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.