Minimum Requirements for Changing and Maintaining Cell Fate in the Arabidopsis Root

Abstract

A cell’s trajectory from stem cell to differentiation, while often portrayed as a linear progression, is best described as a network that produces a mature state through several pathways acting together. There are few examples that describe gene regulatory network changes during the entire trajectory of cell differentiation. The goal of my project was to define the gene regulatory network required for a stem cell to become a differentiated cell in the Arabidopsis thaliana root. The root is a powerful model for identifying basic principles of differentiation. Plant cells do not migrate therefore entire lineages from stem cell to mature progeny are spatially confined. Furthermore, the root displays indeterminate growth, facilitating the study of many different developmental stages at a single time. One cell type of the root, the endodermis, is particularly suitable for study because the molecular components required for its formation and terminal differentiation are established. In order to understand the path from stem cell to differentiated cell in the endodermis, we asked what transcription factors are sufficient to program a non-native cell-type into endodermis. Our results show the transcription factors SHORTROOT and MYB36 have limited ability to reprogram a non-native cell-type (the epidermis) and that this reprogramming is reversible in the absence of additional cues. The stele-derived signaling peptide CIF2 stabilizes SHORTROOT-induced reprogramming. The outcome is a partially impermeable barrier deposited in the sub-epidermal cell layer that has a transcriptional signature similar to endodermis. The induction mechanism depends on MYB36 and CIF2’s receptor, but may be independent of the transcription factor SCARECROW. These results highlight a non cell-autonomous induction mechanism for endodermis that resembles differentiation in many animal systems.