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Rop GTPase-dependent dynamics of tip-localized F-actin controls tip growth in pollen tubes.

Fu Y, Wu G, Yang Z - J. Cell Biol. (2001)

Bottom Line: Moreover, overexpression of RopGAP1 alone disrupted SABs and inhibited growth.Finally, SAB oscillates and appears at the tip before growth.Together, these results indicate that the dynamics of tip actin are essential for tip growth and provide the first direct evidence to link Rho GTPase to actin organization in controlling cell polarity and polar growth in plants.

View Article: PubMed Central - PubMed

Affiliation: Department of Botany and Plant Sciences, University of California, Riverside, California 92521, USA.

ABSTRACT
Tip-growing pollen tubes provide a useful model system to study polar growth. Although roles for tip-focused calcium gradient and tip-localized Rho-family GTPase in pollen tube growth is established, the existence and function of tip-localized F-actin have been controversial. Using the green fluorescent protein-tagged actin-binding domain of mouse talin, we found a dynamic form of tip-localized F-actin in tobacco pollen tubes, termed short actin bundles (SABs). The dynamics of SABs during polar growth in pollen tubes is regulated by Rop1At, a Rop GTPase belonging to the Rho family. When overexpressed, Rop1At transformed SAB into a network of fine filaments and induced a transverse actin band behind the tip, leading to depolarized growth. These changes were due to ectopic Rop1At localization to the apical region of the plasma membrane and were suppressed by guanine dissociation inhibitor overexpression, which removed ectopically localized Rop1At. Rop GTPase-activating protein (RopGAP1) overexpression, or Latrunculin B treatments, also recovered normal actin organization and tip growth in Rop1At-overexpressing tubes. Moreover, overexpression of RopGAP1 alone disrupted SABs and inhibited growth. Finally, SAB oscillates and appears at the tip before growth. Together, these results indicate that the dynamics of tip actin are essential for tip growth and provide the first direct evidence to link Rho GTPase to actin organization in controlling cell polarity and polar growth in plants.

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Effects of Latrunculin B on morphological phenotypes of pollen tubes overexpressing Rop1At or DN-rop1At. Pollen was transformed with different constructs and visualized using epifluorescence microscopy and a cooled CCD camera as described in Materials and Methods. A–C show typical morphology of untreated pollen tubes expressing GFP-mTalin alone (A), GFP-mTalin and Rop1At (B), and GFP-mTalin and DN-rop1 tube (C). D–F show typical morphology of pollen tubes treated with 5 nM Latrunculin B. Treated tubes expressing GFP-mTalin alone (D), GFP-mTalin and Rop1At (E), and GFP-mTalin and DN-rop1 tube (F). Bar, 50 μm.
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Figure 6: Effects of Latrunculin B on morphological phenotypes of pollen tubes overexpressing Rop1At or DN-rop1At. Pollen was transformed with different constructs and visualized using epifluorescence microscopy and a cooled CCD camera as described in Materials and Methods. A–C show typical morphology of untreated pollen tubes expressing GFP-mTalin alone (A), GFP-mTalin and Rop1At (B), and GFP-mTalin and DN-rop1 tube (C). D–F show typical morphology of pollen tubes treated with 5 nM Latrunculin B. Treated tubes expressing GFP-mTalin alone (D), GFP-mTalin and Rop1At (E), and GFP-mTalin and DN-rop1 tube (F). Bar, 50 μm.

Mentions: We then determined whether the rescue of actin organization in Rop1At-overexpressing cells by Latrunculin B leads to the recovery of normal tip growth. 3 h after Latrunculin B treatment, the length and the maximal width of pollen tubes were measured. As shown in Table and Fig. 6, Latrunculin B treatments suppressed tube expansion or tip swelling induced by either Rop1At or DN-rop1At overexpression. Latrunculin B treatment reduced the width of Rop1At-overexpressing pollen tubes from 19 to 12 μm. Similarly, this treatment also reduced the width of DN-rop1At tubes from 14 to 12 μm. These results suggest that Rop controls the polarity of pollen tube growth via dynamic tip-localized F-actin.


