Positional information and mobile transcriptional regulators determine cell pattern in the Arabidopsis root epidermis

The root epidermis is a model system for deciphering the mechanism underpinning the formation of cellular pattern in planar groups of cells. The epidermis comprises rows of hair cells (H) and non-hair-bearing epidermal cells (N). Laser ablation and clonal analysis have shown that the fates of epidermal cells are flexible through development and that positional information which may be located in the cell wall or extracellular matrix determines cell fate. A leucine-rich repeat protein called SCRAMBLED is required for the development of cell pattern which may be involved in the perception of positional information. It is proposed that positional signals then initiate the cell-specific expression of a number of transcription factors that complete the patterning process, resulting in the expression of hair-promoting genes in hair cells (H) and their repression in the hairless cells (N).