Summary In Arabidopsis thaliana, the asymmetric cell division (ACD) of the zygote gives rise to the embryo proper and an extraembryonic suspensor, respectively. This process is controlled by the ERECTA‐YODA‐MPK3/6 receptor kinase‐MAP kinase‐signaling pathway, which also orchestrates ACDs in the epidermis. In this context, the bHLH transcription factor ICE1/SCRM is negatively controlled by MPK3/6‐directed phosphorylation. However, it is unknown whether this regulatory module is similarly involved in the zygotic ACD. We investigated the function of SCRM in zygote polarization by analyzing the effect of loss‐of‐function alleles and variants that cannot be phosphorylated by MPK3/6, protein accumulation, and target gene expression. Our results show that SCRM has a critical function in zygote polarization and acts in parallel with the known MPK3/6 target WRKY2 in activating WOX8. Our work further demonstrates that SCRM activity in the early embryo is positively controlled by MPK3/6‐mediated phosphorylation. Therefore, the effect of MAP kinase‐directed phosphorylation of the same target protein fundamentally differs between the embryo and the epidermis, shedding light on cell type‐specific, differential gene regulation by common signaling pathways.

中文翻译：

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bHLH 转录因子 ICE1/SCRM 的磷酸化依赖性激活促进拟南芥合子的极化


摘要 在拟南芥中，受精卵的不对称细胞分裂 （ACD） 分别产生胚胎本身和胚外悬吊器。这个过程由 ERECTA-YODA-MPK3/6 受体激酶-MAP 激酶信号通路控制，该通路还协调表皮中的 ACD。在这种情况下，bHLH 转录因子 ICE1/SCRM 受 MPK3/6 定向磷酸化的负控制。然而，尚不清楚该调节模块是否同样参与合子 ACD。我们通过分析功能丧失的等位基因和不能被 MPK3/6 磷酸化的变体、蛋白质积累和靶基因表达的影响，研究了 SCRM 在受精卵极化中的功能。我们的结果表明，SCRM 在受精卵极化中具有关键功能，并且在激活 WOX8 中与已知的 MPK3/6 靶标 WRKY2 平行作用。我们的工作进一步证明，早期胚胎中的 SCRM 活性受 MPK3/6 介导的磷酸化的正向控制。因此，相同靶蛋白的 MAP 激酶定向磷酸化的影响在胚胎和表皮之间根本不同，揭示了共同信号通路的细胞类型特异性差异基因调控。