Abstract

The study of the concerted action of hormones and transcription factors is fundamental to understand cell differentiation and pattern formation during organ development. The root apical meristem of Arabidopsis thaliana is a useful model to address this. It has a stem cell niche near its tip conformed of a quiescent organizer and stem or initial cells around it, then a proliferation domain followed by a transition domain, where cells diminish division rate before transiting to the elongation zone; here, cells grow anisotropically prior to their final differentiation towards the plant base. A minimal model of the gene regulatory network that underlies cell-fate specification and patterning at the root stem cell niche was proposed before. In this study, we update and couple such network with both the auxin and cytokinin hormone signaling pathways to address how they collectively give rise to attractors that correspond to the genetic and hormonal activity profiles that are characteristic of different cell types along A. thaliana root apical meristem. We used a Boolean model of the genetic-hormonal regulatory network to integrate known and predicted regulatory interactions into alternative models. Our analyses show that, after adding some putative missing interactions, the model includes the necessary and sufficient components and regulatory interactions to recover attractors characteristic of the root cell types, including the auxin and cytokinin activity profiles that correlate with different cellular behaviors along the root apical meristem. Furthermore, the model predicts the existence of activity configurations that could correspond to the transition domain. The model also provides a possible explanation for apparently paradoxical cellular behaviors in the root meristem. For example, how auxin may induce and at the same time inhibit WOX5 expression. According to the model proposed here the hormonal regulation of WOX5 might depend on the cell type. Our results illustrate how non-linear multi-stable qualitative network models can aid at understanding how transcriptional regulators and hormonal signaling pathways are dynamically coupled and may underlie both the acquisition of cell fate and the emergence of hormonal activity profiles that arise during complex organ development.

Highlights

  • The root apical meristem (RAM) of A. thaliana is an important model for understanding the complex mechanisms underlying cell differentiation and morphogenesis during organ development of multicellular organisms [1,2,3,4,5,6,7,8]

  • We proposed a minimal network model that integrates the regulatory cross-talk among the auxin and cytokinin signaling pathways with the main studied transcriptional regulators operating during the establishment and organization of the A. thaliana root apical meristem

  • Our model suggests that when a cell acquires a particular cell fate it may acquire a differential capacity to respond to a particular hormone

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Summary

Introduction

The root apical meristem (RAM) of A. thaliana is an important model for understanding the complex mechanisms underlying cell differentiation and morphogenesis during organ development of multicellular organisms [1,2,3,4,5,6,7,8]. The progeny of the rest of the initial cells divide at higher rates in the PD towards the base of the plant. These cells transit to the TD where they divide at slower rates and begin to endoreduplicate [17,18,19]

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