title: The Brassicaceae species Heliophila coronopifolia produces root border-like cells that protect the root tip and secrete defensin peptides.
abstract: Root border cells and border-like cells (BLCs), the latter originally described in Arabidopsis thaliana , have been described as cells released at the root tips of the species in which they occur. BLCs are thought to provide protection to root meristems similar to classical root border cells. In addition, four defensin peptides (Hc-AFP1-4) have previously been characterized from Heliophila coronopifolia , a South African semi-desert flower, and found to be strongly antifungal. This provided an opportunity to evaluate if the BLCs of H. coronopifolia indeed produce these defensins, which would provide evidence towards a defence role for BLCs.
  
  
  
  Fluorescence microscopy, using live-cell-imaging technology, was used to characterize the BLCs of H. coronopifolia . Quantitative real-time PCR (qRT-PCR) analysis and immunofluorescence microscopy was used to characterize these defensin peptides.
  
  
  
  BLCs originated at the root apical meristem and formed a protective sheath at the tip and along the sides as the root elongated in solid medium. BLCs have a cellulose-enriched cell wall, intact nuclei and are embedded in a layer of pectin-rich mucilage. Pectinase treatments led to the dissolution of the sheath and dissociation of the root BLCs. Hc-AFP1-4 genes were all expressed in root tissues, but Hc-AFP3 transcripts were the most abundant in these tissues as measured by qRT-PCR. A polyclonal antibody that was cross-reactive with all four defensins, and probably recognizing a general plant defensin epitope, was used in fluorescence microscopy analysis to examine the presence of the peptides in the root tip and BLCs. Data confirmed the peptides present in the root tip tissues, the mucilage sheath and the BLCs.
  
  
  
  This study provides a link between defensin peptides and BLCs, both embedded in a protective pectin mucilage sheath, during normal plant growth and development. The presence of the Hc-AFP3 defensin peptides in the BLCs suggests a role for these cells in root protection.
authors.affiliation: Institute for Wine Biotechnology, Department of Viticulture and Oenology, Faculty of AgriSciences, Stellenbosch University, Matieland 7602, South Africa.|Laboratoire Glycobiologie et Matrice Extracellulaire Végétale (Glyco-MEV), Grand Réseau de Recherche VASI de Haute Normandie, Normandie Université, Université de Rouen, 76821 Mont Saint Aignan cedex, France.
authors.forename: Florent
authors.initials: F
authors.lastname: Weiller
authors.affiliation: Institute for Wine Biotechnology, Department of Viticulture and Oenology, Faculty of AgriSciences, Stellenbosch University, Matieland 7602, South Africa.
authors.forename: John P
authors.initials: JP
authors.lastname: Moore
authors.affiliation: Institute for Wine Biotechnology, Department of Viticulture and Oenology, Faculty of AgriSciences, Stellenbosch University, Matieland 7602, South Africa.
authors.forename: Philip
authors.initials: P
authors.lastname: Young
authors.affiliation: Laboratoire Glycobiologie et Matrice Extracellulaire Végétale (Glyco-MEV), Grand Réseau de Recherche VASI de Haute Normandie, Normandie Université, Université de Rouen, 76821 Mont Saint Aignan cedex, France.
authors.forename: Azeddine
authors.initials: A
authors.lastname: Driouich
authors.affiliation: Institute for Wine Biotechnology, Department of Viticulture and Oenology, Faculty of AgriSciences, Stellenbosch University, Matieland 7602, South Africa.
authors.forename: Melané A
authors.initials: MA
authors.lastname: Vivier
mesh_terms: D019607:Brassicaceae / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D023082:Defensins / Q000235:genetics / Q000378:metabolism*; D018519:Meristem / Q000166:cytology / Q000276:immunology; D008856:Microscopy, Fluorescence; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000166:cytology / Q000276:immunology; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D023082:Defensins; D010940:Plant Proteins
keywords: Brassicaceae; Hc-AFP; Heliophila coronopifolia; defensins; pectin-rich mucilage; pectinase; root border-like cells