The role of cell identity in the response to cell wall perturbation in the Arabidopsis thaliana primary root

The cell wall is a defining feature of plant cells. It is a rigid, yet flexible, layer surrounding each cell outside the plasma membrane and is mainly composed of polysaccharides such as cellulose, hemicellulose, and pectin, as well asm to a lesser extent, phenolic compounds such as lignin and structural proteins. Plant cell wall is central to nearly all aspects of plant. Its biosynthesis and remodeling are essential for cell division, expansion and differentiation, the fundamental events through plant growth and development. In brief, cell walls shape the cells, which is crucial for organ formation, provide mechanical support to the plant, control cell-to-cell adhesion, form the interface between cells, which is indispensable for cellular communication, and regulate plant-pathogen/environment interactions. As plants permanently face intrinsic and extrinsic cues from developmental programs and the environment, this information must be correctly conveyed into the cells in order to adjust the plant’s growth behavior and reallocate the resources accordingly. Therefore, a cell wall surveillance and signalling system must exist to ensure transmission of the information. Roots form the hidden half of the plant and perform numerous physical and physiological functions such as anchoring, nutrient uptake and transport. The primary root of the model organism in plant research, Arabidopsis thaliana, is formed with different tissues organized as longitudinal cell files that are radially patterned in a concentric manner, which provides an easily accessible model to study plant development. By using this model, previous studies in our lab have revealed the plasma membrane residing RECEPTOR LIKE PROTEIN (RLP)44 as key factor for cell wall surveillance and signalling. RLP44 monitors pectin status in the cell wall and transduces the signal of changes in cell wall integrity through interaction with the brassinosteroid receptor BRI1, which in turn activates a well-described signalling cascade to regulate plant growth transcriptionally. As in plants, different tissues fulfill distinct biological functions and have similar, yet distinguishable, characteristics in their cell walls, investigation of RLP44-mediated cell wall signalling in tissue-specific context would bring more insights into how plants co-ordinates its growth and development in responses to cell wall changes at tissue level. To do so, we made use of the recently developed GreenGate cloning technique and the dexamethasone-inducible system pOp6/GR-LhG4. By using promoters driving expression specifically in different cell types/ tissues, we ectopically expressed pectin-modifying gene PECTIN METHYLESTERASE INHIBITOR 5 (PMEI5) and studied the responses of the plant to the loss of cell wall integrity. Here, we showed that cell wall homeostasis had pronounced impact on root growth, especially on in root morphogenesis, meristem size control, division plane determination through CDS maintenance, and tissue patterning. This influence was manifested as varying phenotypes at tissue level, implemented probably through crosstalks between brassinosteroid and other hormone signalling pathways in both cell-autonomous and non cell-autonomous manner. Besides, the previously described RLP44-mediated cell wall signalling exerts its role in a cell type/tissue-specific way and other cell wall sensing and signalling mechanisms are also possibly involved in the responses to cell wall perturbation. However, biochemical and histological characterization of cell wall properties as well as genetic studies for discovering the underlying molecular mechanisms will be necessary to further understand the role of cell identity in cell wall signalling and plant growth regulation