title: CbCTB2, an O-methyltransferase is essential for biosynthesis of the phytotoxin cercosporin and infection of sugar beet by Cercospora beticola.
abstract: BACKGROUND
  Cercospora leaf spot disease, caused by the fungus Cercospora beticola, is the most destructive foliar disease of sugar beets (Beta vulgaris) worldwide. Cercosporin, a light-inducible toxin, is essential for necrosis of the leaf tissue and development of the typical leaf spots on sugar beet leaves.
  
  
  RESULTS
  In this study we show that the O-methyltransferase gene CTB2 is essential for cercosporin production and pathogenicity in two C. beticola isolates. We established a transformation system for C. beticola protoplasts, disrupted CTB2, and transformed the Δctb2 strains as well as a wild type strain with the DsRed reporter gene. The Δctb2 strains had lost their pigmentation and toxin measurements demonstrated that the Δctb2 strains were defective in cercosporin production. Infection of sugar beets with the wild type and Δctb2 DsRed strains showed that the deletion strain was severely impaired in plant infection. Histological analysis revealed that the CTB2-deficient isolate cannot enter the leaf tissue through stomata like the wild type.
  
  
  CONCLUSIONS
  Taken together, these observations indicate that cercosporin has a dual function in sugar beet infection: in addition to the well-known role in tissue necrosis, the toxin is required for the early phase of sugar beet infection.
authors.affiliation: Department of Molecular Phytopathology and Genetics, University of Hamburg, Biocenter Klein Flottbek, Ohnhorststr. 18, Hamburg 22609, Germany.
authors.forename: Cornelia
authors.initials: C
authors.lastname: Staerkel
authors.forename: Marike J
authors.initials: MJ
authors.lastname: Boenisch
authors.forename: Cathrin
authors.initials: C
authors.lastname: Kröger
authors.forename: Jörg
authors.initials: J
authors.lastname: Bormann
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Schäfer
authors.forename: Dietmar
authors.initials: D
authors.lastname: Stahl
mesh_terms: D001203:Ascomycota / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity*; D027461:Beta vulgaris / Q000382:microbiology*; D010569:Perylene / Q000031:analogs & derivatives* / Q000378:metabolism; D010935:Plant Diseases / Q000382:microbiology
chemical_list: D010569:Perylene; C026363:cercosporin