ACTIN2 is essential for bulge site selection and tip growth during root hair development of Arabidopsis. Plant Physiol

Institute of Plant Biology, University of Zurich, 8008 Zurich, Switzerland.
Plant physiology (Impact Factor: 6.84). 09/2002; 129(4):1464-72. DOI: 10.1104/pp.005777
Source: PubMed


Root hairs develop as long extensions from root epidermal cells. After the formation of an initial bulge at the distal end of the epidermal cell, the root hair structure elongates by tip growth. Because root hairs are not surrounded by other cells, root hair formation provides an excellent system for studying the highly complex process of plant cell growth. Pharmacological experiments with actin filament-interfering drugs have provided evidence that the actin cytoskeleton is an important factor in the establishment of cell polarity and in the maintenance of the tip growth machinery at the apex of the growing root hair. However, there has been no genetic evidence to directly support this assumption. We have isolated an Arabidopsis mutant, deformed root hairs 1 (der1), that is impaired in root hair development. The DER1 locus was cloned by map-based cloning and encodes ACTIN2 (ACT2), a major actin of the vegetative tissue. The three der1 alleles develop the mutant phenotype to different degrees and are all missense mutations, thus providing the means to study the effect of partially functional ACT2. The detailed characterization of the der1 phenotypes revealed that ACT2 is not only involved in root hair tip growth, but is also required for correct selection of the bulge site on the epidermal cell. Thus, the der1 mutants are useful tools to better understand the function of the actin cytoskeleton in the process of root hair formation.

