scholarly journals ROP Gtpase–Dependent Dynamics of Tip-Localized F-Actin Controls Tip Growth in Pollen Tubes

2001 ◽  
Vol 152 (5) ◽  
pp. 1019-1032 ◽  
Author(s):  
Ying Fu ◽  
Guang Wu ◽  
Zhenbiao Yang
Keyword(s):  
Tip Growth ◽  
Fluorescent Protein ◽  
Rho Gtpase ◽  
Pollen Tubes ◽  
Actin Binding ◽  
Apical Region ◽  
Polar Growth ◽  
Actin Organization ◽  
Rop Gtpase ◽  
Rho Family

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.

scholarly journals Oscillatory ROP GTPase Activation Leads the Oscillatory Polarized Growth of Pollen Tubes

2005 ◽  
Vol 16 (11) ◽  
pp. 5385-5399 ◽  
Author(s):  
Jae-Ung Hwang ◽  
Ying Gu ◽  
Yong-Jik Lee ◽  
Zhenbiao Yang
Keyword(s):  
Gene Expression ◽  
Molecular Mechanisms ◽  
Tip Growth ◽  
Rho Gtpase ◽  
Cell Movement ◽  
Pollen Tubes ◽  
Common Mechanism ◽  
Rop Gtpase ◽  
Growth Oscillation ◽  
Gtpase Activation

Oscillation regulates a wide variety of processes ranging from chemotaxis in Dictyostelium through segmentation in vertebrate development to circadian rhythms. Most studies on the molecular mechanisms underlying oscillation have focused on processes requiring a rhythmic change in gene expression, which usually exhibit a periodicity of >10 min. Mechanisms that control oscillation with shorter periods (<10 min), presumably independent of gene expression changes, are poorly understood. Oscillatory pollen tube tip growth provides an excellent model to investigate such mechanisms. It is well established that ROP1, a Rho-like GTPase from plants, plays an essential role in polarized tip growth in pollen tubes. In this article, we demonstrate that tip-localized ROP1 GTPase activity oscillates in the same frequency with growth oscillation, and leads growth both spatially and temporally. Tip growth requires the coordinate action of two ROP1 downstream pathways that promote the accumulation of tip-localized Ca2+and actin microfilaments (F-actin), respectively. We show that the ROP1 activity oscillates in a similar phase with the apical F-actin but apparently ahead of tip-localized Ca2+. Furthermore, our observations support the hypothesis that the oscillation of tip-localized ROP activity and ROP-dependent tip growth in pollen tubes is modulated by the two temporally coordinated downstream pathways, an early F-actin assembly pathway and a delayed Ca2+gradient-forming pathway. To our knowledge, our report is the first to demonstrate the oscillation of Rho GTPase signaling, which may be a common mechanism underlying the oscillation of actin-dependent processes such as polar growth, cell movement, and chemotaxis.

scholarly journals Localization of a Rho GTPase Implies a Role in Tip Growth and Movement of the Generative Cell in Pollen Tubes.

1996 ◽  
pp. 293-303 ◽  
Author(s):  
Y. Lin ◽  
Y. Wang ◽  
J. K. Zhu ◽  
Z. Yang
Keyword(s):  
Tip Growth ◽  
Rho Gtpase ◽  
Generative Cell ◽  
Pollen Tubes

scholarly journals The Giardia lamellipodium-like ventrolateral flange supports attachment and rapid cytokinesis

2021 ◽  
Author(s):  
William R. Hardin ◽  
Germain C. M. Alas ◽  
Nikita Taparia ◽  
Elizabeth B. Thomas ◽  
Melissa Steele-Ogus ◽  
...  
Keyword(s):  
Rho Gtpase ◽  
Actin Binding ◽  
Binding Domains ◽  
Truncation Mutant ◽  
Membrane Protrusions ◽  
Ventral Disc ◽  
Rho Family ◽  
Attachment Mechanism ◽  
Host Parasite ◽  
Membrane Reservoir

