Mo Y Y, Gross D C
Department of Plant Pathology, Washington State University, Pullman 99164-6430.
J Bacteriol. 1991 Sep;173(18):5784-92. doi: 10.1128/jb.173.18.5784-5792.1991.
The syrB gene is required for syringomycin production by Pseudomonas syringae pv. syringae and full virulence during plant pathogenesis. Strain B3AR132 containing a syrB::lacZ fusion was used to detect transcriptional activation of the syrB gene in syringomycin minimal medium by plant metabolites with signal activity. Among 34 plant phenolic compounds tested, arbutin, phenyl-beta-D-glucopyranoside, and salicin were shown to be strong inducers of syrB, giving rise to approximately 1,200 U of beta-galactosidase activity at 100 microM; esculin and helicin were moderate inducers, with about 250 to 400 U of beta-galactosidase activity at 100 microM. Acetosyringone and flavonoids that serve as signal molecules in Agrobacterium and Rhizobium species, respectively, did not induce the syrB::lacZ fusion. All syrB inducers were phenolic glucosides and none of the aglucone derivatives were active, suggesting that the beta-glycosidic linkage was necessary for signal activity. Phenyl-beta-D-galactopyranoside containing galactose substituted for glucose in the beta-glycosidic linkage also lacked inducer activity. Phenolic signal activity was enhanced two- to fivefold by specific sugars common to plant tissues, including D-fructose, D-mannose, and sucrose. The effect of sugars on syrB induction was most noticeable at low concentrations of phenolic glucoside (i.e., 1 to 10 microM), indicating that sugars such as D-fructose increase the sensitivity of P. syringae pv. syringae to the phenolic plant signal. Besides induction of syrB, syringomycin biosynthesis by parental strain B3A-R was induced to yield over 250 U of toxin by the additions of arbutin and D-fructose to syringomycin minimal medium. These data indicate that syringomycin production by most strains of P. syringae pv. syringae is modulated by the perception of two classes of plant signal molecules and transduced to the transcriptional apparatus of syringomycin (syr) genes such as syrB.
丁香假单胞菌丁香致病变种产生丁香霉素以及在植物致病过程中实现完全致病力均需要syrB基因。含有syrB::lacZ融合基因的菌株B3AR132被用于检测具有信号活性的植物代谢产物在丁香霉素基本培养基中对syrB基因的转录激活作用。在所测试的34种植物酚类化合物中，熊果苷、苯基-β-D-吡喃葡萄糖苷和水杨苷被证明是syrB的强诱导剂，在100微摩尔浓度时可产生约1200单位的β-半乳糖苷酶活性；七叶苷和秦皮苷是中度诱导剂，在100微摩尔浓度时具有约250至400单位的β-半乳糖苷酶活性。分别在农杆菌属和根瘤菌属中作为信号分子的乙酰丁香酮和类黄酮并未诱导syrB::lacZ融合基因。所有syrB诱导剂均为酚糖苷，其苷元衍生物均无活性，这表明β-糖苷键对于信号活性是必需的。在β-糖苷键中含有半乳糖取代葡萄糖的苯基-β-D-吡喃半乳糖苷也缺乏诱导活性。植物组织中常见的特定糖类（包括D-果糖、D-甘露糖和蔗糖）可使酚类信号活性增强2至5倍。糖类对syrB诱导的影响在低浓度酚糖苷（即1至微摩尔）时最为明显，这表明D-果糖等糖类会增加丁香假单胞菌丁香致病变种对植物酚类信号的敏感性。除了诱导syrB外，在丁香霉素基本培养基中添加熊果苷和D-果糖可诱导亲本菌株B3A-R产生丁香霉素，产量超过250单位毒素。这些数据表明，大多数丁香假单胞菌丁香致病变种产生丁香霉素是由两类植物信号分子的感知所调控，并传导至丁香霉素（syr）基因（如syrB）的转录装置。
