title: Callose biosynthesis in Arabidopsis with a focus on pathogen response: what we have learned within the last decade.
abstract: BACKGROUND
  (1,3)-β-Glucan callose is a cell wall polymer that is involved in several fundamental biological processes, ranging from plant development to the response to abiotic and biotic stresses. Despite its importance in maintaining plant integrity and plant defence, knowledge about the regulation of callose biosynthesis at its diverse sites of action within the plant is still limited. The moderately sized family of GSL (GLUCAN SYNTHASE-LIKE) genes is predicted to encode callose synthases with a specific biological function and subcellular localization. Phosphorylation and directed translocation of callose synthases seem to be key post-translational mechanisms of enzymatic regulation, whereas transcriptional control of GSL genes might only have a minor function in response to biotic or abiotic stresses.
  
  
  CONCLUSIONS
  Among the different sites of callose biosynthesis within the plant, particular attention has been focused on the formation of callose in response to pathogen attack. Here, callose is deposited between the plasma membrane and the cell wall to act as a physical barrier to stop or slow invading pathogens. Arabidopsis (Arabidopsis thaliana) is one of the best-studied models not only for general plant defence responses but also for the regulation of pathogen-induced callose biosynthesis. Callose synthase GSL5 (GLUCAN SYNTHASE-LIKE5) has been shown to be responsible for stress-induced callose deposition. Within the last decade of research into stress-induced callose, growing evidence has been found that the timing of callose deposition in the multilayered system of plant defence responses could be the key parameter for optimal effectiveness. This timing seems to be achieved through co-ordinated transport and formation of the callose synthase complex.
authors.affiliation: Phytopathology and Biochemistry, Biocenter Klein Flottbek, University of Hamburg, Ohnhorststrasse 18, 22609 Hamburg, Germany.
authors.forename: Dorothea
authors.initials: D
authors.lastname: Ellinger
authors.affiliation: Phytopathology and Biochemistry, Biocenter Klein Flottbek, University of Hamburg, Ohnhorststrasse 18, 22609 Hamburg, Germany christian.voigt@uni-hamburg.de.
authors.forename: Christian A
authors.initials: CA
authors.lastname: Voigt
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D005936:Glucans / Q000378:metabolism*; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism*; D054884:Host-Pathogen Interactions; D047071:beta-Glucans / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D005936:Glucans; D047071:beta-Glucans; C048306:callose; D005964:Glucosyltransferases; C040232:glucan synthase; C020570:1,3-beta-glucan synthase
keywords: (1,3)-β-glucan; Arabidopsis thaliana; callose biosynthesis; callose synthase; innate immunity; microbial pathogens; papillae; pathogen response; plant cell wall polymer; plant defence; vesicle transport