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A Sec14p-nodulin domain phosphatidylinositol transfer protein polarizes membrane growth of Arabidopsis thaliana root hairs.

Vincent P, Chua M, Nogue F, Fairbrother A, Mekeel H, Xu Y, Allen N, Bibikova TN, Gilroy S, Bankaitis VA - J. Cell Biol. (2005)

Bottom Line: Derangement of tip-directed Ca2+ gradients is also apparent and results from isotropic influx of Ca2+ from the extracellular milieu.We propose AtSfh1p regulates intracellular and plasma membrane phosphoinositide polarity landmarks that focus membrane trafficking, Ca2+ signaling, and cytoskeleton functions to the growing root hair apex.We further suggest that Sec14p-nodulin domain proteins represent a family of regulators of polarized membrane growth in plants.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Developmental Biology, Michael Hooker Microscopy Facility, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA. patrick_vincent@med.unc.edu

ABSTRACT
Phosphatidylinositol (PtdIns) transfer proteins (PITPs) regulate signaling interfaces between lipid metabolism and membrane trafficking. Herein, we demonstrate that AtSfh1p, a member of a large and uncharacterized Arabidopsis thaliana Sec14p-nodulin domain family, is a PITP that regulates a specific stage in root hair development. AtSfh1p localizes along the root hair plasma membrane and is enriched in discrete plasma membrane domains and in the root hair tip cytoplasm. This localization pattern recapitulates that visualized for PtdIns(4,5)P2 in developing root hairs. Gene ablation experiments show AtSfh1p izygosity compromises polarized root hair expansion in a manner that coincides with loss of tip-directed PtdIns(4,5)P2, dispersal of secretory vesicles from the tip cytoplasm, loss of the tip f-actin network, and manifest disorganization of the root hair microtubule cytoskeleton. Derangement of tip-directed Ca2+ gradients is also apparent and results from isotropic influx of Ca2+ from the extracellular milieu. We propose AtSfh1p regulates intracellular and plasma membrane phosphoinositide polarity landmarks that focus membrane trafficking, Ca2+ signaling, and cytoskeleton functions to the growing root hair apex. We further suggest that Sec14p-nodulin domain proteins represent a family of regulators of polarized membrane growth in plants.

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Defective organization of the MT cytoskeleton in AtSfh1p-deficient root hairs. (A) MT imaging in wild-type root hairs using MAP4-GFP. The cortical MT network is obvious. MTs in mutant single (B) and double (C) root hairs. Atsfh1::T-DNA root hairs fail to construct a defined cortical MT network. Bars, 20 μm.
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fig8: Defective organization of the MT cytoskeleton in AtSfh1p-deficient root hairs. (A) MT imaging in wild-type root hairs using MAP4-GFP. The cortical MT network is obvious. MTs in mutant single (B) and double (C) root hairs. Atsfh1::T-DNA root hairs fail to construct a defined cortical MT network. Bars, 20 μm.

Mentions: In addition to the f-actin cytoskeleton, MT networks also function in maintaining polarized tip growth (Bibikova et al., 1999; Baluška et al., 2000; Stevenson et al., 2000; Smith, 2003). MTs appear to consolidate the results of polarized membrane deposition, and MT action in supporting tip growth is spatially regulated by Ca2+ gradients (Bibikova et al., 1999; Baluška et al., 2000; Smith, 2003). To assess whether or not the derangements in Ca2+ signaling observed in Atsfh1::T-DNA root hairs coincided with functional derangement of MT systems, we probed root hair MT organization in AtSfh1p-deficient root hairs by GFP-MAP4 imaging (Marc et al., 1998). As reported by Smith (2003), cortical MTs were organized into discrete filaments. These MT filaments were arranged in spiraling profiles parallel to the longitudinal axis of the cortical plasma membrane in wild-type root hairs (Fig. 8 A and Video 8, available at http://www.jcb.org/cgi/content/full/jcb.200412074/DC1). In contrast, Atsfh1 root hairs exhibited only diffuse GFP-MAP4 staining profiles (Fig. 8, B and C; and Videos 9 and 10, available at http://www.jcb.org/cgi/content/full/jcb.200412074/DC1). Neither discrete filaments nor obvious spiraling profiles were seen. However, the body of the trichoblast from which the mutant root hair emanates did exhibit organized MTs (Fig. 8 C and Video 10). Thus, Atsfh izygous root hairs elaborate defects in MT assembly and/or organization that are limited to the growing root hair itself.


