Embryo-patterning genes and reinforcement cues determine cell fate in the Arabidopsis thaliana root

The majority of plant organs arise from groups of continuously dividing cells, the meristems. Little is known about mechanisms of cell specification in meristems. Within the Arabidopsis root meristem, the fate of every cell can be predicted accurately, and the origin of these cells during the formation of the embryonic root primordium is known. Laser ablations reveal that, despite the regularity in cell lineage, position remains important to reinforce cell specification. Genetic analysis has revealed that many genes involved in the specification of the main cell types in the root act early, during embryogenesis, and an important question is whether the same or other genes are involved in the reinforcement of specification. Sub-specification of cell types, as exemplified by epidermal root hair cell specification, involves two pathways, one of which may act to reinforce earlier patterning events mediated by the other