Regulation of the asymmetric division of the Arabidopsis thaliana zygote by the WRKY2 pathway

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The polarity of the Arabidopsis embryo along the apical-basal axis can be traced back to the polarity and the asymmetric division of the zygote. This division gives rise to two daughter cells of different fates: the small apical daughter will form most of the embryo, whereas the large basal daughter generates the extra embryonic suspensor and its progeny contributes to the embryonic root. However, the mechanisms of how different cell fates arise from the polarized zygote are unknown. In this project we will address the molecular organization of the zygote and how as a consequence different daughter cell fates are generated. We have identified two homeobox genes, ZOX1 and ZOX3, whose mRNA localization reflects the asymmetric division of the zygote and are likely to establish different gene expression programs in their daughters. ZOX1 and ZOX3 thus can be used as tools to study zygote polarity and the mechanisms of how this polarity is translated into different embryonic cell fates. Both mRNAs are present in the egg cell and the zygote. After cell division, ZOX1 mRNA is located only in the apical and ZOX3 mRNA only in the basal daughter of the zygote. Our preliminary results indicate that this asymmetric localization of ZOX mRNAs is established at the level of the zygote already. Our working hypothesis, to be tested in this project, is that the zygote contains both apical and basal cell fate determinants, the asymmetric localization of which contributes to the generation of the different fates of its daughters.