Transcriptional Regulation of Zygote Asymmetry in Arabidopsis thaliana

植物发育的一个基本步骤是由一个单细胞受精卵产生胚和胚柄两个前体细胞。在许多物种中，包括模式植物拟南芥，合子极化并经历不对称分裂，产生这两个不同形态和命运的细胞，并使未来植物的顶-基（芽-根）轴明显。与动物不同，植物受精卵具有转录活性，包括调节其极性和不对称分裂的基因。这意味着植物必须进化出机制来激活受精后控制早期胚胎模式的受精卵特异性转录程序。在上一个资助期间，我们证明了这个激活过程需要每个亲本提供的转录信息的协作。从父系方面来看，精子传递的短悬索（SSP）膜蛋白mRNA触发转录因子WRKY2的磷酸化，这是合子核和液泡极性定位以及随后的不对称分裂所必需的。这些功能是通过受精后主模式基因WUSCHEL HOMEOBOX8 （WOX8）的直接转录上调介导的。我们进一步发现转录因子HOMEODOMAIN GLABROUS11/12 （HDG11/12）作为合子不对称的新型母体调节因子，也直接调节WOX8的转录。这些结果揭示了母体和父系因素如何整合在受精卵中以调节胚胎模式的框架。本提案的目标是深入了解这些过程是如何调节的。首先，我们将分析WRKY2和HDG11/12之间的蛋白-蛋白相互作用如何促进合子不对称的调节。其次，我们将讨论WOX8的转录激活如何局限于受精卵及其基础后代，而在胚胎后组织中受到抑制。第三，我们将探索合子中的转录程序如何转化为发育表型。为了研究这些问题，我们将结合遗传学、生物化学和分子生物学的方法。除了我们最近发表的发现，我们已经为这个提议做了大量的准备工作，包括转录组分析，相互作用研究和分子工具的准备，使我们的实验能够迅速开始。我们期望这项工作将为理解受精卵转录程序的启动及其对早期胚胎发育的影响提供重大进展。在更广泛的背景下，我们正在与国际实验室合作，将所获得的知识应用于通过体细胞胚胎形成改善经济上重要植物的再生策略。

One of the fundamental steps in plant development is the generation of the two precursor cells for embryo and suspensor from a single-celled zygote. In many species, including the model plant Arabidopsis, the zygote is polarized and undergoes an asymmetric division that generates these two cells of different morphologies and fates and makes the apical-basal (shoot-root) axis of the future plant evident. Unlike in animals, plant zygotes are transcriptionally active including genes regulating its polarity and asymmetric division. This implies that plants must have evolved mechanisms to activate zygote-specific transcription programs after fertilization that govern early embryo patterning. During the last funding period, we demonstrated that this activation process requires the collaboration of transcriptional information provided by each parent. From the paternal side, sperm-delivered mRNA of the SHORT SUSPENSOR (SSP) membrane protein triggers the phosphorylation of the transcription factor WRKY2, which is required for polar localization of nucleus and vacuoles in the zygote and subsequently for its asymmetric division. These functions are mediated by direct transcriptional up-regulation of the master patterning gene WUSCHEL HOMEOBOX8 (WOX8) after fertilization. We further discovered the transcription factors HOMEODOMAIN GLABROUS11/12 (HDG11/12) as novel maternal regulators of zygote asymmetry that also directly regulate WOX8 transcription. These results reveal a framework of how maternal and paternal factors are integrated in the zygote to regulate embryo patterning. The goal of this proposal is to gain insight into how these processes are regulated. First, we will analyze how protein-protein interaction between WRKY2 and HDG11/12 contribute regulation of zygote asymmetry. Second, we will address how transcriptional activation of WOX8 is confined to the zygote and its basal descendants but inhibited in postembryonic tissue. Third, we will explore how transcriptional programs in the zygote translate into developmental phenotypes. To investigate these questions, we will combine genetic, biochemistry and molecular biology approaches. In addition to our recently published finding, we have already done extensive preparatory work for this proposal, including transcriptome analysis, interaction studies and preparation of molecular tools, enabling a swift start of the proposed experiments.We expect that this work will provide significant advances in understanding the initiation of transcriptional programs in the zygote and their impact on early embryo development. In a broader context, we are collaborating with international laboratories to apply the obtained knowledge for improving regeneration strategies of economically important plants through somatic embryo formation.