Initiation of shoot meristem stem cells during Arabidopsis embryogenesis

• Applicant: Professor Dr. Thomas Laux
• Subject Area: Plant Cell and Developmental Biology
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 421046375

How does an organism establish pluripotent stem cells? This central step in plant and animal development underlies the lifelong production of cells and tissues. However, while the regulation of postembryonic stem cell maintenance has been investigated in detail, relatively little is known about the initiation of stem cells during embryogenesis. In higher plants, the stem cells of the shoot meristem provide the cells for the formation of leaves, side branches, or flower buds throughout the plant's life. In our preparatory work, we showed that the initiation of the shoot meristem stem cell program is controlled by the WOX2 transcription factor, in part through balancing the phytohormones cytokinin and auxin. We found that WOX2 is expressed only in the outermost cell layer of the embryo at the stage of stem cell establishment, suggesting that this layer serves as a signaling source to switch the underlying cells to the stem cell program. Finally we isolated protein interactors of WOX2 that may explain how WOX2 functions in stem cell initiation. These results provide an exciting opportunity to reveal the fundamental molecular mechanisms underlying shoot meristem stem cell initiation in plants. The goal of this proposal is to gain insight into how WOX2 regulates stem cell initiation in Arabidopsis embryogenesis. First, we will identify and characterize direct WOX2 target genes during stem cell initiation using genome-wide chromatin and transcriptome analysis. Second, we will investigate the molecular mechanisms by which WOX2 regulates transcription and test the hypothesis that it is an epigenetic regulator. Third, we will explore whether the three layers of shoot meristem stem cells are programmed by WOX2 through a signaling mechanism from the outer cell layer or through an epigenetic memory mechanism. Fourth, we will investigate already isolated protein interactors of WOX2 to analyze which mechanisms enable WOX2 to initiate stem cells. 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 protein 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 shoot meristem stem cell in Arabidopsis. Because paralogs of WOX2 are conserved elements in regulated also root and cambium stem cells and because stem cell regulation by WOX proteins is conserved at least in higher plants, we expect that our findings will contribute to our understanding of stem cell initiation in general in plants. Furthermore, in addition to elucidating a fundamental process in plant stem cell development, we collaborate with our international colleagues to incorporate our results into plant regeneration strategies which are important tools in plant breeding.

• DFG Programme: Research Grants