A Sec14p-nodulin domain phosphatidylinositol transfer protein polarizes membrane growth of Arabidopsis thaliana root hairs.

Vincent P, Chua M, Nogue F, Fairbrother A, Mekeel H, Xu Y, Allen N, Bibikova TN, Gilroy S, Bankaitis VA - J. Cell Biol. (2005)

Defective organization of the MT cytoskeleton in AtSfh1p-deficient root hairs. (A) MT imaging in wild-type root hairs using MAP4-GFP. The cortical MT network is obvious. MTs in mutant single (B) and double (C) root hairs. Atsfh1::T-DNA root hairs fail to construct a defined cortical MT network. Bars, 20 μm.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171805&req=5

fig8: Defective organization of the MT cytoskeleton in AtSfh1p-deficient root hairs. (A) MT imaging in wild-type root hairs using MAP4-GFP. The cortical MT network is obvious. MTs in mutant single (B) and double (C) root hairs. Atsfh1::T-DNA root hairs fail to construct a defined cortical MT network. Bars, 20 μm.
Mentions: In addition to the f-actin cytoskeleton, MT networks also function in maintaining polarized tip growth (Bibikova et al., 1999; Baluška et al., 2000; Stevenson et al., 2000; Smith, 2003). MTs appear to consolidate the results of polarized membrane deposition, and MT action in supporting tip growth is spatially regulated by Ca2+ gradients (Bibikova et al., 1999; Baluška et al., 2000; Smith, 2003). To assess whether or not the derangements in Ca2+ signaling observed in Atsfh1::T-DNA root hairs coincided with functional derangement of MT systems, we probed root hair MT organization in AtSfh1p-deficient root hairs by GFP-MAP4 imaging (Marc et al., 1998). As reported by Smith (2003), cortical MTs were organized into discrete filaments. These MT filaments were arranged in spiraling profiles parallel to the longitudinal axis of the cortical plasma membrane in wild-type root hairs (Fig. 8 A and Video 8, available at http://www.jcb.org/cgi/content/full/jcb.200412074/DC1). In contrast, Atsfh1 root hairs exhibited only diffuse GFP-MAP4 staining profiles (Fig. 8, B and C; and Videos 9 and 10, available at http://www.jcb.org/cgi/content/full/jcb.200412074/DC1). Neither discrete filaments nor obvious spiraling profiles were seen. However, the body of the trichoblast from which the mutant root hair emanates did exhibit organized MTs (Fig. 8 C and Video 10). Thus, Atsfh izygous root hairs elaborate defects in MT assembly and/or organization that are limited to the growing root hair itself.

Bottom Line: Derangement of tip-directed Ca2+ gradients is also apparent and results from isotropic influx of Ca2+ from the extracellular milieu.We propose AtSfh1p regulates intracellular and plasma membrane phosphoinositide polarity landmarks that focus membrane trafficking, Ca2+ signaling, and cytoskeleton functions to the growing root hair apex.We further suggest that Sec14p-nodulin domain proteins represent a family of regulators of polarized membrane growth in plants.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Developmental Biology, Michael Hooker Microscopy Facility, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA. patrick_vincent@med.unc.edu

ABSTRACT
Phosphatidylinositol (PtdIns) transfer proteins (PITPs) regulate signaling interfaces between lipid metabolism and membrane trafficking. Herein, we demonstrate that AtSfh1p, a member of a large and uncharacterized Arabidopsis thaliana Sec14p-nodulin domain family, is a PITP that regulates a specific stage in root hair development. AtSfh1p localizes along the root hair plasma membrane and is enriched in discrete plasma membrane domains and in the root hair tip cytoplasm. This localization pattern recapitulates that visualized for PtdIns(4,5)P2 in developing root hairs. Gene ablation experiments show AtSfh1p izygosity compromises polarized root hair expansion in a manner that coincides with loss of tip-directed PtdIns(4,5)P2, dispersal of secretory vesicles from the tip cytoplasm, loss of the tip f-actin network, and manifest disorganization of the root hair microtubule cytoskeleton. Derangement of tip-directed Ca2+ gradients is also apparent and results from isotropic influx of Ca2+ from the extracellular milieu. We propose AtSfh1p regulates intracellular and plasma membrane phosphoinositide polarity landmarks that focus membrane trafficking, Ca2+ signaling, and cytoskeleton functions to the growing root hair apex. We further suggest that Sec14p-nodulin domain proteins represent a family of regulators of polarized membrane growth in plants.

Show MeSH
Related in: MedlinePlus