Root Cell Differentiation in Arabidopsis
P-21
Roots grow in a simple manner via an organized pattern of cell division and differentiation. In our laboratory, we use the Arabidopsis root epidermis as a particularly useful model tissue for studying the regulation of cell differentiation. This tissue contains a single cell layer with only two morphologically distinct cell-types (root-hair cells and non-hair cells), and it forms rapidly and continuously after seed germination. Furthermore, mutations affecting the formation of either epidermal cell type do not affect plant viability. The hair and non-hair cell types arise in a position-dependent pattern that implies cell-cell interactions are critical for cell fate specification. We have identified and analyzed several genes that influence the position-dependent patterning of the epidermal cell types. Some of these genes (e.g. GLABRA2 and WEREWOLF) encode transcription factors important for non- hair cell specification, whereas others (e.g. CAPRICE and TRIPTYCHON) help define the hair cell type. By studying the expression and interactions between these genes, we have found that transcriptional feedback loops between them are important in establishing the cell type pattern. The WEREWOLF gene product is a positive regulator of both GLABRA2 and CAPRICE gene expression. During epidermis development, positional cues apparently bias the WER expression and cause a relatively high level of GLABRA2 and CAPRICE expression in cells located in a particular location (the N cell position), which leads to the non-hair cell fate. The truncated MYB encoded by CAPRICE mediates a lateral inhibition mechanism to negatively regulate WEREWOLE, GLABRA2, and CAPRICE gene expression in the alternate position (the H cell position), which leads to the hair fate. These findings provide a molecular genetic framework for understanding the determination of a cell type pattern in plants.
J. SCHlEFELBEIN, Christine Bernhardt, Christa Carozzo, Su-Hwan Kwak, Myeong Min Lee, Ronglai Shen, and Marissa Simon. Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109. E-mail: schiefel@umich.edu
Copyright Society for In Vitro Biology Spring 2004