ABSTRACT The Arabidopsis transcription factor Myeloblastosis protein 75 (MYB75, AT1G56650) is a well-established transcriptional activator of genes required for anthocyanin and flavonoid production, and a repressor of lignin and other secondary cell wall biosynthesis genes. MYB75 is itself tightly regulated at the transcriptional, translational and post-translational levels, including protein phosphorylation by Arabidopsis MAP kinases Examination of the behavior of different phosphovariant versions of MYB75 in vitro and in vivo revealed that overexpression of the MYB75T131E phosphovariant had a particularly marked effect on global changes in gene expression suggesting that phosphorylated MYB75 could be involved in a broader range of functions than previously recognized. Here, we describe a range of distinct developmental phenotypes observed among Arabidopsis lines expressing various phosphovariant forms of MYB75. Expression of either MYB75T131E or MYB75T131A phosphovariants, from the endogenous MYB75 promoter, in Arabidopsis myb75− mutants (Nossen background), resulted in severely impaired germination rates, and developmental arrest at early seedling stages. Arabidopsis plants overexpressing MYB75T131E from a strong constitutive Cauliflower mosaic virus (CaMV35S) promoter displayed slower development, with delayed bolting, flowering and onset of senescence. Conversely, MYB75T131A -overexpressing lines flowered and set seed earlier than either Col-0 WT controls or other MYB75-overexpressors (MYB75WT and MYB75T131E ). Histochemical analysis of mature stems also revealed ectopic vessel development in plants overexpressing MYB75; this phenotype was particularly prominent in the MYB75T131E phosphovariant. These data suggest that MYB75 plays a significant role in plant development, and that this aspect of MYB75 function is influenced by its phosphorylation status.

中文翻译：

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表达 AtMYB75 磷酸变体的拟南芥植物的发育表型

摘要拟南芥转录因子成髓细胞蛋白 75 (MYB75, AT1G56650) 是一种成熟的转录激活因子，可激活花青素和类黄酮生产所需的基因，也是木质素和其他次生细胞壁生物合成基因的阻遏物。MYB75 本身在转录、翻译和翻译后水平受到严格调控，包括拟南芥 MAP 激酶对蛋白质的磷酸化 体外和体内 MYB75 不同磷酸化变体版本的行为检查表明，MYB75T131E 磷酸化变体的过表达具有特别显着的影响基因表达的整体变化表明磷酸化的 MYB75 可能涉及比以前认识到的更广泛的功能。这里，我们描述了在表达各种磷酸化变异形式 MYB75 的拟南芥系中观察到的一系列不同的发育表型。来自内源性 MYB75 启动子的 MYB75T131E 或 MYB75T131A 磷酸变体在拟南芥 myb75− 突变体（Nossen 背景）中的表达导致发芽率严重受损，并在幼苗早期发育停滞。从强组成型花椰菜花叶病毒 (CaMV35S) 启动子过表达 MYB75T131E 的拟南芥植物表现出较慢的发育，具有延迟抽薹、开花和开始衰老。相反，过表达 MYB75T131A 的品系比 Col-0 WT 对照或其他 MYB75 过表达子（MYB75WT 和 MYB75T131E）开花和结籽更早。成熟茎的组织化学分析还揭示了过表达 MYB75 的植物中的异位血管发育；这种表型在 MYB75T131E 磷酸化变体中尤为突出。这些数据表明 MYB75 在植物发育中起着重要作用，并且 MYB75 功能的这一方面受其磷酸化状态的影响。