The homeobox gene GLABRA2 is required for position-dependent cell differentiation in the root epidermis of Arabidopsis thaliana

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.

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A role for the RabA4b effector protein PI-4Kβ1 in polarized expansion of root hair cells in Arabidopsis thaliana

The Journal of Cell Biology ◽

10.1083/jcb.200508116 ◽

2006 ◽

Vol 172 (7) ◽

pp. 991-998 ◽

Cited By ~ 188

Author(s):

Mary L. Preuss ◽

Aaron J. Schmitz ◽

Julie M. Thole ◽

Heather K.S. Bonner ◽

Marisa S. Otegui ◽

...

Keyword(s):

Arabidopsis Thaliana ◽

Hair Cells ◽

Root Hair ◽

Root Hairs ◽

Developmentally Regulated ◽

Domain Specific ◽

Polarized Secretion ◽

Phosphatidylinositol 4 ◽

Golgi Network ◽

Root Hair Cells

The RabA4b GTPase labels a novel, trans-Golgi network compartment displaying a developmentally regulated polar distribution in growing Arabidopsis thaliana root hair cells. GTP bound RabA4b selectively recruits the plant phosphatidylinositol 4-OH kinase, PI-4Kβ1, but not members of other PI-4K families. PI-4Kβ1 colocalizes with RabA4b on tip-localized membranes in growing root hairs, and mutant plants in which both the PI-4Kβ1 and -4Kβ2 genes are disrupted display aberrant root hair morphologies. PI-4Kβ1 interacts with RabA4b through a novel homology domain, specific to eukaryotic type IIIβ PI-4Ks, and PI-4Kβ1 also interacts with a Ca2+ sensor, AtCBL1, through its NH2 terminus. We propose that RabA4b recruitment of PI-4Kβ1 results in Ca2+-dependent generation of PI-4P on this compartment, providing a link between Ca2+ and PI-4,5P2–dependent signals during the polarized secretion of cell wall components in tip-growing root hair cells.

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Supra-physiological levels of Gibberellins/DELLAs alter the patterning, morphology and abundance of root hairs in root tips of A. thaliana seedlings

10.1101/2021.07.15.452505 ◽

2021 ◽

Author(s):

Iva McCarthy-Suarez

Keyword(s):

Gene Expression ◽

Cell Fate ◽

Epidermal Cell ◽

Root Hair ◽

Root Hairs ◽

Root Tip ◽

Spatial Patterning ◽

Root Tips ◽

Root Epidermis

In spite of the known role of gibberellins (GAs), and of their antagonistic proteins, the DELLAs, in leaf hair production, no investigations, however, have assessed their hypothetical function in the production of root hairs. To this aim, the effects of supra-physiological levels of GAs/DELLAs on the spatial patterning of gene expression of the root hair (CPC) and root non-hair (GL2, EGL3 and WER) epidermal cell fate markers, as well as on the distribution, morphology and abundance of root hairs, were studied in root tips of 5-day-old A. thaliana seedlings. Results showed that excessive levels of GAs/DELLAs impaired the spatial patterning of gene expression of the root hair/non-hair epidermal cell fate markers, as well as the arrangement, shape and frequency of root hairs, giving rise to ectopic hairs and ectopic non-hairs, two-haired cells, two-tipped hairs, branched hairs, longer and denser hairs near the root tip under excessive DELLAs, and shorter and scarcer hairs near the root tip under excessive GAs. However, when the gai-1 (GA-insensitive-1) DELLA mutant protein was specifically over-expressed at the root epidermis, no changes in the patterning or abundance of root hairs occurred. Thus, these results suggest that, in seedlings of A. thaliana, the GAs/DELLAs might have a role in regulating the patterning, morphology and abundance of root hairs by acting from the sub-epidermal tissues of the root.

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Clonal relationships and cell patterning in the root epidermis of Arabidopsis

Development ◽

10.1242/dev.120.9.2465 ◽

1994 ◽

Vol 120 (9) ◽

pp. 2465-2474 ◽

Cited By ~ 21

Author(s):

C. M. Duckett ◽

C. Grierson ◽

P. Linstead ◽

K. Schneider ◽

E. Lawson ◽

...

Keyword(s):

Hair Cells ◽

Root Hair ◽

Root Meristem ◽

Cell Types ◽

Root Cap ◽

Size Difference ◽

Cortical Cells ◽

Root Epidermis ◽

Tangential Wall ◽

Root Hair Cells

The development of the post-embryonic root epidermis of Arabidopsis thaliana is described. Clonal analysis has identified three sets of initials that give rise to the columella root cap cells, epidermis and lateral root-cap cells, and the cells of the cortex and endodermis respectively. The mature epidermis is composed of two cell types, root hair cells (derived from trichoblasts) and non- hair cells (derived from atrichoblasts). These cells are arranged in sixteen or more discrete files. Each hair cell file overlies the anticlinal (radial) wall of the underlying cortical cells and is separated from the next by one or two non-hair files. The root hair forms as a tip-growing projection from the basal end of the trichoblast i.e. the end nearest the root meristem. The non-hair epidermal cells are significantly longer than the hair forming cells and are located over the outer periclinal (tangential) wall of the underlying cortical cells. The size difference between the two cell types is apparent in the cell division zone before hairs form. This suggests that the signals required for the differentiation of the root epidermis function in the meristem itself. Ectopic hairs are present in the ctr1 root epidermis suggesting that a Raf protein kinase may play a role in pattern formation/differentiation in the root epidermis and that ethylene may be a diffusible signal involved in specifying pattern in the root epidermis.

