Institut für Pharmazeutische Biologie, Technische Universität Braunschweig, 38106 Braunschweig, Germany.
Plant Physiol. 2012 Feb;158(2):864-75. doi: 10.1104/pp.111.190918. Epub 2011 Dec 8.
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.
火疫病，由细菌 Erwinia amylovora 引起，是苹果（Malus × domestica）的一种毁灭性疾病。苹果的植物抗毒素是联苯和二苯并呋喃，其碳骨架由联苯合酶（BIS）形成，BIS 是一种 III 型聚酮合酶。在最近公布的苹果品种“金冠”基因组序列中，检测到 9 个 BIS 基因和 4 个 BIS 基因片段。这 9 个基因分为 4 个亚家族，分别称为 MdBIS1 到 MdBIS4。在系统发育树中，来自苹果和花楸的 BIS 氨基酸序列在功能多样的 III 型聚酮合酶的分支内形成了一个单独的聚类。从感染火疫病的苹果“Holsteiner Cox”枝条中克隆了 MdBIS1 到 MdBIS4 的 cDNA，在大肠杆菌中异源表达，并进行了功能分析。苯甲酰辅酶 A 和水杨酸辅酶 A 是首选的起始底物。在接种 E. amylovora 后，BIS3 基因在 cv Holsteiner Cox 的茎中表达，在坏死和健康组织之间的过渡区转录水平最高。过渡区是联苯和二苯并呋喃植物抗毒素的积累部位。叶片含有 BIS2 的转录本，但未能形成可检测到的 BIS 蛋白。在苹果“Cox Orange”的细胞培养物中，添加灭菌的 E. amylovora 悬浮液后，观察到 BIS1 到 BIS3 基因的表达。使用共聚焦激光扫描显微镜下的免疫荧光定位，在茎的过渡区检测到 BIS3 蛋白位于树皮的薄壁组织中。点状免疫荧光仅限于相邻皮层薄壁组织细胞之间的连接处。