AbstractAttachment to the intestinal epithelium is critical to the lifestyle of the ubiquitous parasite Giardia lamblia. The microtubule cytoskeleton plays a well characterized role in attachment via the ventral adhesive disc, whereas the role of the unconventional actin cytoskeleton is controversial. We identified a novel actin associated protein with putative WH2-like actin binding domains we named Flangin. Flangin complexes with Giardia actin and is enriched in the ventrolateral flange (VLF), a lamellipodium-like membrane protrusion at the interface between parasites and attached surfaces. Live imaging revealed that the VLF grows to ~1 μm in width after cytokinesis, then remains size-uniform in interphase, grows during mitosis, and is resorbed during cytokinesis. A Flangin truncation mutant stabilizes the VLF and blocks cytokinesis, indicating that the VLF is a membrane reservoir supporting rapid myosin-independent cytokinesis in Giardia. Rho family GTPases are important regulators of membrane protrusions, GlRac, the sole Rho family GTPase in Giardia, was localized to the VLF. Knockdown of Flangin, actin, and GlRac result in VLF formation defects indicating a conserved role for GlRac and actin in forming membrane protrusions, despite the absence of canonical actin binding proteins that link Rho GTPase signaling to lamellipodia formation. Flangin-depleted parasites challenged with fluid shear force in flow chambers had a reduced ability to remain attached, indicating a role for the VLF in attachment. This secondary attachment mechanism complements the microtubule based adhesive ventral disc, a feature that is particularly important during mitosis when the parental ventral disc begins disassembly in preparation for cytokinesis.ImportanceThe ventrolateral flange (VLF) is a lamellipodium-like structure found at the host-parasite interface that has long been thought to be involved in parasite attachment. The proteins responsible for building the VLF have remained unidentified precluding manipulation of the VLF to determine its role in Giardia biology. We identified Flangin, a novel actin associated protein that localizes to the VLF, implicating Giardia actin in VLF formation. We demonstrate that: 1.) Flangin, actin, and GlRac are required for VLF formation, 2.) the VLF serves as a membrane reservoir to support Giardia’s incredibly fast cytokinesis, and 3) the VLF augments attachment, which is critical to parasitism. The microtubule-based adhesive ventral disc and the actin-based ventrolateral flange represent redundant means of maintaining attachment, the presence of redundant systems illustrate the importance of attachment to the lifestyle of this ubiquitous parasite.

scholarly journals Rho GTPase ROP1 Interactome Analysis Reveals Novel ROP1-Associated Pathways for Pollen Tube Polar Growth in Arabidopsis

2020 ◽  
Vol 21 (19) ◽  
pp. 7033
Author(s):  
Hui Li ◽  
Jinbo Hu ◽  
Jing Pang ◽  
Liangtao Zhao ◽  
Bing Yang ◽  
...  
Keyword(s):  
Cell Growth ◽  
Pollen Tube ◽  
Rho Gtpase ◽  
Ion Homeostasis ◽  
Pollen Tubes ◽  
Polar Growth ◽  
Cell Wall Modification ◽  
Polar Cell ◽  
Associated Proteins ◽  
Arabidopsis Pollen

ROP (Rho-like GTPases from plants) GTPases are polarly localized key regulators of polar growth in pollen tubes and other cells in plants. However, how ROP GTPases are regulated and how they control polar growth remains to be fully understood. To gain new insights into ROP-dependent mechanisms underlying polar cell growth, we characterized the interactome of ROP1 GTPase that controls Arabidopsis pollen tube (PT) tip growth, an extreme form of polar cell growth. We established an efficient method for culturing Arabidopsis pollen tubes in liquid medium, which was used for immunoprecipitation/mass spectrometry-based identification of ROP1-associated proteins. A total of 654 candidates were isolated from the ROP1 interactome in Arabidopsis pollen tubes, and GO (Gene Ontology) classification and pathway analysis revealed multiple uncharacterized ROP1-dependent processes including translation, cell wall modification, post transcriptional modification, and ion homeostasis, in addition to known ROP1-dependent pathways. The ROP1-interactome data was further supported by the co-expression of the candidate interactors in highly mature pollen with PT germination and growth defects being discovered in 25% (8/32) of the candidate mutant genes. Taken together, our work uncovers valuable information for the identification and functional elucidation of ROP-associated proteins in the regulation of polar growth, and provides a reliable reference to identify critical regulators of polar cell growth in the future.