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Asymmetric growth of root epidermal cells is related to the differentiation of root hair cells in Hordeum vulgare (L.)

Journal of Experimental Botany ◽

10.1093/jxb/ert300 ◽

2013 ◽

Vol 64 (16) ◽

pp. 5145-5155 ◽

Cited By ~ 26

Author(s):

Marek Marzec ◽

Michael Melzer ◽

Iwona Szarejko

Keyword(s):

Hordeum Vulgare ◽

Hair Cells ◽

Root Hair ◽

Epidermal Cells ◽

Hordeum Vulgare L ◽

Asymmetric Growth ◽

Root Hair Cells

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Root Hair Specific Proteins in Glycine max

Zeitschrift für Naturforschung C ◽

10.1515/znc-1987-0508 ◽

1987 ◽

Vol 42 (5) ◽

pp. 537-541 ◽

Cited By ~ 2

Author(s):

Dietrich Werner ◽

Andreas Bernd Wolff

Keyword(s):

Glycine Max ◽

Root System ◽

Hair Cells ◽

Root Hair ◽

Root Hairs ◽

Target Cells ◽

Molecular Weights ◽

Organ Specific ◽

Specific Proteins ◽

Root Hair Cells

Abstract In root hairs from seedlings of Glycine max cultivars, isolated from the root system and com pared with the complete organ, specific soluble proteins have been found. By FPLC chromatography and SDS gel electrophoresis root hair specific proteins with molecular weights of 13, 21, 34, 38 and 42 kDa were separated. Additionally, proteins with molecular weights of 12, 20, 69 and 74 kDa were significantly enriched in root hairs compared to roots without root hairs. By using CNBr activated Sepharose with antibodies against the root system without root hairs, the pres ence of root hair specific proteins was confirmed in extracts from isolated root hair cells. Enrichment of Fe and Ca in some of the proteins from the root hairs is demonstrated. The present knowledge of the biochemical specificity of legume root hairs, the target cells of Rhizobium and Bradyrhizobium infection, is discussed.

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A cell surface arabinogalactan-peptide influences root hair cell fate

10.1101/787143 ◽

2019 ◽

Cited By ~ 1

Author(s):

Cecilia Borassi ◽

Javier Gloazzo Dorosz ◽

Martiniano M. Ricardi ◽

Laercio Pol Fachin ◽

Mariana Carignani Sardoy ◽

...

Keyword(s):

Arabidopsis Thaliana ◽

Transcription Factor ◽

Cell Surface ◽

Cell Fate ◽

Root Hair ◽

Root Hairs ◽

Epidermal Cells ◽

Root Epidermis ◽

A Cell ◽

Epidermis Cell

SummaryRoot hairs (RHs) develop from specialized epidermal cells called trichoblasts, whereas epidermal cells that lack RHs are known as atrichoblasts. The mechanism controlling root epidermal cell fate is only partially understood. Root epidermis cell fate is regulated by a transcription factor complex that promotes the expression of the homeodomain protein GLABRA 2 (GL2), which blocks RH development by inhibiting ROOT HAIR DEFECTIVE 6 (RHD6). Suppression of GL2 expression activates RHD6, a series of downstream TFs including ROOT HAIR DEFECTIVE 6 LIKE-4 (RSL4 [Yi et al. 2010]) and their target genes, and causes epidermal cells to develop into RHs. Brassinosteroids (BRs) influence root epidermis cell fate. In the absence of BRs, phosphorylated BIN2 (a Type-II GSK3-like kinase) inhibits a protein complex that directly downregulates GL2 [Chen et al. 2014]. Here, we show that the genetic and pharmacological perturbation of the arabinogalactan peptide (AG) AGP21 in Arabidopsis thaliana, triggers aberrant RH development, similar to that observed in plants with defective BR signaling. We reveal that an O-glycosylated AGP21 peptide, which is positively regulated by BZR1, a transcription factor activated by BR signaling, affects RH cell fate by altering GL2 expression in a BIN2-dependent manner. These results suggest that perturbation of a cell surface AGP disrupts BR responses and inhibits the downstream effect of BIN2 on the RH repressor GL2 in root epidermal cells. In addition, AGP21 also acts in a BR-independent, AGP-dependent mode that together with BIN2 signalling cascade controls RH cell fate.SignificanceIn the plant Arabidopsis thaliana, the root epidermis forms in an alternating pattern atrichoblasts with trichoblast cells that end up developing root hairs (RHs). Atrichoblast cell fate is directly promoted by the transcription factor GLABRA2 (GL2) while the lack of GL2 allows RH formation. The loss of AGP21 peptide triggers an abnormal RH cell fate in two contiguous cells in a similar manner as brassinosteroid (BRs) mutants. In the absence of BR signaling, BIN2 (a GSK3 like-kinase) in a phosphorylated state, downregulate GL2 expression to trigger RH cell fate. The absence of AGP21 is able to repress GL2 expression and activates the expression of RSL4 and EXP7 root hair proteins.

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