Cui Y, Madi L, Mukherjee A, Dumenyo C K, Chatterjee A K
Department of Plant Pathology, University of Missouri, Columbia 65211, USA.
Mol Plant Microbe Interact. 1996 Sep;9(7):565-73. doi: 10.1094/mpmi-9-0565.
Erwinia carotovora subsp. carotovora wild-type strain Ecc71 does not elicit the hypersensitive reaction (HR) in tobacco leaves. By mini-Tn5-Km and chemical mutagenesis we have isolated RsmA- mutants of Ecc71 that produce high basal levels of pectate lyases, polygalacturonase, cellulase, and protease; they also are hypervirulent. The RsmA- mutants, but not their parent strains, elicit an HR-like response in tobacco leaves. This reaction is characterized by the rapid appearance of water soaking followed by tissue collapse and necrosis. The affected areas remain limited to the region infiltrated with bacterial cells, and the symptoms closely resemble a typical HR, e.g., the reactions caused by Pseudomonas syringae pv. pisi. Moreover, low concentrations of cells of the mini-Tn5-Km insertion RsmA- mutant, AC5070, infiltrated into tobacco leaf tissue prevent elicitation of the rapid necrosis by AC5070 or by P. syringae pv. pisi. Elicitation of the HR-like response by the mutants is not affected by the deficiency of N-(3-oxohexanoyl)-L-homoserine lactone, the cell density (quorum) sensing signal. Cloning and sequence analysis have disclosed that E. carotovora subsp. carotovora strain Ecc71 possesses a homolog of E. chrysanthemi hrpN known to encode an elicitor of the HR; the corresponding Ecc71 gene is designated hrpNEcc. Northern (RNA) blot data show that the level of hrpNEcc mRNA is considerably higher in the RsmA- mutants than in the RsmA+ strains. Moreover, a low copy plasmid carrying the rsmA+ allele severely reduces the level of the hrpNEcc transcripts in the RsmA- mutants. These constructs, like the RsmA+ E. carotovora subsp. carotovora strains, do not elicit the HR-like response. These data taken along with the effects of rsmA on exoenzyme production and pathogenicity (A. Chatterjee et al., 1995, Appl. Environ. Microbiol. 61:1959-1967) demonstrate that this global regulator gene plays a critical role in plant interaction of E. carotovora subsp. carotovora.
胡萝卜软腐欧文氏菌胡萝卜软腐亚种野生型菌株Ecc71不会在烟草叶片中引发过敏反应（HR）。通过mini-Tn5-Km和化学诱变，我们分离出了Ecc71的RsmA突变体，这些突变体产生高水平的果胶酸裂解酶、多聚半乳糖醛酸酶、纤维素酶和蛋白酶；它们也具有更强的致病性。RsmA突变体而非其亲本菌株，会在烟草叶片中引发类似HR的反应。这种反应的特征是迅速出现水渍状，随后组织塌陷和坏死。受影响的区域仅限于细菌细胞浸润的区域，症状与典型的HR非常相似，例如由丁香假单胞菌豌豆致病变种引起的反应。此外，将低浓度的mini-Tn5-Km插入RsmA突变体AC5070的细胞浸润到烟草叶组织中，可防止AC5070或丁香假单胞菌豌豆致病变种引发快速坏死。突变体引发的类似HR的反应不受N-（3-氧代己酰基）-L-高丝氨酸内酯（群体感应信号）缺乏的影响。克隆和序列分析表明，胡萝卜软腐欧文氏菌胡萝卜软腐亚种菌株Ecc71拥有菊苣欧文氏菌hrpN的同源物，已知该同源物编码HR的激发子；相应的Ecc71基因被命名为hrpNEcc。Northern（RNA）印迹数据表明，hrpNEcc mRNA的水平在RsmA突变体中比在RsmA +菌株中高得多。此外，携带rsmA +等位基因的低拷贝质粒会严重降低RsmA突变体中hrpNEcc转录本的水平。这些构建体，与RsmA +胡萝卜软腐欧文氏菌胡萝卜软腐亚种菌株一样，不会引发类似HR的反应。这些数据以及rsmA对胞外酶产生和致病性的影响（A. Chatterjee等人，1995年，《应用与环境微生物学》61:1959 - 1967）表明，这个全局调节基因在胡萝卜软腐欧文氏菌胡萝卜软腐亚种与植物的相互作用中起关键作用。
