Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, 20 Nanxin Cun, Xiangshan, Beijing, China.
Biochimie. 2011 Jul;93(7):1179-86. doi: 10.1016/j.biochi.2011.04.012. Epub 2011 Apr 30.
The subgroup 4 of R2R3-MYB transcription factors has been proposed as repressors regulating the phenylpropanoid pathway. Here, we report a cDNA encoding a subgroup 4 R2R3-MYB factor from wheat, designated as TaMYB4. A phylogenetic analysis showed that TaMYB4 is in a subclade that is specific to monocot plants. The TaMYB4 gene was highly expressed in stem and root tissues. In vitro binding analysis in yeast cells showed TaMYB4 interacted with OsCAD2 promoter characterized by an AC-II element that has been considered as the MYB-binding site in lignin biosynthetic genes. The overexpression of TaMYB4 in transgenic tobacco led to transcriptional reduction of both cinnamyl alcohol dehydrogenase (CAD) and cinnamoyl-CoA reductase (CCR) genes involved in the lignin biosynthesis. Enzymatic assay showed reduction of CAD and CCR activities in the transgenic tobacco plants that substantially decreased the levels of total lignin but increased it's ratio of S/G. In addition, the total flavonoid content was increased in transgenic tobacco leaves, suggesting that the overexpression of TaMYB4 likely led to a redirection of the metabolic flux from the lignin pathway to the flavonoid pathway. These data suggest that TaMYB4 negatively regulates the lignin biosynthesis in wheat.
R2R3-MYB 转录因子亚组 4 被提议为调节苯丙烷途径的抑制剂。在这里，我们从小麦中报告了一个编码亚组 4 R2R3-MYB 因子的 cDNA，命名为 TaMYB4。系统发育分析表明，TaMYB4 位于单子叶植物特有的亚分支中。TaMYB4 基因在茎和根组织中高度表达。在酵母细胞中的体外结合分析表明，TaMYB4 与 OsCAD2 启动子相互作用，该启动子具有被认为是木质素生物合成基因中 MYB 结合位点的 AC-II 元件。TaMYB4 在转基因烟草中的过表达导致参与木质素生物合成的肉桂醇脱氢酶 (CAD) 和肉桂酰辅酶 A 还原酶 (CCR) 基因的转录减少。酶活性测定表明，转基因烟草植物中的 CAD 和 CCR 活性降低，导致总木质素水平降低，但 S/G 比增加。此外，转基因烟草叶片中的总类黄酮含量增加，表明 TaMYB4 的过表达可能导致代谢通量从木质素途径转向类黄酮途径。这些数据表明 TaMYB4 负调控小麦中的木质素生物合成。
