The acquisition of cell fate in the Arabidopsis thaliana root meristem

Abstract

During plant embryogenesis an embryo with cotyledons, a shoot apical meristem, a hypocotyl and a root apical meristem, is formed. The primary root and shoot meristems initiate post-embryonic growth generating all plant organs. The root meristem forms the primary root, and the shoot meristem forms the aerial portion of the plant including secondary meristems. Histological and fate map data have shown that there is no precise correlation between the shoot meristem cells and their descendants. This indicates that cell fate is flexible. In contrast, in the root a more strict relationship between differentiated cells and their meristematic ancestors is seen. Little is known about the mechanisms specifying cell fate in meristems. Here, we focus on the cellular communication that is critical for the formation and functioning of the Avabidopsis root meristem. Due to its simple cellular pattern, the Arabidopsis root is a suitable system to study cell specification and communication. We have used laser ablations to study the flexibility of cells in the root meristem. Furthermore, we have analysed a number of mutations involved in embryonic as well as secondary and adventitious root formation. Taken together, these results show that root meristem initials learn their fate by positional information and that genes involved in cell specification first act early during embryogenesis.