Two ways to skin a plant: The analysis of root and shoot epidermal development in Arabidopsis

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Abstract
The post‐embryonic architecture of higher plants is derived from the activity of two meristems that are formed in the embryo: the shoot meristem and the root meristem. The epidermis of the shoot is derived from the outermost layer of cells covering the shoot meristem through repeated anticlinal divisions. By contrast, the epidermis of the root is derived from an internal ring of cells, located at the centre of the root meristem, by a precise series of both periclinal and anticlinal divisions. Each epidermis has an independent origin. In Arabidopsis the mature shoot epidermis is composed of a small number of cell types: hair cells (trichomes), stomatal guard cells and other epidermal cells. In shoots, hairs take the form of branched trichomes that are surrounded at their base by a ring of accessory cells in a sheet of epidermal cells. The root epidermis is composed of two cell types: trichoblasts that form root hair cells and atrichoblasts that form non‐hair cells. Mutations affecting both the patterning and the morphogenesis of cells in both shoot and root epidermis have recently been described. Most of these mutations affect development in a single epidermis, but at least one, ttg, is involved in development in both epidermal systems.