Root Epidermal Development in Arabidopsis

© 2010 Blackwell Publishing Ltd. All rights reserved. The root epidermis is the layer of cells that surrounds the mature root before it undergoes secondary thickening and is an active interface between the plant and the soil environment. The epidermis develops early in embryogenesis along with the rest of the root meristem (radicle). Upon germination, it emerges from below the protective root cap and differentiates into hair and hairless epidermal cells. Hair cells serve to increase the surface area of the root across which water and nutrients can be transported and are the sites where the plant first makes contacts with a range of microorganisms, including the nitrogen-fixing bacteria of the genus Rhizobium. There is an enormous diversity of root epidermis types among the land plants but for the purposes of this chapter, we will focus largely on the development of the epidermis of Arabidopsis. First, we will describe the earliest stages of epidermal development in the embryo. Then, we will define the functions of a number of genes that are required for the maintenance of epidermal identity in the postembryonic seedling root and the mechanism that gives rise to the patterned array of hair and hairless cells in the epidermis. Finally, we will consider the mechanism of root hair morphogenesis and the effect of environmental factors, such as inorganic phosphate and iron, on root hair development in both Arabidopsis and some crop species.