Transcriptional Regulation of Zygote Asymmetry in Arabidopsis thaliana

• Applicant: Professor Dr. Thomas Laux
• Subject Area: Plant Cell and Developmental Biology
• Term: from 2017 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 392561620

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.

• DFG Programme: Research Grants