Role of the CLE40-ACR4 signalling module in Arabidopsis root development

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The growth of plant roots is controlled by meristems that constantly generate new cells. These cells later specialize for their individual tasks, such as nutrient uptake, water transport, or protection of the growing root tip. The Arabidopsis root consists of cells arranged in regular cell files, which originate from stem cells at the root tip. Divisional activity of stem cells and differentiation of their daughter cells has to be coordinated, which is achieved through the exchange of signals such as the phytohormone auxin and small peptides. The peptide CLE40 is secreted by differentiated columella cells. It is perceived by the receptor protein ACR4 that resides on the plasma membrane of columella stem cells and controls expression of the transcription factor WOX5. WOX5 is in turn required to inhibit the columella stem cells from premature differentiation. Together, CLE40, ACR4 and WOX5 establish a regulatory module that controls cell behavior in the root meristem. We intend to analyse how the components of this module interact, their intersection with auxin signaling pathways, and the target genes that are regulated by this module and ultimately control a cells decision to further divide or differentiate. To understand the functioning of the CLE40-ACR4-WOX5 module, we will change the activity of the individual components, study their mutual transcription regulation, and investigate transcriptional control regions in their promoters. Input from hormone signalling pathways will be investigated by hormone treatments or inhibiton of hormone function and transport. Target genes and their activity will be identified by next-generation sequencing approaches, and by the generation of appropriate mutant lines.