Rop GTPase-dependent dynamics of tip-localized F-actin controls tip growth in pollen tubes.

Fu Y, Wu G, Yang Z - J. Cell Biol. (2001)

Effects of Latrunculin B on morphological phenotypes of pollen tubes overexpressing Rop1At or DN-rop1At. Pollen was transformed with different constructs and visualized using epifluorescence microscopy and a cooled CCD camera as described in Materials and Methods. A–C show typical morphology of untreated pollen tubes expressing GFP-mTalin alone (A), GFP-mTalin and Rop1At (B), and GFP-mTalin and DN-rop1 tube (C). D–F show typical morphology of pollen tubes treated with 5 nM Latrunculin B. Treated tubes expressing GFP-mTalin alone (D), GFP-mTalin and Rop1At (E), and GFP-mTalin and DN-rop1 tube (F). Bar, 50 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2198818&req=5

Figure 6: Effects of Latrunculin B on morphological phenotypes of pollen tubes overexpressing Rop1At or DN-rop1At. Pollen was transformed with different constructs and visualized using epifluorescence microscopy and a cooled CCD camera as described in Materials and Methods. A–C show typical morphology of untreated pollen tubes expressing GFP-mTalin alone (A), GFP-mTalin and Rop1At (B), and GFP-mTalin and DN-rop1 tube (C). D–F show typical morphology of pollen tubes treated with 5 nM Latrunculin B. Treated tubes expressing GFP-mTalin alone (D), GFP-mTalin and Rop1At (E), and GFP-mTalin and DN-rop1 tube (F). Bar, 50 μm.
Mentions: We then determined whether the rescue of actin organization in Rop1At-overexpressing cells by Latrunculin B leads to the recovery of normal tip growth. 3 h after Latrunculin B treatment, the length and the maximal width of pollen tubes were measured. As shown in Table and Fig. 6, Latrunculin B treatments suppressed tube expansion or tip swelling induced by either Rop1At or DN-rop1At overexpression. Latrunculin B treatment reduced the width of Rop1At-overexpressing pollen tubes from 19 to 12 μm. Similarly, this treatment also reduced the width of DN-rop1At tubes from 14 to 12 μm. These results suggest that Rop controls the polarity of pollen tube growth via dynamic tip-localized F-actin.

Bottom Line: Moreover, overexpression of RopGAP1 alone disrupted SABs and inhibited growth.Finally, SAB oscillates and appears at the tip before growth.Together, these results indicate that the dynamics of tip actin are essential for tip growth and provide the first direct evidence to link Rho GTPase to actin organization in controlling cell polarity and polar growth in plants.

View Article: PubMed Central - PubMed

Affiliation: Department of Botany and Plant Sciences, University of California, Riverside, California 92521, USA.

ABSTRACT
Tip-growing pollen tubes provide a useful model system to study polar growth. Although roles for tip-focused calcium gradient and tip-localized Rho-family GTPase in pollen tube growth is established, the existence and function of tip-localized F-actin have been controversial. Using the green fluorescent protein-tagged actin-binding domain of mouse talin, we found a dynamic form of tip-localized F-actin in tobacco pollen tubes, termed short actin bundles (SABs). The dynamics of SABs during polar growth in pollen tubes is regulated by Rop1At, a Rop GTPase belonging to the Rho family. When overexpressed, Rop1At transformed SAB into a network of fine filaments and induced a transverse actin band behind the tip, leading to depolarized growth. These changes were due to ectopic Rop1At localization to the apical region of the plasma membrane and were suppressed by guanine dissociation inhibitor overexpression, which removed ectopically localized Rop1At. Rop GTPase-activating protein (RopGAP1) overexpression, or Latrunculin B treatments, also recovered normal actin organization and tip growth in Rop1At-overexpressing tubes. Moreover, overexpression of RopGAP1 alone disrupted SABs and inhibited growth. Finally, SAB oscillates and appears at the tip before growth. Together, these results indicate that the dynamics of tip actin are essential for tip growth and provide the first direct evidence to link Rho GTPase to actin organization in controlling cell polarity and polar growth in plants.

Show MeSH
Related in: MedlinePlus