The Phenylpropanoid Pathway Is Controlled at Different Branches by a Set of R2R3-MYB C2 Repressors in Grapevine
The Phenylpropanoid Pathway Is Controlled at Different Branches by a Set of R2R3-MYB C2 Repressors in Grapevine
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DOI：
10.1104/pp.114.256172
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发表时间：
2015-04-01
期刊：
影响因子：
7.4
通讯作者：
Tornielli, Giovanni Battista
中科院分区：
文献类型：
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作者：
Cavallini, Erika;Tomas Matus, Jose;Tornielli, Giovanni Battista
由于苯丙素类化合物具有广泛的功能，其合成需要在整个植物发育和对环境的响应中进行精确的时空协调。这些次级代谢物的积累受到 MYB 和碱性螺旋-环-螺旋蛋白家族的正负调节因子的转录控制。我们对来自 C2 阻遏蛋白基序进化枝的四种葡萄 (Vitis vinifera) R2R3-MYB 蛋白进行了表征，所有这些蛋白都含有乙烯反应因子相关的两亲性抑制结构域，但不同之处在于存在强黄酮类阻遏蛋白拟南芥 (Arabidopsis thaliana) AtMYBL2 中发现的额外 TLLLFR 抑制基序。 VvMYB4a和VvMYB4b在矮牵牛中的组成型表达抑制了一般苯丙素生物合成基因并选择性地减少了小重量酚类化合物的量。相反，表达VvMYBC2-L1和VvMYBC2-L3的转基因矮牵牛品系表现出花瓣花青素和种子原花青素的严重减少以及粗花瓣提取物的pH值较高。这些调节因子的独特功能通过在烟草（Nicotiana Benthamiana）叶和葡萄植株中的瞬时表达得到进一步证实。最后，转录组分析显示，VvMYBC2-L3 在葡萄毛状根中异位表达，显示原花青素含量降低以及类黄酮途径的结构和调节基因下调。通过结合功能分析结果及其在发育过程中和对紫外线 B 辐射的响应中葡萄树中的表达模式，推断出这些阻遏物的生理作用。我们的结果表明，VvMYB4a 和 VvMYB4b 可能在负调节小重量酚类化合物的合成中发挥关键作用，而 VvMYBC2-L1 和 VvMYBC2-L3 可能另外微调类黄酮水平，平衡转录激活剂的诱导作用。
Because of the vast range of functions that phenylpropanoids possess, their synthesis requires precise spatiotemporal coordination throughout plant development and in response to the environment. The accumulation of these secondary metabolites is transcriptionally controlled by positive and negative regulators from the MYB and basic helix-loop-helix protein families. We characterized four grapevine (Vitis vinifera) R2R3-MYB proteins from the C2 repressor motif clade, all of which harbor the ethylene response factor-associated amphiphilic repression domain but differ in the presence of an additional TLLLFR repression motif found in the strong flavonoid repressor Arabidopsis (Arabidopsis thaliana) AtMYBL2. Constitutive expression of VvMYB4a and VvMYB4b in petunia (Petunia hybrida) repressed general phenylpropanoid biosynthetic genes and selectively reduced the amount of small-weight phenolic compounds. Conversely, transgenic petunia lines expressing VvMYBC2-L1 and VvMYBC2-L3 showed a severe reduction in petal anthocyanins and seed proanthocyanidins together with a higher pH of crude petal extracts. The distinct function of these regulators was further confirmed by transient expression in tobacco (Nicotiana benthamiana) leaves and grapevine plantlets. Finally, VvMYBC2-L3 was ectopically expressed in grapevine hairy roots, showing a reduction in proanthocyanidin content together with the down-regulation of structural and regulatory genes of the flavonoid pathway as revealed by a transcriptomic analysis. The physiological role of these repressors was inferred by combining the results of the functional analyses and their expression patterns in grapevine during development and in response to ultraviolet B radiation. Our results indicate that VvMYB4a and VvMYB4b may play a key role in negatively regulating the synthesis of small-weight phenolic compounds, whereas VvMYBC2-L1 and VvMYBC2-L3 may additionally fine tune flavonoid levels, balancing the inductive effects of transcriptional activators.