Received September 28, 2007
Accepted March 13, 2008
Cell wall modifications in Arabidopsis thaliana plants with altered 
-Larabinofuranosidase activity
Ricardo A. Chavez Montes , Philippe Ranocha , Yves Martinez , Zoran Minic , Lise Jouanin , Melanie Marquis , Luc Saulnier , Lynette M. Fulton , Christopher S. Cobbett , Frederique Bitton , Jean-Pierre Renou , Alain Jauneau , and Deborah Goffner *
UMR 5546 CNRS-UPS "Surfaces Cellulaires et Signalisation chez les Vegetaux", 24 chemin de Borde Rouge, BP 42617 Auzeville, 31326 Castanet-Tolosan, France; Laboratoire de Biologie Cellulaire, Institut National de la Recherche Agronomique, Route de St-Cyr, 78026 Versailles Cedex, France; Biopolymeres Interactions Assemblages, Unite de Recherche sur les Polysaccharides leurs Organisations et Interactions, Institut National de la Recherche Agronomique, BP 71627, 44316 Nantes Cedex 03, France; Department of Genetics, University of Melbourne, Victoria 3010, Australia; Unite de Recherche en Genomique Vegetale INRA-CNRS, 2 rue Gaston Cremieux, CP 5708, 91057 Evry cedex, France
* Corresponding author; email: goffner{at}scsv.ups-tlse.fr.
Although cell wall remodelling is an essential feature of plant growth and development, the underlying molecular mechanisms are poorly understood. This work describes the characterization of Arabidopsis thaliana plants with altered expression of ARAF1, a bifunctional 
-L-arabinofuranosidase / 
-D-xylosidase (At3g10740) belonging to family 51 glycosyl-hydrolases. ARAF1 was localized in several cell types in the vascular system of roots and stems including xylem vessels and parenchyma cells surrounding the vessels, the cambium, and the phloem. araf1 T-DNA insertional mutants showed no visible phenotype whereas transgenic plants that overexpressed ARAF1 exhibited a delay in inflorescence emergence and altered stem architecture. Although global monosaccharide analysis indicated only slight differences in cell wall composition in both mutant and overexpressing lines, immunolocalisation experiments using anti-arabinan (LM6) and anti-xylan (LM10) antibodies indicated cell type-specific alterations in cell wall structure. In araf1 mutants, an increase in LM6 signal intensity was observed in the phloem, cambium and xylem parenchyma in stems and roots, largely coinciding with ARAF1 expression sites. The ectopic overexpression of ARAF1 resulted in an increase in LM10 labelling in the secondary walls of interfascicular fibers and xylem vessels. The combined ARAF1 gene expression and immunolocalisation studies suggest that arabinan-containing pectins are potential in vivo substrates of ARAF1 in Arabidopsis.
