Sugars can be as energy sources and signaling molecules in plant growth and development. In plant, MYB transcription factor is a family that composed 1–4 imperfect DNA-binding domains (DBD). Each repeat of DBD contains approximately 50 amino acids in length and forms to 3 α-helices. Base on copy number of DBD, MYB transcription factors have been group into four types, R2R3, R1/2, R1R2R3, and R1R2R2R1/2. Previously, our lab has demonstrated that R1/2 type OsMYBSs are involved in sugar- and hormone-regulated α-amylase gene expression mechanism in rice. To further investigate the biological roles of AtMYBSs protein in Arabidopsis, we identified two OsMYBS1 homologous genes,AtMYBS1 and AtMYBS2, in Arabidopsis. Rice embryo transient expression assays indicated that both AtMYBS1 and AtMYBS2 was able to bind sugar response element (TATCCA)to activated sugar response element containing promoter. The atmybs1mutant confers hypersensitivity to glucose and ABA, whereas atmybs2 mutant exhibited hyposensitivity to those treatments. Moreover, AtMYBS1 and AtMYBS2 are involved in the control of Glc-response gene expression, as the atmybs1 mutant displays increased expression of hexokinases dependent (HXK1), photosynthetic (CAB1), starch synthesis (APL3) and anthocyanin biosynthesis (CHS) gene, whereas atmybs2 mutant exhibited decreased those gene expression, indicating that the AtMYBS1 and AtMYBS2 play a role in sugar sensing in Arabidopsis. In addition, the ABA biosynthesis inhibitor fluridone partially rescues the sugar-mediated growth arresting. Moreover, the mRNA level of four ABA biosynthesis genes and two ABA signaling genes were increased Glc treatedatmybs1 seedlings, whereas decreased in atmybs2 seedlings. These results suggested that, AtMYBS1 and AtMYBS2 play opposite roles in regulated Glc and ABA signaling during early seedling development. |
