The homeobox gene GLABRA 2 is required for position-dependent cell differentiation in the root epidermis of Arabidopsis thaliana

Abstract

The role of the Arabidopsis homeobox gene, GLABRA 2 (GL2), in the development of the root epidermis has been investigated. The wild-type epidermis is composed of two cell types, root-hair cells and hairless cells, which are located at distinct positions within the root, implying that positional cues control cell-type differentiation. During the development of the root epidermis, the differentiating root-hair cells (trichoblasts) and the differentiating hairless cells (atrichoblasts) can be distinguished by their cytoplasmic density, vacuole formation, and extent of elongation. We have determined that mutations in the GL2 gene specifically alter the differentiation of the hairless epidermal cells, causing them to produce root hairs, which indicates that GL2 affects epidermal cell identity. Detailed analyses of these differentiating cells showed that, despite forming root hairs, they are similar to atrichoblasts of the wild type in their cytoplasmic characteristics, timing of vacuolation, and extent of cell elongation. The results of in situ nucleic acid hybridization and GUS reporter gene fusion studies show that the GL2 gene is preferentially expressed in the differentiating hairless cells of the wild type, during a period in which epidermal cell identity is believed to be established. These results indicate that the GL2 homeodomain protein normally regulates a subset of the processes that occur during the differentiation of hairless epidermal cells of the Arabidopsis root. Specifically, GL2 appears to act in a cell-position-dependent manner to suppress hair formation in differentiating hairless cells.

Enhancing Our Understanding of Plant Cell-to-Cell Interactions Using Single-Cell Omics

“…This observation is supported by the role of these genes in controlling the differentiation of H cells notably by repressing the expression of GL2 (Kurata et al, 2005). Indeed, we did not detect any GL2 transcripts, nor TRY, into the cells and nuclei composing the trichoblast cluster as supported by previously published works (Rerie et al, 1994;Di Cristina et al, 1996;Masucci et al, 1996). This transcriptomic analysis at the single-cell level supports functional genomic studies showing the co-expression of major regulatory genes controlling the differentiation process and patterning of the root epidermal cells.…”

Basic Helix-Loop-Helix (bHLH) Transcription Factors Regulate a Wide Range of Functions in Arabidopsis

“…GL2, a member of homeodomain-leucine zipper (HD-ZIP) protein, affects the epidermal cell fate including in trichomes, root hair and the seed coat. It represses the transcription of RHD6 to inhibit hair formation in N-cells (non-root hair cells), leading to the expression of non-hair genes [42,45]. The bHLH transcription factor GL3 (GLABRA3, bHLH1) has similar functions, regulating its own transcription and downstream target genes to trigger the trichome initiation pathways, ENHANCER OF GLABRA3 (EGL3, bHLH2) plays partially redundant roles with GL3 in root hair [46,118].…”

Genetic and Molecular Analysis of Root Hair Development in Arabis alpina

“…In A. thaliana, the R2R3MYB transcription factor WER (Lee and Schiefelbein, 1999) and the WD40 protein TTG1 (Galway et al, 1994) form a complex with the bHLH proteins GL3/ EGL3 (Payne et al, 2000;Zhang et al, 2003) that activates the expression of GL2, which in turn suppresses root hair development in non-root hair cells (Masucci et al, 1996).…”

“…H-file cells (trichoblasts) and N-file cells (atrichoblasts) differ from early development. Trichoblasts display a higher cell division rate (Berger et al, 1998), reduced cell length (Dolan et al, 1994;Masucci et al, 1996), and denser cytoplasm (Dolan et al, 1994;Galway et al, 1994). In A. thaliana, most trichome patterning genes are also involved in root hair patterning (Schiefelbein, 2003;Schellmann et al, 2007).…”

“…The activity of this complex is counteracted by the partially redundant R3MYBs CAPRICE (CPC) and TRIPTYCHON (TRY; Wada et al, 1997;Schellmann et al, 2002;Schiefelbein, 2003) and their activator ENHANCER OF TRY AND CPC 1 (ETC1; Simon et al, 2007). Ultimately, the cooperation of these MYB, bHLH, and WD40 genes activates the expression of GLABRA2 (GL2), which encodes a homeodomain transcription factor that suppresses root hair development in non-root hair cells (Masucci et al, 1996).…”