The Arabidopsis Athb‐10 (GLABRA2) is an HD‐Zip protein required for regulation of root hair development

Abstract

Homeodomain-leucine zipper (HD-Zip) proteins are putative transcription factors identified only in plants. Related Arabidopsis homeobox genes, isolated by virtue of sequence conservation within the helix-3 region of the homeodomain, fall into four families based on sequence similarity. This paper reports the characterization of Athb-10, a 747 amino acid protein belonging to the fourth HD-ZIP family. The studies indicate that, although less conserved, the leucine zipper of Athb-10 can functionally replace that of Athb-2 in an in vitro DNA-binding assay. Gene mapping experiments and sequence comparison analysis revealed that Athb-10 corresponds to GLABRA2, a homeodomain protein involved in trichome development. The mRNA expression analysis revealed that Athb-10/GLABRA2 is expressed not only in trichome-bearing organs, but also in the root. The analysis of wild-type and mutant plants showed that the Athb-10/GLABRA2 gene expression in the aerial part of the plant and in the root is affected by mutations at the TTG locus. Morphological analysis of the g/2-1 mutant revealed that the gene is necessary not only for local outgrowth of the trichome, but also for the regulation of root hair development in a subset of epidermal cells. Interestingly, the development of root hair cells in a position normally occupied by non-hair cells is dependent upon the ethylene regime in which the gl2-1 plants are grown. Sequence analysis of the gl2-1 allele revealed that the mutant gene encodes a truncated protein that might still retain a partial activity responsible for the formation of aborted trichomes and for the ethylene-dependent regulation of root hair formation.

Double Knockouts of Phospholipases Dζ1 and Dζ2 in Arabidopsis Affect Root Elongation during Phosphate-Limited Growth But Do Not Affect Root Hair Patterning

“…In Arabidopsis, the root epidermis is composed of two types of cell files, hair cell files and hairless cell files, of which only hair cell files produce root hairs (Dolan et al, 1993). Mutation of GLABRA2 (GL2) and TRANSPARENT TESTA GLABRA1 (TTG1) caused hairless cell files in the root epidermis to produce root hairs (Cristina et al, 1996). TTG1 was suggested to regulate GL2 positively, and GL2 regulates PLDz1 negatively by binding to its promoter region (Ohashi et al, 2003).…”

Arabidopsis TRANSPARENT TESTA GLABRA2Is Directly Regulated by R2R3 MYB Transcription Factors and Is Involved in Regulation ofGLABRA2Transcription in Epidermal Differentiation

“…Several genes involved in controlling root hair patterning have been identified. WERE-WOLF (WER) encodes an R2R3 MYB transcription factor, TRANSPARENT TESTA GLABRA1 (TTG1) encodes a WD40 protein, and GLABRA2 (GL2) encodes a homeodomain-leucine zipper (HD-ZIP) transcription factor, all of which are required to specify hairless cells (Galway et al, 1994;Rerie et al, 1994;Di Cristina et al, 1996;Masucci et al, 1996;Lee and Schiefelbein, 1999;Walker et al, 1999). When these genes are mutated, ectopic root hairs are formed from N cells.…”

Genome-Wide Characterization of the HD-ZIP IV Transcription Factor Family in Maize: Preferential Expression in the Epidermis

“…In Arabidopsis, the gl2 mutant shows abnormal trichome expansion and ectopic root hair differentiation (Rerie et al, 1994;Di Cristina et al, 1996), and the hdg11 mutant is characterized by excessive trichome branching (Nakamura et al, 2006). Consistent with the subepidermal layer expression of ANL2, the anl2 mutant does not produce subepidermal anthocyanin pigments and has an aberrant cellular organization of the primary root (Kubo et al, 1999).…”