The phosphorylation status of MYB75 at T-131 affects protein stability, flavonoid profiles, and patterns of gene expression. The Arabidopsis transcription factor Myeloblastosis protein 75 (MYB75, AT1G56650) is known to act as a positive transcriptional regulator of genes required for flavonoid and anthocyanin biosynthesis. MYB75 was also shown to negatively regulate lignin and other secondary cell wall biosynthetic genes (Bhargava et al. in Plant Physiol 154(3):1428–1438, 2010). While transcriptional regulation of MYB75 has been described in numerous publications, little is known about post-translational control of MYB75 protein function. In a recent publication, light-induced activation of a MAP kinase (MPK4, AT4G01370) in Arabidopsis was reported to lead to MYB75 phosphorylation at two canonical MPK target sites, threonines, T-126 and T-131. This double phosphorylation event positively influenced MYB75 protein stability (Li et al. in Plant Cell 28(11):2866–2883, 2016). We have examined this phenomenon through use of phosphomutant forms of MYB75 and found that MYB75 is phosphorylated primarily at T-131, and that the phosphorylation of MYB75 recombinant protein in vitro can be catalyzed by multiple MAP kinases, including MPK3 (AT3G45640), MPK6 (AT2G43790), MPK4 and MPK11 (AT1G01560). We also demonstrate that MYB75 can bind to a large number of Arabidopsis MPK’s in vitro, suggesting it could be a target of multiple signalling pathways. The impact of MYB75 phosphorylation at T-131 on the function of this transcription factor, in terms of localization, stability, and protein–protein interactions with known binding partners was examined in transgenic lines expressing phosphomimic and phosphonull versions of MYB75, to capture the behaviour of permanently phosphorylated and unphosphorylated MYB75 protein, respectively. In addition, we describe how ectopic over-expression of different phosphovariant forms of MYB75 (MYB75WT, MYB75T131A, and MYB75T131E) affects flavonoid biochemical profiles and global changes of gene expression in the corresponding transgenic Arabidopsis plants.

中文翻译：

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磷模拟 AtMYB75 的生物学影响

MYB75 在 T-131 的磷酸化状态会影响蛋白质稳定性、类黄酮谱和基因表达模式。已知拟南芥转录因子成髓细胞增多症蛋白 75 (MYB75, AT1G56650) 可作为类黄酮和花青素生物合成所需基因的正转录调节因子。MYB75 还显示出负调节木质素和其他次生细胞壁生物合成基因（Bhargava 等人在 Plant Physiol 154(3):1428–1438, 2010）。虽然 MYB75 的转录调控已在许多出版物中进行了描述，但对 MYB75 蛋白功能的翻译后控制知之甚少。在最近的一份出版物中，据报道，拟南芥中 MAP 激酶（MPK4，AT4G01370）的光诱导激活导致 MYB75 在两个典型的 MPK 靶位点，苏氨酸，T-126 和 T-131 处磷酸化。这种双重磷酸化事件对 MYB75 蛋白稳定性产生了积极影响（Li et al. in Plant Cell 28(11):2866–2883, 2016）。我们通过使用 MYB75 的磷酸突变体形式检查了这一现象，发现 MYB75 主要在 T-131 处被磷酸化，并且体外 MYB75 重组蛋白的磷酸化可由多种 MAP 激酶催化，包括 MPK3 (AT3G45640)、MPK6 ( AT2G43790)、MPK4 和 MPK11 (AT1G01560)。我们还证明 MYB75 可以在体外与大量拟南芥 MPK 结合，这表明它可能是多种信号通路的靶标。T-131 的 MYB75 磷酸化对该转录因子功能的影响，在定位、稳定性、在表达 MYB75 磷酸模拟和磷酸缺失版本的转基因系中检查了与已知结合配偶体的蛋白质-蛋白质相互作用，以分别捕获永久磷酸化和未磷酸化 MYB75 蛋白的行为。此外，我们描述了 MYB75（MYB75WT、MYB75T131A 和 MYB75T131E）的不同磷酸变体形式的异位过表达如何影响相应转基因拟南芥植物中类黄酮的生化谱和基因表达的全局变化。