TT8 controls its own expression in a feedback regulation involving TTG1 and homologous MYB and bHLH factors, allowing a strong and cell-specific accumulation of flavonoids in Arabidopsis thaliana
TT8 controls its own expression in a feedback regulation involving TTG1 and homologous MYB and bHLH factors, allowing a strong and cell-specific accumulation of flavonoids in Arabidopsis thaliana
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DOI：
10.1111/j.1365-313x.2006.02733.x
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发表时间：
2006-06-01
期刊：
影响因子：
7.2
通讯作者：
Lepiniec, Loic
中科院分区：
文献类型：
--
作者：
Baudry, Antoine;Caboche, Michel;Lepiniec, Loic
本研究对TT8表达的调控进行了研究，发现TT8表达是特异性激活类黄酮结构基因表达的重要调控步骤。首先，TT8::uidA构建物在植物中产生的GUS活性揭示了TT8启动子的细胞特异性激活，这与已知的TT8 bHLH因子参与原花青素、花青素和粘液的生物合成一致。此外，该报告结构的活性在ttg1、TT2过表达者（OE）和PAP1-OE中受到强烈影响，表明TT2、PAP1、ttg1与植物中TT8启动子的激活之间存在相互作用。为了进一步研究其中的机制，我们利用35S::TT2-GR和35S::TTG1-GR转基因植物（表达糖皮质激素受体融合蛋白）以及单杂交实验来确定这些因素对TT8表达的直接影响。有趣的是，体内TT2和PAP1与TT8启动子的结合依赖于TT8或同源bHLH因子GL3和EGL3的同时表达。与这些结果一致，TT8::uidA报告基因的活性在TT8突变体的种子内皮中受到强烈影响。同样，在gl3 x egl3突变体和PAP1蛋白显性阴性形式表达的植物中检测到TT8 mRNA水平的强烈下降，这表明TT8的表达受植物中MYB和bHLH因子的不同组合控制。讨论了这种正反馈机制在拟南芥种皮中强而特异地诱导原花青素生物合成中的重要性。
The control of TT8 expression was investigated in this study, and it was demonstrated that it constitutes a major regulatory step in the specific activation of the expression of flavonoid structural genes. First, the GUS activity generated in planta from a TT8::uidA construct revealed cell-specific activation of the TT8 promoter consistent with the known involvement of the TT8 bHLH factor in proanthocyanidin, anthocyanin and mucilage biosynthesis. Moreover, the activity of this reporter construct was strongly affected in ttg1, TT2 overexpressers (OE), and PAP1-OE, suggesting interplay between TT2, PAP1, TTG1 and the activation of the TT8 promoter in planta. To further investigate the mechanisms involved, we used 35S::TT2-GR and 35S::TTG1-GR transgenic plants (expressing fusion proteins with the glucocorticoid receptor), as well as one-hybrid experiments, to determine the direct effect of these factors on TT8 expression. Interestingly, in vivo binding of TT2 and PAP1 to the TT8 promoter was dependent on the simultaneous expression of TT8 or the homologous bHLH factors GL3 and EGL3. Consistent with these results, the activity of the TT8::uidA reporter was strongly affected in the seed endothelium of a tt8 mutant. Similarly, a strong decrease in the level of TT8 mRNA was detected in the siliques of a gl3 x egl3 mutant and in plants that express a dominant negative form of the PAP1 protein, suggesting that TT8 expression is controlled by different combinations of MYB and bHLH factors in planta. The importance of this positive feedback mechanism in the strong and specific induction of proanthocyanidin biosynthesis in the seed coat of Arabidopsis thaliana is discussed.