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The WUS homeobox-containing (WOX) protein family.

van der Graaff E, Laux T, Rensing SA - Genome Biol. (2009)

Bottom Line: The prototypic WOX-family member WUS has recently been shown to act as a bifunctional transcription factor, functioning as repressor in stem-cell regulation and as activator in floral patterning.Past research has mainly focused on part of the WOX protein family in some model flowering plants, such as Arabidopsis thaliana (thale cress) or Oryza sativa (rice).Future research, including so-far neglected clades and non-flowering plants, is expected to reveal how these master switches of plant differentiation and embryonic patterning evolved and how they fulfill their function.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Biology III, Faculty of Biology, University of Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany.

ABSTRACT
The WOX genes form a plant-specific subclade of the eukaryotic homeobox transcription factor superfamily, which is characterized by the presence of a conserved DNA-binding homeodomain. The analysis of WOX gene expression and function shows that WOX family members fulfill specialized functions in key developmental processes in plants, such as embryonic patterning, stem-cell maintenance and organ formation. These functions can be related to either promotion of cell division activity and/or prevention of premature cell differentiation. The phylogenetic tree of the plant WOX proteins can be divided into three clades, termed the WUS, intermediate and ancient clade. WOX proteins of the WUS clade appear to some extent able to functionally complement other members. The specific function of individual WOX-family proteins is most probably determined by their spatiotemporal expression pattern and probably also by their interaction with other proteins, which may repress their transcriptional activity. The prototypic WOX-family member WUS has recently been shown to act as a bifunctional transcription factor, functioning as repressor in stem-cell regulation and as activator in floral patterning. Past research has mainly focused on part of the WOX protein family in some model flowering plants, such as Arabidopsis thaliana (thale cress) or Oryza sativa (rice). Future research, including so-far neglected clades and non-flowering plants, is expected to reveal how these master switches of plant differentiation and embryonic patterning evolved and how they fulfill their function.

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Three-dimensional structure of homeodomains from different groups. (a) Crystal structure of the homeodomain from the mammalian ParaHox protein Pdx1 in complex with DNA [55] (PDB 2h1kB, visualized with NCBI MMDB [56] using Cn3D 4.1). (b) Visualization of the homeodomain shown in (a) without DNA, visualized with the Protein Picture Generator [57] using DINO [58]. (c) Visualization (carried out as in (b)) of the A. thaliana WUS homeodomain. Template search was conducted using HHSearch (identifying 2h1kB) and subsequent homology modeling using the alignment mode as implemented in SWISS-MODEL [59]. Note the two loop extensions (arrowed) in the WOX homeodomain as compared with the animal protein.
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Figure 2: Three-dimensional structure of homeodomains from different groups. (a) Crystal structure of the homeodomain from the mammalian ParaHox protein Pdx1 in complex with DNA [55] (PDB 2h1kB, visualized with NCBI MMDB [56] using Cn3D 4.1). (b) Visualization of the homeodomain shown in (a) without DNA, visualized with the Protein Picture Generator [57] using DINO [58]. (c) Visualization (carried out as in (b)) of the A. thaliana WUS homeodomain. Template search was conducted using HHSearch (identifying 2h1kB) and subsequent homology modeling using the alignment mode as implemented in SWISS-MODEL [59]. Note the two loop extensions (arrowed) in the WOX homeodomain as compared with the animal protein.

Mentions: The homeodomain binds DNA through a helix-turn-helix (HTH) structure. The HTH motif is characterized by two α-helices, which make intimate contacts with the DNA and are joined by a short turn. The second helix binds to DNA via a number of hydrogen bonds and hydrophobic interactions, which occur between specific side chains and the exposed bases and thymine methyl groups within the major groove of the DNA [9]. The recognized DNA core motifs differ. Homology modeling of the plant WOX homeodomain reveals two extended loops within a generally highly conserved structure as compared with the animal HOX homeodomain (Figure 2). Such extensions are also known from other HB families, for example the ancient TALE class homeodomain family [13], which has a three-amino-acid loop extension between helices 1 and 2 and has important roles in plant, animal and fungal development, for example as cofactors of the HOX proteins. The position of the homeodomain within the protein varies in different members of the WOX family (Figure 3).


