Initiating inhibition. Control of epidermal cell patterning in plants.

Abstract

A recent publication by Schellmann et al . (2002) in The EMBO Journal has provided important insights into the control of cell fate and pattern formation in plants. To study the underlying molecular mechanisms, the authors made use of the development of root hairs and trichomes in Arabidopsis thaliana . A. thaliana trichomes are large, unicellular structures that project out from the shoot epidermal surface and are thought to form a defence against herbivorous insects. Root hairs are specialized cells extending from the root epidermis and are important for water and mineral uptake. The positional cues that regulate the spacing of trichomes and root hairs are unique. In the root, positional information is derived from the location of the epidermal cells relative to underlying cortex cells (Fig. 1A). Epidermal cells that are located over a junction between two cortex cells become root hairs (H cells), whereas the other epidermal cells become non‐root‐hair cells (N cells). On the leaves, the trichome spacing pattern is determined largely by the position of the first trichome (Fig. 1B). After the leaf primordium reaches a length of ∼100 μm, a single epidermal cell at the leaf tip becomes a trichome. Thereafter, a regulated spacing pattern evolves in which newly initiated trichomes are approximately equal distance from one another. As older trichomes become separated by epidermal cell divisions, new intervening trichomes emerge (Fig. 1B). Figure 1. Epidermal patterning of roots and leaves. ( A ) Line drawing of a cross‐section of a mature region of an Arabidopsis root. Epidermal and cortical cell layers are labelled. H, root‐hair cell; N, non‐root‐hair cell. …