What is it about?
In many plants, the asymmetric division of the zygote sets up the apical-basal body axis. In the cress Arabidopsis, the zygote co-expresses regulators of the apical and basal embryo lineages, the transcription factors WOX2 and WRKY2/WOX8, respectively. WRKY2/WOX8 activity is controlled by biparental input and promotes nuclear migration, cellular polarity, and mitotic asymmetry of the zygote, which are hallmarks of axis formation in many plant species. However, the role of WOX2 and how the antagonistic WOX2 and WRKY2/WOX8 functions are integrated in the zygote have remained a long-standing question. Here, we report that WOX2 loss-of-function completely suppresses the reduced zygote asymmetry of wrky2 mutants and that WOX2 overexpression mimics the wrky2 phenotype. At the molecular level, WRKY2 downregulates WOX2 transcription in the zygote and the basal embryo lineage, in addition to promoting WOX8 expression. WOX2 antagonizes WRKY2 function by repressing WOX8 transcription. As a physiological readout, the WRKY2/WOX8-WOX2 balance regulates the integrity of F-actin cables in the zygote, providing a mechanistic framework for the role of WRKY2/WOX8-WOX2-mediated zygote asymmetry.
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Why is it important?
Our results provide insight into the long-standing question of how the functions of apical and basal embryo lineage regulators are integrated in the Arabidopsis zygote: WRKY2 represses WOX2 transcription, which keeps the inhibition of WRKY2-activated WOX8 transcription by WOX2 at bay. WOX8 activity then promotes actin-mediated migration of the nucleus to the apical half of the zygote, setting the position of the cell division plane that separates apical and basal embryo lineages. The wiring logic of this module constitutes a coherent feed-forward loop, which has the potential to stabilize WOX8 output in the zygote against input noise.
Perspectives
This zygotic WRKY2/WOX8/9-WOX2 balance is disrupted after the zygotic division when the basal daughter is dominated by WRKY2/WOX8/9 output and the apical by WOX2. How the two antagonistic activities segregate into the two daughter cells remains to be investigated.
Feng Xiong
Shandong Agricultural University
Read the Original
This page is a summary of: Integration of basal and apical embryo lineage regulators controls F-actin cable integrity and zygote asymmetry in
Arabidopsis, Proceedings of the National Academy of Sciences, December 2024, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2402720122.
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