The WUS homeobox-containing (WOX) protein family.

van der Graaff E, Laux T, Rensing SA - Genome Biol. (2009)

Three-dimensional structure of homeodomains from different groups. (a) Crystal structure of the homeodomain from the mammalian ParaHox protein Pdx1 in complex with DNA [55] (PDB 2h1kB, visualized with NCBI MMDB [56] using Cn3D 4.1). (b) Visualization of the homeodomain shown in (a) without DNA, visualized with the Protein Picture Generator [57] using DINO [58]. (c) Visualization (carried out as in (b)) of the A. thaliana WUS homeodomain. Template search was conducted using HHSearch (identifying 2h1kB) and subsequent homology modeling using the alignment mode as implemented in SWISS-MODEL [59]. Note the two loop extensions (arrowed) in the WOX homeodomain as compared with the animal protein.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2812940&req=5

Figure 2: Three-dimensional structure of homeodomains from different groups. (a) Crystal structure of the homeodomain from the mammalian ParaHox protein Pdx1 in complex with DNA [55] (PDB 2h1kB, visualized with NCBI MMDB [56] using Cn3D 4.1). (b) Visualization of the homeodomain shown in (a) without DNA, visualized with the Protein Picture Generator [57] using DINO [58]. (c) Visualization (carried out as in (b)) of the A. thaliana WUS homeodomain. Template search was conducted using HHSearch (identifying 2h1kB) and subsequent homology modeling using the alignment mode as implemented in SWISS-MODEL [59]. Note the two loop extensions (arrowed) in the WOX homeodomain as compared with the animal protein.
Mentions: The homeodomain binds DNA through a helix-turn-helix (HTH) structure. The HTH motif is characterized by two α-helices, which make intimate contacts with the DNA and are joined by a short turn. The second helix binds to DNA via a number of hydrogen bonds and hydrophobic interactions, which occur between specific side chains and the exposed bases and thymine methyl groups within the major groove of the DNA [9]. The recognized DNA core motifs differ. Homology modeling of the plant WOX homeodomain reveals two extended loops within a generally highly conserved structure as compared with the animal HOX homeodomain (Figure 2). Such extensions are also known from other HB families, for example the ancient TALE class homeodomain family [13], which has a three-amino-acid loop extension between helices 1 and 2 and has important roles in plant, animal and fungal development, for example as cofactors of the HOX proteins. The position of the homeodomain within the protein varies in different members of the WOX family (Figure 3).

Bottom Line: The prototypic WOX-family member WUS has recently been shown to act as a bifunctional transcription factor, functioning as repressor in stem-cell regulation and as activator in floral patterning.Past research has mainly focused on part of the WOX protein family in some model flowering plants, such as Arabidopsis thaliana (thale cress) or Oryza sativa (rice).Future research, including so-far neglected clades and non-flowering plants, is expected to reveal how these master switches of plant differentiation and embryonic patterning evolved and how they fulfill their function.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Biology III, Faculty of Biology, University of Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany.

ABSTRACT
The WOX genes form a plant-specific subclade of the eukaryotic homeobox transcription factor superfamily, which is characterized by the presence of a conserved DNA-binding homeodomain. The analysis of WOX gene expression and function shows that WOX family members fulfill specialized functions in key developmental processes in plants, such as embryonic patterning, stem-cell maintenance and organ formation. These functions can be related to either promotion of cell division activity and/or prevention of premature cell differentiation. The phylogenetic tree of the plant WOX proteins can be divided into three clades, termed the WUS, intermediate and ancient clade. WOX proteins of the WUS clade appear to some extent able to functionally complement other members. The specific function of individual WOX-family proteins is most probably determined by their spatiotemporal expression pattern and probably also by their interaction with other proteins, which may repress their transcriptional activity. The prototypic WOX-family member WUS has recently been shown to act as a bifunctional transcription factor, functioning as repressor in stem-cell regulation and as activator in floral patterning. Past research has mainly focused on part of the WOX protein family in some model flowering plants, such as Arabidopsis thaliana (thale cress) or Oryza sativa (rice). Future research, including so-far neglected clades and non-flowering plants, is expected to reveal how these master switches of plant differentiation and embryonic patterning evolved and how they fulfill their function.

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