Department of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana 61801, USA.
Phytopathology. 2010 Feb;100(2):192-8. doi: 10.1094/PHYTO-100-2-0192.
ABSTRACT Erwinia amylovora, the causal agent of fire blight, is considered to be a genetically homogeneous species based on physiological, biochemical, phylogenetic, and genetic analysis. However, E. amylovora strains exhibiting differential virulence are isolated from nature. The exopolysaccharide amylovoran and type III secretion system (T3SS) are two major yet separate virulence factors in E. amylovora. The objective of this study was to investigate whether there is a correlation between E. amylovora virulence and levels of virulence gene expression. Four wild-type strains (Ea1189, Ea273, Ea110, and CFBP1430), widely used in studies of E. amylovora pathogenesis, have been analyzed and compared. E. amylovora strains Ea273 and Ea110 elicited higher severity of disease symptoms than those of Ea1189 and CFBP1430 on apple cv. Golden Delicious and G16 apple root stock plants but not on susceptible Gala plants. In addition, Ea273 and Ea110 elicited severe hypersensitive responses within shorter periods of time at lower inoculum concentrations than those of Ea1189 and CFBP1430 on tobacco plants. Further molecular analyses have revealed that amylovoran production and expression of both amylovoran (amsG) and T3SS (dspE and hrpL) genes were significantly higher in Ea273 and Ea110 than those in Ea1189 and CFBP1430. Other phenotypes such as swarming motility in these four strains also differed significantly. These results indicate that E. amylovora strains of different origin can be divided into subgroups based on molecular signatures of virulence gene expression. Therefore, these molecular signatures may be used to differentiate E. amylovora strains, which may have taxonomical and evolutionary implications.
摘要 根据生理、生化、系统发育和遗传分析，火疫病病原体韧皮部欧文氏菌被认为是一个遗传上同质的物种。然而，自然界中分离到的韧皮部欧文氏菌菌株表现出不同的毒力。果聚糖（amylovoran）和 III 型分泌系统（T3SS）是韧皮部欧文氏菌的两个主要但独立的毒力因子。本研究旨在探讨韧皮部欧文氏菌的毒力与其毒力基因表达水平之间是否存在相关性。广泛用于研究韧皮部欧文氏菌发病机制的四个野生型菌株（Ea1189、Ea273、Ea110 和 CFBP1430）进行了分析和比较。在苹果品种 Golden Delicious 和 G16 砧木植株上，菌株 Ea273 和 Ea110 引起的病症严重程度高于 Ea1189 和 CFBP1430，而在易感 Gala 品种上则没有。此外，在烟草植株上，与 Ea1189 和 CFBP1430 相比，Ea273 和 Ea110 以更低的接种浓度在更短的时间内引起严重的过敏性坏死反应。进一步的分子分析表明，Ea273 和 Ea110 中果聚糖的产生和 amsG 以及 T3SS（dspE 和 hrpL）基因的表达水平均显著高于 Ea1189 和 CFBP1430。这四个菌株的其他表型，如游动能力，也有显著差异。这些结果表明，不同来源的韧皮部欧文氏菌菌株可以根据毒力基因表达的分子特征分为亚群。因此，这些分子特征可用于区分韧皮部欧文氏菌菌株，这可能具有分类学和进化意义。
