SHORT-RANGE CONTROL OF CELL-DIFFERENTIATION IN THE ARABIDOPSIS ROOT-MERISTEM

Meristems are distinctive regions of plants that have capacity for con tinuous growth. Their developmental activity generates the majority of plant organs(1). It is currently unknown how cell division and cell d ifferentiation are orchestrated in meristems, although genetic studies have demonstrated the relevance of a proper balance between the two p rocesses(2-6), Root meristems contain a distinct central region of mit otically inactive cells, the quiescent centre(7), the function of whic h has remained elusive until now. Here we present laser ablation and g enetic data that show that in Arabidopsis thalinna the quiescent centr e inhibits differentiation of surrounding cells. Differentiation regul ation occurs within the range of a single cell, in a manner strikingly similar to examples in animal development, such as during delaminatio n of Drosophila neuroblasts(8). Our data indicate that pattern formati on in the root meristem is controlled by a balance between short-range signals inhibiting differentiation and signals that reinforce cell fa te decisions(9).