Localization of a Rho GTPase Implies a Role in Tip Growth and Movement of the Generative Cell in Pollen Tubes

1996 ◽  
Vol 8 (2) ◽  
pp. 293 ◽  
Author(s):  
Yakang Lin ◽  
Yalai Wang ◽  
Jian-kang Zhu ◽  
Zhenbiao Yang
Keyword(s):  
Tip Growth ◽  
Rho Gtpase ◽  
Generative Cell ◽  
Pollen Tubes

scholarly journals Wsp1 Is Downstream of Cin1 and Regulates Vesicle Transport and Actin Cytoskeleton as an Effector of Cdc42 and Rac1 in Cryptococcus neoformans

2012 ◽  
Vol 11 (4) ◽  
pp. 471-481 ◽  
Author(s):  
Gui Shen ◽  
Erxun Zhou ◽  
J. Andrew Alspaugh ◽  
Ping Wang
Keyword(s):  
Actin Cytoskeleton ◽  
Cryptococcus Neoformans ◽  
Actin Polymerization ◽  
Fluorescent Protein ◽  
Rho Gtpase ◽  
Pathogenic Fungus ◽  
Vacuolar Membrane ◽  
Vesicle Transport ◽  
Content Type ◽  
Actin Organization

ABSTRACTHuman Wiskott-Aldrich syndrome protein (WASP) is a scaffold linking upstream signals to the actin cytoskeleton. In response to intersectin ITSN1 and Rho GTPase Cdc42, WASP activates the Arp2/3 complex to promote actin polymerization. The human pathogenCryptococcus neoformanscontains the ITSN1 homolog Cin1 and the WASP homolog Wsp1, which share more homology with human proteins than those of other fungi. Here we demonstrate that Cin1, Cdc42/Rac1, and Wsp1 function in an effector pathway similar to that of mammalian models. In thecin1mutant, expression of the autoactivated Wsp1-B-GBD allele partially suppressed the mutant defect in endocytosis, and expression of the constitutively activeCDC42Q61Lallele restored normal actin cytoskeleton structures. Similar phenotypic suppression can be obtained by the expression of a Cdc42-green fluorescent protein (GFP)-Wsp1 fusion protein. In addition, Rac1, which was found to exhibit a role in early endocytosis, activates Wsp1 to regulate vacuole fusion. Rac1 interacted with Wsp1 and depended on Wsp1 for its vacuolar membrane localization. Expression of the Wsp1-B-GBD allele restored vacuolar membrane fusion in therac1mutant. Collectively, our studies suggest novel ways in which this pathogenic fungus has adapted conserved signaling pathways to control vesicle transport and actin organization, likely benefiting survival within infected hosts.

scholarly journals Exocytosis and endocytosis: coordinating and fine-tuning the polar tip growth domain in pollen tubes

2020 ◽  
Vol 71 (8) ◽  
pp. 2428-2438 ◽  
Author(s):  
Jingzhe Guo ◽  
Zhenbiao Yang
Keyword(s):  
Cell Wall ◽  
Rho Gtpases ◽  
Intracellular Signaling ◽  
Tip Growth ◽  
Apical Cell ◽  
Turgor Pressure ◽  
Pollen Tubes ◽  
Fine Tuning ◽  
Rop Gtpase ◽  
Specialized Form

