Profiling chromatin accessibility during stomatal development

Plant cells are totipotent and hence can dedifferentiate and re-differentiate, making it possible to clone entire plant parts from a single cell. It is hence critical for plant cells to maintain specific cell-states during and after differentiation. Stomata, microscopic valves on the plant epidermis required for efficient gas exchange and water management, have emerged as a powerful model system for understanding how de novo lineage-specific stem cell initiate, proliferate and differentiate into specialized cell types during their development of the plant epidermis. The stomatal lineage emerged from a subpopulation of protodermal cells as meristemoid mother cells (MMCs) that undergoes an asymmetric entry division to give a rise meristemoid and its sister cell called the stomatal-lineage ground cell (SLGC). After several rounds of asymmetric cell division, meristemoids differentiate into round guard mother cells (GMC), which divide symmetrically and terminally differentiate into paired guard cells (GCs). We have adapted the INTACT (Isolation of Nuclei TAgged in Specific Cell Types) system to isolate each stomatal lineage-specific nuclei followed by ATACseq (Assay for Transposase-Accessible Chromatin). We showed that chromatin accessibility is dynamic throughout the stomatal lineage progression. Further, the analysis of TF binding sites in differentially accessible regions led to discover that combinatorial cis-regulatory elements and transcription factor circuits controls lineage specific cell state transition during stomatal development. Biotinylated nuclei were isolated from transgenic Arabidopsis thaliana Col-0 seedlings. Seedlings were harvested from 3day old seedlings containing the INTACT system under the cell type-specific promoter. To generate the ATACseq library, isolated nuclei were transposed with Tn5 from the Illumina Nextera Kit, followed by DNA purification. Purified transposed DNA was used for ATACseq library construction.