Download full-text


Available from: Beat Keller, Jun 19, 2014
28 Reads
  • Source
    • "However, genetic analysis indicates that the two subclasses of vegetative actins have different function in multicellular development. Lack of the most abundant ACT2 gives rise to stunted and bulbous root hairs, but normal branching of leaf trichomes (Gilliland et al., 2002; Ringli et al., 2002; Kandasamy et al., 2009). In contrast, the other strongly expressed actin, ACT7, was suggested to affect seed germination, root growth and trichome branching, but not root hair development (Kandasamy et al., 2001, 2009; Gilliland et al., 2003). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Polar auxin transport and the action of the actin cytoskeleton are tightly interconnected, which is documented by the finding that auxin transporters reach their final destination by active movement of secretory vesicles along F-actin tracks. Moreover, auxin transporter polarity and flexibility is thought to depend on transporter cycling that requires endocytosis and exocytosis of vesicles.In this context, we have reviewed the current literature on an involvement of the actin cytoskeleton in polar auxin transport and identify known similarities and differences in its structure, function and dynamics in comparison to non-plant organisms. By describing how auxin modulates actin expression and actin organization and how actin and its stability affects auxin-transporter endocytosis and recycling, we discuss the current knowledge on regulatory auxin-actin feedback loops. We focus on known effects of auxin and of auxin transport inhibitors on the stability and organization of actin and examine the functionality of auxin and/or auxin transport inhibitor-binding proteins with respect to their suitability to integrate auxin/auxin transport inhibitor action.Finally, we indicate current difficulties in the interpretation of organ, time and concentration-dependent auxin/auxin transport inhibitor treatments and formulate simple future experimental guidelines. © The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email:
    Journal of Experimental Botany 06/2015; 66(16). DOI:10.1093/jxb/erv308 · 5.53 Impact Factor
  • Source
    • "To further examine whether the reduction in PIN2 intensity , polarization, and endocytosis and the increase in actin-filament bundling are necessary for the response to low Pi in Arabidopsis seedlings, we examined the response to low Pi of mutants of ACTIN2 (ACT2) (der1; Ringli et al., 2002), PIN2 (eir1; e.g. Luschnig et al., 1998; Abas et al., 2006), and the PIN-trafficking-associated protein TRANSPORT INHIBITOR RESISTANT3 (tir3; Desgagné-Penix et al., 2005). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Strigolactones (SLs) are plant hormones that regulate the plant response to phosphate (Pi) growth conditions. At least part of SL-signalling execution in roots involves MAX2-dependent effects on PIN2 polar localization in the plasma membrane (PM) and actin bundling and dynamics. We examined PIN2 expression, PIN2 PM localization, endosome trafficking, and actin bundling under low-Pi conditions: a MAX2-dependent reduction in PIN2 trafficking and polarization in the PM, reduced endosome trafficking, and increased actin-filament bundling were detected in root cells. The intracellular protein trafficking that is related to PIN proteins but unassociated with AUX1 PM localization was selectively inhibited. Exogenous supplementation of the synthetic SL GR24 to a SL-deficient mutant (max4) led to depletion of PIN2 from the PM under low-Pi conditions. Accordingly, roots of mutants in MAX2, MAX4, PIN2, TIR3, and ACTIN2 showed a reduced low-Pi response compared with the wild type, which could be restored by auxin (for all mutants) or GR24 (for all mutants except max2-1). Changes in PIN2 polarity, actin bundling, and vesicle trafficking may be involved in the response to low Pi in roots, dependent on SL/MAX2 signalling. © The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology.
    Journal of Experimental Botany 01/2015; 66(5). DOI:10.1093/jxb/eru513 · 5.53 Impact Factor
  • Source
    • "Consistently with the frequency of vesicular trafficking during root hair initiation and growth, GFP-RabA1d accumulation was lower at bulge stage than in growing root hairs. After the local structural changes that are required to define the bulge position, such as cytoskeleton rearrangements [64], cell wall composition [65,66] and accumulation of structural sterols in the plasma membrane [18], an increased vesicle trafficking is required during root hair elongation to provide a new plasma membrane in the expanding zone. This zone is filled with secretory and endocytotic vesicles [2], highly dynamic early endosomes in the clear zone and larger endosomal compartments in the subapical region [67]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Background Small Rab GTPases are important regulators of vesicular trafficking in plants. AtRabA1d, a member of the RabA1 subfamily of small GTPases, was previously found in the vesicle-rich apical dome of growing root hairs suggesting a role during tip growth; however, its specific intracellular localization and role in plants has not been well described.ResultsThe transient expression of 35S::GFP:RabA1d construct in Allium porrum and Nicotiana benthamiana revealed vesicular structures, which were further corroborated in stable transformed Arabidopsis thaliana plants. GFP-RabA1d colocalized with the trans-Golgi network marker mCherry-VTI12 and with early FM4-64-labeled endosomal comparments. Late endosomes and endoplasmic reticulum labeled with FYVE-DsRed and ER-DsRed, respectively, were devoid of GFP-RabA1d. The accumulation of GFP-RabA1d in the core of brefeldin A (BFA)-induced-compartments and the quantitative upregulation of RabA1d protein levels after BFA treatment confirmed the association of RabA1d with early endosomes/TGN and its role in vesicle trafficking. Light-sheet microscopy revealed involvement of RabA1d in root development. In root cells, GFP-RabA1d followed cell plate expansion consistently with cytokinesis-related vesicular trafficking and membrane recycling. GFP-RabA1d accumulated in disc-like structures of nascent cell plates, which progressively evolved to marginal ring-like structures of the growing cell plates. During root hair growth and development, GFP-RabA1d was enriched at root hair bulges and at the apical dome of vigorously elongating root hairs. Importantly, GFP-RabA1d signal intensity exhibited an oscillatory behavior in-phase with tip growth. Progressively, this tip localization dissapeared in mature root hairs suggesting a link between tip localization of RabA1d and root hair elongation. Our results support a RabA1d role in events that require vigorous membrane trafficking.Conclusions RabA1d is located in early endosomes/TGN and is involved in vesicle trafficking. RabA1d participates in both cell plate formation and root hair oscillatory tip growth. The specific GFP-RabA1d subcellular localization confirms a correlation between its specific spatio-temporal accumulation and local vesicle trafficking requirements during cell plate and root hair formation.
    BMC Plant Biology 09/2014; 14(1):252. DOI:10.1186/s12870-014-0252-0 · 3.81 Impact Factor
Show more