title: Differential expression of biphenyl synthase gene family members in fire-blight-infected apple 'Holsteiner Cox'.
abstract: Fire blight, caused by the bacterium Erwinia amylovora, is a devastating disease of apple (Malus × domestica). The phytoalexins of apple are biphenyls and dibenzofurans, whose carbon skeleton is formed by biphenyl synthase (BIS), a type III polyketide synthase. In the recently published genome sequence of apple 'Golden Delicious', nine BIS genes and four BIS gene fragments were detected. The nine genes fall into four subfamilies, referred to as MdBIS1 to MdBIS4. In a phylogenetic tree, the BIS amino acid sequences from apple and Sorbus aucuparia formed an individual cluster within the clade of the functionally diverse type III polyketide synthases. cDNAs encoding MdBIS1 to MdBIS4 were cloned from fire-blight-infected shoots of apple 'Holsteiner Cox,' heterologously expressed in Escherichia coli, and functionally analyzed. Benzoyl-coenzyme A and salicoyl-coenzyme A were the preferred starter substrates. In response to inoculation with E. amylovora, the BIS3 gene was expressed in stems of cv Holsteiner Cox, with highest transcript levels in the transition zone between necrotic and healthy tissues. The transition zone was the accumulation site of biphenyl and dibenzofuran phytoalexins. Leaves contained transcripts for BIS2 but failed to form immunodetectable amounts of BIS protein. In cell cultures of apple 'Cox Orange,' expression of the BIS1 to BIS3 genes was observed after the addition of an autoclaved E. amylovora suspension. Using immunofluorescence localization under a confocal laser-scanning microscope, the BIS3 protein in the transition zone of stems was detected in the parenchyma of the bark. Dot-shaped immunofluorescence was confined to the junctions between neighboring cortical parenchyma cells.
authors.affiliation: Institut für Pharmazeutische Biologie, Technische Universität Braunschweig, 38106 Braunschweig, Germany.
authors.forename: Cornelia
authors.initials: C
authors.lastname: Chizzali
authors.forename: Mariam M
authors.initials: MM
authors.lastname: Gaid
authors.forename: Asma K
authors.initials: AK
authors.lastname: Belkheir
authors.forename: Robert
authors.initials: R
authors.lastname: Hänsch
authors.forename: Klaus
authors.initials: K
authors.lastname: Richter
authors.forename: Henryk
authors.initials: H
authors.lastname: Flachowsky
authors.forename: Andreas
authors.initials: A
authors.lastname: Peil
authors.forename: Magda-Viola
authors.initials: MV
authors.lastname: Hanke
authors.forename: Benye
authors.initials: B
authors.lastname: Liu
authors.forename: Ludger
authors.initials: L
authors.lastname: Beerhues
mesh_terms: D003001:Cloning, Molecular; D018076:DNA, Complementary; D004926:Escherichia coli / Q000235:genetics; D017343:Genes, Plant; D007150:Immunohistochemistry; D027845:Malus / Q000201:enzymology / Q000235:genetics*; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics*; D010802:Phylogeny; D011994:Recombinant Proteins / Q000235:genetics
chemical_list: D018076:DNA, Complementary; D009097:Multienzyme Complexes; D011994:Recombinant Proteins