Root stem cells: how to establish and maintain the eternal youth

Differently from animals, most of the plant organs are generated during post-embryonic development. This depends on meristems, regions located at the distal sides of the plants. In the meristems a set of self-renewal stem cells divides asymmetrically providing new cells to the growing organs. During embryogenesis, the acquisition of stem cell identity by two different sets of cells located at the basal and apical pole of the embryo, guarantees the generation of the primary meristems: the shoot apical meristem (SAM) and the root apical meristem (RAM). During post-embryonic growth these sets of stem cells are maintained and give rise to all organs of the mature plant, sustaining its growth. Here we review the state of the art on the actual knowledge on root stem cells. In particular, we focus on those mechanisms that permit stem cell fate acquisition and that allow their fate maintenance during growth, and how interspecific variability of stem cells activity provides differences in species-specific anatomical features.