Abstract Pollen tubes rapidly elongate, penetrate, and navigate through multiple female tissues to reach ovules for sperm delivery by utilizing a specialized form of polar growth known as tip growth. This process requires a battery of cellular activities differentially occurring at the apical growing region of the plasma membrane (PM), such as the differential cellular signaling involving calcium (Ca2+), phospholipids, and ROP-type Rho GTPases, fluctuation of ions and pH, exocytosis and endocytosis, and cell wall construction and remodeling. There is an emerging understanding of how at least some of these activities are coordinated and/or interconnected. The apical active ROP modulates exocytosis to the cell apex for PM and cell wall expansion differentially occurring at the tip. The differentiation of the cell wall involves at least the preferential distribution of deformable pectin polymers to the apex and non-deformable pectin polymers to the shank of pollen tubes, facilitating the apical cell expansion driven by high internal turgor pressure. Recent studies have generated inroads into how the ROP GTPase-based intracellular signaling is coordinated spatiotemporally with the external wall mechanics to maintain the tubular cell shape and how the apical cell wall mechanics are regulated to allow rapid tip growth while maintaining the cell wall integrity under the turgor pressure. Evidence suggests that exocytosis and endocytosis play crucial but distinct roles in this spatiotemporal coordination. In this review, we summarize recent advances in the regulation and coordination of the differential pectin distribution and the apical domain of active ROP by exocytosis and endocytosis in pollen tubes.

scholarly journals A Rho family GTPase controls actin dynamics and tip growth via two counteracting downstream pathways in pollen tubes

2005 ◽  
Vol 169 (1) ◽  
pp. 127-138 ◽  
Author(s):  
Ying Gu ◽  
Ying Fu ◽  
Peter Dowd ◽  
Shundai Li ◽  
Vanessa Vernoud ◽  
...  
Keyword(s):  
Pollen Tube ◽  
Tip Growth ◽  
Rho Gtpase ◽  
Plant Cells ◽  
Actin Dynamics ◽  
Actin Assembly ◽  
Filamentous Actin ◽  
Growth Defects ◽  
Spatiotemporal Regulation ◽  
Rho Family

Tip growth in neuronal cells, plant cells, and fungal hyphae is known to require tip-localized Rho GTPase, calcium, and filamentous actin (F-actin), but how they interact with each other is unclear. The pollen tube is an exciting model to study spatiotemporal regulation of tip growth and F-actin dynamics. An Arabidopsis thaliana Rho family GTPase, ROP1, controls pollen tube growth by regulating apical F-actin dynamics. This paper shows that ROP1 activates two counteracting pathways involving the direct targets of tip-localized ROP1: RIC3 and RIC4. RIC4 promotes F-actin assembly, whereas RIC3 activates Ca2+ signaling that leads to F-actin disassembly. Overproduction or depletion of either RIC4 or RIC3 causes tip growth defects that are rescued by overproduction or depletion of RIC3 or RIC4, respectively. Thus, ROP1 controls actin dynamics and tip growth through a check and balance between the two pathways. The dual and antagonistic roles of this GTPase may provide a unifying mechanism by which Rho modulates various processes dependent on actin dynamics in eukaryotic cells.

scholarly journals Nifedipine-sensitive calcium channels are involved in polar growth of lily pollen tubes

1985 ◽  
Vol 76 (1) ◽  
pp. 247-254
Author(s):  
H.D. Reiss ◽  
W. Herth
Keyword(s):  
Calcium Channels ◽  
Tip Growth ◽  
Lilium Longiflorum ◽  
Pollen Tubes ◽  
Polar Growth ◽  
Treatment Results ◽  
High Tendency ◽  
Lily Pollen ◽  
Internal Calcium

Pollen germination and tube growth of Lilium longiflorum in vitro are affected by 10(−5) M-nifedipine. Germinating ‘tubes’ form broad protuberances along the whole colpus. Short tubes show a high tendency to grow ‘amoeboid-like’ and to branch; or a second tube emerges in another region of the colpus. Longer tubes (greater than or equal to 100 micron) broaden irregularly or swell at their tips. The diameter of the tube can vary drastically within the same tube. With increasing time of treatment many tubes burst. Normal tip growth stops within 10 min, but protoplasmic streaming continues even after 15 h. More or less regularly, wall thickenings are formed along the whole tube or on the flanks of the germinating region after some hours. The internal calcium gradient, visualized by chlorotetracycline (CTC) fluorescence, is also disturbed. Nifedipine treatment results in uniform or irregular CTC fluorescence. Branching tubes temporarily show a new subapical CTC gradient. After 6–8 h of nifedipine treatment many cells are no longer stainable with CTC. The results indicate the presence of nifedipine-sensitive calcium channels in pollen tubes.

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