瓜类细菌性果斑病菌组氨酸营养缺陷型与致病性相关

Relationshjip of histidine auxotrophy of Acidovorax citrulli with pathogenicity

摘要:

摘要: 瓜类细菌性果斑病菌(Acidovorax citrulli，Ac)是近年来发生在西瓜、甜瓜等葫芦科植物上的一种重要病原细菌。它主要危害西瓜、甜瓜，引起叶斑或叶枯，造成果实腐烂，严重时导致绝产。【目的】验证组氨酸的合成缺陷与Ac 的致病性之间的关系。【方法】采用Mini-Tn5 转座子随机插入方法，从瓜类细菌性果斑病菌xjl12 突变体文库中筛选突变体，并通过亚克隆技术对基因进行鉴定。【结果】筛选到一株在烟草上失去过敏反应且致病性降低的突变体。鉴定其为hisC(histidinol-phosphate aminotransferase) 基因的突变体。同时也对Ac 中组氨酸合成过程中的另外3 个酶(hisA、hisB 和hisD 基因) 进行了研究。这些基因突变后均丧失了激发烟草过敏性反应的能力，致病性明显下降，发病时间比野生型延迟了约48 h，通过外源添加组氨酸可恢复其突变特征。【结论】这些基因的突变所致性状改变与组氨酸的合成缺陷直接相关。

Abstract:

Abstract: Acidovorax citrulli(Ac) is an important bacterium that occurs in watermelon，melon and other cucurbits．It mainly damages watermelon and melon，and can cause leaf blight，fruit rot，and even mortality．［Objective］To verify the relationship between defects in the synthesis of histidine and the pathogenicity of Ac．［Methods］We generated a transposon (Tn5) mutant library on the background of strain xjl12 of Ac． Then we used subclone technology to identify the gene．［Results］The mutant could not elicit the hypersensitive response (HR) in nonhost tobacco，and its virulence was reduced． It is impaired in hisC，which encodes the protein histidinolphosphate aminotransferase． The other three genes (hisA，hisB and hisD) involved in the process of histidine synthesis were also studied． These mutants could not elicit the hypersensitive response (HR) in nonhost tobacco; their virulence was reduced significantly and disease symptoms caused by mutants were delayed for 48 hours when compared to the wild type strain． By adding exogenous histidine，pathogenicity of the mutants was restored.［Conclusion］The change of the characteristics of the mutants was directly related to the synthesis of histidine.