title: Trans-Golgi network localized small GTPase RabA1d is involved in cell plate formation and oscillatory root hair growth.
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.
  
  
  RESULTS
  The 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 compartments. 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.
authors.forename: Tobias
authors.initials: T
authors.lastname: Berson
authors.forename: Daniel
authors.initials: D
authors.lastname: von Wangenheim
authors.forename: Tomáš
authors.initials: T
authors.lastname: Takáč
authors.forename: Olga
authors.initials: O
authors.lastname: Šamajová
authors.forename: Amparo
authors.initials: A
authors.lastname: Rosero
authors.forename: Miroslav
authors.initials: M
authors.lastname: Ovečka
authors.forename: George
authors.initials: G
authors.lastname: Komis
authors.forename: Ernst H K
authors.initials: EH
authors.lastname: Stelzer
authors.forename: Jozef
authors.initials: J
authors.lastname: Šamaj
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D048749:Cytokinesis; D017930:Genes, Reporter; D019697:Onions / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D021381:Protein Transport; D040901:Proteomics; D011993:Recombinant Fusion Proteins; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D021601:trans-Golgi Network / Q000201:enzymology
chemical_list: D029681:Arabidopsis Proteins; D011993:Recombinant Fusion Proteins; C000602386:RabA1d protein, Arabidopsis; D020691:rab GTP-Binding Proteins